---

 

SARGON

 

A COMPUTER
CHESS PROGRAM

 

DAN AND KATHE SPRACKLEN

 

---

Block diagram

 

---

HAYDEM BOOK COMPANY, INC.
Rochelle Park, New Jersey
ISBN 0-8104-51554
Library of Congress Catalog Card Number 78-64981

Copyright © 1978 by HAVDEN BOOK COMPANY, INC. All rights reserved.
No part of this book may be reprinted, or reproduced, or utilized in any
form or by any electronic, mechanical, or other means, now known or
hereafter invented, including photocopying and recording, or in any infor-
mation storage and retrieval system, without permission in writing from
the Publisher.

Printed in the United States of America

       4  5  6  7  8  9    PRINTING
--------------------------------------------
79 80 81 82 83 84 85 86	   YEAR

 

---

 

CONTENTS

Meet Sargon	1
The Chessboard in Computer Graphics	3
Chess Piece Summary	6
Users Guide to Sargon	11
Notes on the Implementation of Sargon	17
Equates	19
Direction Tables	20
Point Value Array	20
Board Array	21
Attack List	22
Pinned Piece Array	22
Score and Ply Tables	23
Table Indices Section	24
Variables Section	25
Move List Section	27
Board Setup Routine	28
Path Routine	29
Piece Mover Routine	30
En Passant Routine	32
Adjust Move List Pointer	33
Castle Routine	34
Admove Routine	36
Generate Move Routine	37
Check Routine	38
Attack Routine	39
Attack Save Routine	42
Pin Check Routine	43
Pin Find Routine	44
Exchange Routine	47
Next Attacker/Defender Routine	48
Point Evaluation Routine	49
Limit Routine	51
Move Routine	54
Un-Move Routine	56
Sort Routine	58
Evaluation Routine	59
Find Move Routine	60
Ascend Tree Routine	64
One Move Book Opening	65
Graphics Data Base	66
Standard Message	67
Graphics Variables	68
I/0 Macro Definitions	68
Main Program Driver	69
Interrogation for Ply & Color	71
Computer Move Routine	73
Forced Mate Handling	75
Tab to Player's Column	76
Tab to Computer's Column	76
Tab to Player's Column w/o Move No	77
Tab to Computer's Column w/o Move No	77
Board Index to ASCII Square Name	78
Player's Move Analysis	79
ASCII Square Name to Board Index	80
Validate Move Subroutine	81
Accept Input Character	82
New Page if Needed	83
Display Mated King	84
Set Up Position for Analysis	85
Update Positions of Royalty	88
Set Up Empty Board	89
Insert Piece Subroutine	91
Board Index to Norm Address Subr	93
Positive Integer Division	94
Positive Integer Multiplication	94
Square Blinker	95
Execute Move Subroutine	97
Make Move Subroutine	98
TDL/ZILOG Mnemonics Conversion	99
Index to Subroutines	113

MEET SARGON

 

SARGON is a computer chess program by Dan and Kathe Spracklen. In March 1978 it took first place in the first chess tournament held strictly for microcomputers. The tournament took place during the 2-1/2 days of the 1978 West Coast Computer Faire and drew large crowds each day. When the last battle ended, SARGON had won 5 games of 5 played. A tie existed for second place, with 3 programs scoring a total of 3 points in the 5 rounds.

SARGON is written in Z-80 assembly language using the TDL Macro Assembler. The program occupies 8K of RAM, which includes 2K of data areas, 2K graphics display and user interface, and 4K move logic. The move logic is the heart of SARGON. It is displayed in the block diagram as the set of routines called by FNDMOV (Find Move). FNDMOV controls the search for the computer's best move by performing a depth first-tree search using the techniques of alpha beta pruning. Listed first under FNDMOV's calls on the block diagram is PINFND (Pin Find Routine). PINFND produces a list of all pieces pinned against the king or queen for both white and black. Pinned pieces must be treated carefully when analyzing battles engaged on the chess board, since their attacking power may be an illusion. FNDMOV also calls POINTS (Point Evaluation Routine). POINTS performs a static evaluation and derives a score for a given board position. POINTS takes factors of material, board control, and development into account. Predominant in the evaluation is material. Material scores must be adjusted to reflect unresolved battles on the chess board. It is the function of XCHNG (Exchange Evaluation Routine) to judge the outcome of these unresolved battles. The factors of development and board control are not allowed to dominate the move choice. LIMIT is called to truncate the contribution of those factors to the score.

FNDMOV controls the generation of legal moves by GENMOV (Generate Move Routine). GENMOV produces the move set for all of the pieces of a given color. For each piece in turn, GENMOV calls MPIECE (Piece Mover Routine), which generates all the possible legal moves for a given piece. MPIECE itself calls a series of routines. PATH generates a single possible move for a given piece along its current path of motion. ADMOVE adds a move to the move list. CASTLE and ENPSNT (En Passant Pawn Capture Routine) handle the special moves. After MPIECE has produced all legal moves, GENMOV calls INCHK, which determines whether or not the king is in check.

Basic to the success of alpha beta pruning is the sorting of moves generated at each ply level. FNDMOV calls SORTM (Sort Routine) to accomplish this task. A sort is dependent on an evaluation, so SORTM calls EVAL (Evaluation Routine). To evaluate a given move on the move list, E VAL first makes the move on the board by calling MOVE. It is determined if the move is legal by calling INCHK. Then, if the move is legal, it is evaluated by calling PNFND and POINTS. Finally, EVAL restores the board position by calling UNMOVE.

The bookkeeping required by alpha beta pruning is for the most part coded in line in FNDMOV. However, FNDMOV calls ASCEND (Ascend Tree Routine) to adjust all the parameters in transferring the parameters up one ply in the tree.

At the bottom of FNDMOV's call list on the block diagram is BOOK. BOOK provides, an opening book of a single move. lfwhite, SARGON will play P-K4 or P-Q4 at random. If black, SARGON replies to any opening move with P-K4 or P-Q4, whichever is most appropriate.

The move selection logic of FNDMOV is embedded in a whole network of routines that forms SARGON's interface to the outside world. The DRIVER routine initiates and coordinates, the entire game. First on the block diagram in DRIVER's list of calls is CHARTR (Accept Input Character). CHARTR is a totally machine-dependent input routine whose sole purpose is to accept a single character input from the keyboard. All machine-dependent aspects of SARGON have been isolated in this manner to simplify conversion to Z-80 machines running under different operating systems. Machine-dependent code appears in only two other places. The first is the macro definition area, where all the output functions are listed, and the second is in the routine DSPBRD (Display Graphics Board and Pieces), where machine-dependent lines of code are clearly marked.

Next on the block diagram is ANALYS (Set Up Position for Analysis). ANALYS allows the user to set the board to any position of his choosing. The routine blinks the graphics board squares in turn, allowing the user to input a piece ofhis choice or leave the contents unchanged. When the board has been set to the desired arrangement of pieces, play of the game may be resumed. ANALYS also provides a handy means of correcting a move entered by mistake.

As a part of game initialization, DRIVER calls INTERR (Interrogate for Ply and Color). INTERR questions the player for his choice of white or black, and allows him to select the depth of search. DSPBRD and INITBD complete initialization by setting up the graphics board display and internal board array. PGIFND (New Page if Needed) and TBCPCL (Tab to Computer's Column) are used to control spacing in the move list. The move list is displayed to the left of the graphics board on the video screen.

The most important routines called by DRIVER are, of course, CPTRMV and PLYRMV, which are control routines for the computer's and player's moves, respectively. Central to CPTRM V is FNDMOV, the logic to select the computer's move, which has already been discussed. Below FNDMOV on the block diagram is FCDMAT (Forced Mate Handling). If the computer is checkmated, it acknowledges the fact with a message displayed in the move list and by tipping over its king. Assuming the computer is not mated, MOVE makes the chosen move on the board array and EXECMV displays it on the graphics board. In displaying the move, the piece first blinks a few times, moves to its new location, and then blinks a few times again. The function of BITASN (Board Index to ASCII Square Name) is to convert the internal move into a representation in algebraic chess notation on the move list, then INCHK determines whether or not the computer should call "Check."

When the opponent is on the move, PLYRMV controls the events. It calls CHARTR to accept the move entry. ASNTBI (ASCII Square Name to Board Index) converts the move to internal representation. Then VALMOV checks the player's move for validity. If the move is legal, EXECMV displays it on the graphics board as in CPTRMV. PGIFND (New Page if Needed) aadTRPLCL (Tab to Player's Column) control spacing in the move list.

The Chess Board in Computer Graphics

A graphics display is an eye-catching addition to a chess program. For the human player, a visual display of the board is far easier to relate to than a scheme which creates an array using purely alphabetic characters. Graphics display requires specialized hardware, and degree of resolution varies with existing displays. The SARGON program features a complete graphite board display. The video screen of the Jupiter III microcomputer, on which it is implemented, has a 96 x 128 dot graphics matrix. The screen display is controlled by a 2k area of static RAM. Information may be displayed on the screen by storing the desired values in that 2k area. So only moue instructions are required for graphics display.

The SARGON display utilizes 96 x 96 dots for the graphics chess board. The remaining area is used to list the moves of the game in algebraic chess notation. The display is arranged as follows:
The empty board and move list area are displayed using the block move feature of the Z-80. It requires no stored data. The memory required to store the piece shapes has been kept to a minimum through use ofthe concept of boundary and kernel dots.

Graphics Characters

By varying and combining bits that are turned on, a total of 64 different graphics characters may be produced. For example:

Now, 1010 0101 = 165 in decimal, which can be used as the ASCII code for this character.

 

Pillar and Bar Formatlnq

We've seen how individual dots are grouped into blocks of six dots each. The blocks are then laid out like tiles to cover the display area. So a dot matrix that is 12 x 12 would look like:

User's Guide to SARGON

1. To begin execution:

   The start address of SARGON will vary depnding on the load address. It will always be the address of DRIVER. Once execution has begiun, SARGON will ask you a series of queations:

   "Welcome to Chess. Care for a Game?"

    

   To playa game of chess respond with "y." An answer of "n" will get you to the routine that allows you to set up a boats position. (See Item 5.)

   "Would you like to play white (w) or black (b)?"

   The player selects white by entering "w" or black by "b." Any other key defaults to black. White always moves first.

   "Select look ahead (1-6),"

   This allows the player to select the depth of search. For example, if you select 3 ply, SARGON will consider:

   1. All of his possible moves.
   2. All of your responses to those move,.
   3. All of his possible replies to your responses.
   At this point, the boats display will appear on the screen. If you choose white, SARGON will be waiting for your move entry. If you choose black, SARGON will make its move on the board, print it in the move list, and then ..it for your move entry.

    

2. To enter a move:

   Moves must be entered in algebraic these notation. This means you most tell SARGON the file and rank coordinates of the squares you are moving from and to. The files are lettered a-h and the ranks are numbered 1-8. So the coordinates of the board are:
   

   The move itself is entered as ff-tt so to play the king's pawn up two squares you would enter:

   "e2-e4"

   If SARGON responded with the same move, it would print:

   "e7-e5"

    

   Just enter the king's move. The rook will tag along. for example, if you are white and you wish to castle king's side, enter:

   "e1-g1"

   You will see both your king and rook move. When SARGON castles, he lists it as 0-0 or 0-0-0 as in normal chess notation.

    

   To Capture En Passant

   if you wish to capture one of SARGON's pawns using the en passant privilege, enter your pawn's move. After your pawn move is displayed, SARGON's pawn will blink and then vanish. When SARGON captures en peasant, his move is displayed on the graphics board in the same way. SARGON prints it in the move list as PxPep.

    

   To play another game after checkmate:

   If either your or SARGON is checkmated, and you wish to play againk just hit any key. The screen will blank out and SARGON will ask:

   "Care for Another Came?"

   Replies to this question are just like those to the original l"Care for a Game?"

    

   To resign a hopless game or take back a move:

   Ifyou decide your position is hopeless, or you wish to change a move entered in error, first wait until it is your turn to move. Then enter "control-R." You will immediately get the "Care for Another Game?" question. If you want to start over, type "y," but if you want to correct the board display, type "n." You will then get the routine that allows you to setup a board position.

    

   To setup or correct a board position: If you typed "n". a "Care for a Game" question, SARGON will now ask:

   "Would you like to analyse a position?"

   If you answer "n" to this one, you will be out of SARGON entirely and back in the computer's monitor state. An answer of "y" will display the board just as you left it. The lower left-hand corner will blink. That, your signal that you can change the contents of that square, using one of the analysis commands.

    

   Summary of Analysis Commands

   <:CR>
   A carriage return leaves the contents of the square unchanged and blinks the next square. If you are already at the upper right-hand corner, it wraps around to the lower left-hand corner and blink, that square.

   Backspace
   A backspace leaves the contents of the square unchanged and blinks.. square in the other direction. If, the opposite of a <:CR>, so you can go either direction.

   0
   An entry of 0, or of the space bar, or any key not listed in these commands will empty the square.

   "Enter a Piece"
   To enter a piece, type in piece-code, color-code, moved-code.

   Piece-code is a letter indicating the desired piece (upper or lower case):

   K -- King

   Q -- Queen

   R -- Rook

   B -- Bishop

   N -- Knight

   P -- Pawn

   Color-code is a letter indicating the side the piece belongs to (also upper or lower case):

   w -- white

   b -- black

   Moved-code is a number indicating whether the Piece has moved or not:

   0 - Piece has never moved

   1 - piece has moved

   Some examples:

   To enter a black pawn on its original square type:

   "P,b,0"

   A white knight in the middle of the board would be:

   "N,w,1"

   A black king on its original square which has however moved:

   "K,b,1"

   Escape
   The wscape key will terminate the blinking cycle. SARGON will ask:

   "Is this right?"

   An answer pf "n" wo;; gp bacl tp setting up the board. If you say "y" then SARGON will ask for information it needs to resume play from this point. The color chooice and search depth questions are the same as in Section 1. In addition SARGON must be given the answer to:

   "Whose move is it?"

    

   To terminate execution:

   The way out of the SARGON program depend, on whether you're at the end of a game, in the middle of a game, or setting up a board position.

   At the end of a game:

   1. Depress any key.
   2. SARGON responds with: "Care for Another Game?"
   3. Answer with "n."
   4. SARGON responds with: "Would you like to analyze a position?"
   5. Answer with "n" and you're out.

   In the middle of a game:

   1. Wait until it's your turn.
   2. Enter "Control-R"
   3. SARGON responds with: "Care for Another Game?"
   4. Follow 3-5 as for the end of a game.

   Setting up a board:

   1. Depress the escape key.
   2. SARGON answers: "R this right?"
   3. Respond with nswering four questions at once.
   4. Follow 2-4 as for the middle of a game.

 

Notes on the Implementation of SARGON

 

1. SARGON was assembled using the TDL Macro Assembler, which does not use the ZILOG mnemonics. Conversion to ZILOG mnemonic, can be performed on instruction for instruction basis using the conversion chart included with this listing.

    

2. I/0 is based on the JOVE operation system which runs en the Wave-Mate Jupiter III computer. For ease in conversion all I/0 has been isolated to the following areas: Accept Input Character (p. 82), I/O Macro Definitions (p. 68), and Set Up Empty Board (p. 89).

    

3. SARGON must be loaded at a start address which is an even 256 byte page boundary (that is, at an address of the form XXOO hexadecimal).

    

4. Graphics routines assume a 96 by 128 dot matrix with black characters on a white background. To convert to a display with white character, on a black background, only six lines of code need be changed:

Location	Is	Change to
DB04	MVI M,80H	MVI M,OBFH
DB08	MVI M,OBFH	MVI M,80H
2 lines above IP04	JRZ IP04	JRNZ IP04
4 lines above IP18	JRNZ IPI8	JRZ IP18
2 lines above IP18	JRNZ IP2C	JRZ IP2C
1 line below IP18	JRZ IP2C	JRNZ IP2C

1. SARGON requires a minimum of 8K bytes of memory available for user programs.

Image of page 19 for reference

;*******************************************************************************
;            SARGON
;
;	Sargon is a computer chess playing program designed and coded by Dan and 
; Kathe Spracklen,
; Copyright 1978. All rights reserved. No part of this publication may be 
; reproduced without the prior
; written permission.
;
;*******************************************************************************
; EQUATES
;*******************************************************************************
;
PAWN	=	1
KNIGHT	=	2
BISHOP	=	3
ROOK	a	4
QUEEN	=	5
KING	=	6
WHITE	-	0
BLACK	=	80H
BPAWN	-	BLACK+PAWN

;*******************************************************************************
; TABLES SECTION
;*******************************************************************************

START
	.LOC	START+80H
TBASE	=	START+100H

;*******************************************************************************
; DIRECT --	Direction Table. Used to determine the direction of movement of 
; each piece.
;*******************************************************************************

DIRECT	-	.-TBASE
	.BYTE	+09,+11,-11,-09
	.BYTE	+10,-10,+01,-01
	.BYTE	-21,-12,+08,+19
	.BYTE	+21,+12,-08,-19
	.BYTE	+10,+10,+11,+09
	.BYTE	-10,-10,-11,-09









Image of page 20 for reference





; *******************************************************
; DPOINT -- Direction Table. Pointer. Used to determine. 
; where to begin in the direction table for any 
; given piece.
; *******************************************************
DPOINT =	.-TBASE
.BYTE 20,16,8,0,4,0,0
; *******************************************************
; DCOUNT -- Direction Table Counter. Used to determine, 
; the number of directions of movement for any 
; given piece.
; *******************************************************
DCOUNT =	-TBASE 
.BYTE 4,4,8,4,4,8,8
; *******************************************************
; PVALUE -- Point Value. Gives the point value of each 
; piece, or the worth of each piece.
; *******************************************************
PVALUE =	.-TBASE-1
.BYTE 1,3,3,5,9,10
; *******************************************************
; PIECES -- The initial arrangement of the first rank of 
; pieces on the board. Use to set up the board 
; for the start of the game.
; *******************************************************
PIECES =	.-TBASE
.BYTE 4,2,3,5,6,3,2,4






Image of page 21 for reference





; *******************************************************
; BOARD	-- Board Array. Used to hold the current position 
; of the board during play. The board itself
; looks like: 
; 	FFFFFFFFFFFFFFFFFFFF 
; 	FFFFFFFFFFFFFFFFFFFF 
; 	FF0402030506030204FF 
; 	FF0101010101010101FF 
; 	FF0000000000000000FF 
; 	FF0000000000000000FF 
; 	FF0000000000000060FF 
; 	FF0000000000000000FF 
; 	FF8181818181818181FF 
; 	FF8482838586838284FF 
; 	FFFFFFFFFFFFFFFFFFFF 
; 	FFFFFFFFFFFFFFFFFFFF 
; The values of FF form the border of the 
; board, and are used to indicate when a piece 
; moves off the board. The individual bits of 
; the other bytes in the board array are as
; follows:
; 	Bit 7 -- Color of the piece
; 	1 -- Black 
; 	0 -- White 
; 	Bit 6 -- Not used 
; 	Bit 5 -- Not used 
; 	Bit 4 --Castle flag for Kings only
; 	Bit 3 -- Piece has moved flag
; 	Bits 2-0 Piece type 
; 		1 -- Pawn 
; 		2 -- Knight
; 		3 -- Bishop 
; 		4 -- Rook 
; 		5 -- Queen 
; 		6 -- King
; 		7 -- Not used
; 		0 -- Empty Square
; *******************************************************

BOARD = .-TBASE 
BOARDA: BLKB 120





Image of page 22 for reference





; *******************************************************
; ATKLIST -- Attack List. A two part array, the first
; 	half for white and the second half for black. 
; 	It is used to hold the attackers of any given 
; 	square in the order of their value.
; WACT	-- White Attack Count. This is the first
; 	byte of the array and tells how many pieces are 
; 	in the white portion of the attack list.
; BACT	-- Black Attack Count. This is the eighth byte of 
; 	the array and does the same for black.
; *******************************************************
WACT = ATKLST 
BACT = ATKLST+7 
ATKLST: WORD 0,0,0,0,0,0,0
; *******************************************************
; PLIST	-- Pinned Piece Array. This is a two part array. 
; 	PLISTA contains the pinned piece position. 
; 	PLISTD contains the direction from the pinned 
; 	piece to the attacker.
; *******************************************************
PLIST = .-TBASE-1 
PLISTD =	PLIST+10 
PLISTA: WORD 0,0,0,0,0,0,0,0,0,0
; *******************************************************
; POSK	-- Position of Kings. A two byte area, the first 
; 	byte of which hold the position of the white 
; 	king and the second holding the position of 
; 	the black king.
; POSQ	-- Position of Queens. Like POSK,but for queens.
; *******************************************************
POSK: BYTE 24,95 
POSQ: BYTE 14,94 
.BYTE -1




Image of page 23 for reference




; *******************************************************
; SCORE	-- Score Array. Used during Alpha-Beta pruning to 
; 	hold the scores at each ply. It includes two 
; 	"dummy" entries for ply -1 and ply 0.
; *******************************************************
SCORE: WORD 0,0,0,0,0,0
; *******************************************************
; PLYIX	-- Ply Table. Contains pairs of pointers, a pair 
; 	for each ply. The first pointer points to the 
; 	top of the list of possible moves at that ply. 
; 	The second pointer points to which move in the
; 	list is the one currently being considered.
; *******************************************************
PLYIX: WORD 0,0,0,0,0,0,0,0,0,0
.WORD 0,0,0,0,0,0,0,0,0,0
STACK	-- Contains the stack for the program.
.LOC START+2FFH
STACK:




Image of page 24 for reference




; *******************************************************
; TABLE INDICES SECTION
; Ml-M4	-- Working indices used to index into 
; 	the board array.
; Tl-T3	-- Working indices used to index into Direction 
; 	Count, Direction Value, and Piece Value tables.
; INDX1	-- General working indices. Used for various 
; INDX2 purposes.
; NPINS	-- Number of Pins. Count and pointer into the 
; 	pinned piece list.
; MLPTRI -- Pointer into the ply table which tells 
; 	which pair of pointers are in current use.
; MLPTRJ -- Pointer into the move list to the move that is 
; 	currently being processed.
:
; SCRIX -- Score Index. Pointer to the score table for 
; 	the ply being examined.
; BESTM	-- Pointer into the move list for the move that 
; 	is currently considered the best by the 
; 	Alpha-Beta pruning process.
; MLLST	-- Pointer to the previous move placed in the move 
; 	list. Used during generation of the move list.
; MLNXT	-- Pointer to the next available space in the move
; *******************************************************
.LOC START+O 
Ml: WORD TBASE 
M2: WORD TBASE
M3: WORD TBASE 
M4: WORD TBASE 
Tl: WORD TBASE 
T2: WORD TBASE 
T3: WORD TBASE 
INDX1: WORD TBASE 
INDX2: WORD TBASE 
NPINS: WORD TBASE 
MLPTRI: WORD PLYIX 
MLPTRJ: WORD 0
SCRIX: WORD 0 
BESTM: WORD 0 
MLLST: WORD 0 
MLNXT: WORD MLLST




Image of page 25 for reference




; *******************************************************
; VARIABLES SECTION
; KOLOR	-- Indicates computer's color. White is 0, and 
; 	Black is 80H.
; COLOR	-- Indicates color of the side with the move.
; P1-P3	-- Working area to hold the contents of the board 
; 	array for a given square.
; PMATE	-- The move number at which a checkmate is 
; 	discovered during look ahead.
; MOVENO -- Current move number.
; PLYMAX -- Maximum depth of search using Alpha-Beta 
; 	pruning.
; NPLY	-- Current ply number during Alpha-Beta
; 	pruning.
; CKFLG	-- A non-zero value indicates the king is in check.
; MATEF	-- A zero value indicates no legal moves.
; VALM	-- The score of the current move being examined. 
; BRDC	-- A measure of mobility equal to the total number 
; 	of squares white can move to minus the number 
; 	black can move to.
; PTSL	-- The maximum number of points which could be lost 
; 	through an exchange by the player not on the 
; 	move.
; PTSW1	-- The maximum number of points which could be won 
; 	through an exchange by the player not on the 
; 	move.
; PTSW2	-- The second highest number of points which could 
; 	be won through a different exchange by the player 
; 	not on the move.
; MTRL	-- A measure of the difference in material
; 	currently on the board. It is the total value of 
; 	the white pieces minus the total value of the 
; 	black pieces.
; BC0	-- The value of board control(BRDC) at ply 0.





Image of page 26 for reference





; MVO	-- The value of material(MTRL) at ply 0.
; PTSCK	-- A non-zero value indicates that the piece has 
; 	just moved itself into a losing exchange of 
; 	material.
; MOVES -- Our very tiny book of openings. Determines 
; 	the first move for the computer.
; *******************************************************
KOLOR: BYTE 0
COLOR: BYTE 0 
P1: BYTE 0 
P2: BYTE 0 
P3: BYTE 0 
PMATE: BYTE 0 
MOVENO: BYTE 0 
PLYMAX: BYTE 2 
NPLY: BYTE 0 
CKFLG: BYTE 0 
MATEF: BYTE 0 
VALM: BYTE 0 
BRDC: BYTE 0 
PTSL: BYTE 0 
PTSWl: BYTE 0 
PTSW2: BYTE 0 
MTRL: BYTE 0 
BCO: BYTE 0 
MVO: BYTE 0 
PTSCK: BYTE 0 
MOVES: BYTE 35,55,10H 
.BYTE 34,54,10H 
.BYTE 85,65,10H 
.BYTE 84,64,10H





Image of page 27 for reference





; *******************************************************
; MOVE LIST SECTION
; MUST	-- A 2048 byte storage area for generated moves. 
; 	This area must be large enough to hold all
; 		the moves for a single leg of the move tree.
; MLEND	-- The address of the last available location 
; 	in the move list.
; MLPTR	-- The Move List is a linked list of individual 
; 	moves each of which is 6 bytes in length. The 
; 	move list pointer(MLPTR) is the link field 
; 	within a move.
; MLFRP	-- The field in the move entry which gives the 
; 	board position from which the piece is moving.
; MLTOP	-- The field in the move entry which gives the 
; 	board position to which the piece is moving.
; MLFLG	-- A field in the move entry which contains flag 
; 	information. The meaning of each bit is as 
; 	follows:
; 		Bit 7 -- The color of any captured piece 
; 			0 -- White
; 			1 -- Black
; 		Bit 6 -- Double move flag (set for castling and 
; 			en passant pawn captures)
; 		Bit 5 -- Pawn Promotion flag; set when pawn 
; 			promotes.
; 		Bit 4 -- When set, this flag indicates that 
; 			this is the first move for the 
; 			piece on the move.
; 		Bit 3 -- This flag is set is there is a piece 
; 			captured, and that piece has moved at 
; 			least once.
; 		Bits 2-0	Describe the captured piece. A 
; 			zero value indicates no capture.
; 		MLVAL	-- The field in the move entry which contains the 
; 			score assigned to the move.
; *******************************************************




Image of page 28 for reference






.LOC START+300H 
MLIST: BLKB 2048 
MLEND = MLIST+2040 
MLPTR = 0 
MLFRP = 2 
MLTOP = 3 
MLFLG = 4 
MLVAL = 5



; *******************************************************
PROGRAM CODE SECTION
BOARD SETUP ROUTINE
FUNCTION:	To initialize the board array, setting the 
pieces in their initial positions for the 
start of the game.
CALLED BY: DRIVER
CALLS: None
ARGUMENTS: None
; *******************************************************
INITBD: MVI	B,120	; Pre-fill board with -1's 
LXI H,BOARDA
MVI M,-1 
INX H 
DJNZ .-3 
MVI B,8 
LXI X,BOARDA 
IB2:	MOV	A,-8(X)	; Fill non-border squares
MOV	21(X),A	; White pieces
SET	7,A	; Change to black
MOV	91(X),A	; Black pieces
MVI	31(X),PAWN	; White Pawns
MVI	81(X),BPAWN	; Black Pawns
MVI	41(X),0	; Empty squares 
MVI 51(X),0
MVI 61(X),0 
MVI 71(X),0 
INX X 
DJNZ IB2 
LXI	X,POSK	; Init King/Queen position list 
MVI 0(X),25
MVI 1(X),95 
MVI 2(X),24 
MVI 3(X),94 
RET






Image of page 29 for reference


 



; *******************************************************
; PATH ROUTINE
; *******************************************************
; FUNCTION:	To generate a single possible move for a given 
; 	piece along its current path of motion including:
; 	Fetching the contents of the board at the new 
; 	position, and setting a flag describing the 
; 	contents:
; 		0 -- New postion is empty
; 		1 -- Encountered a piece of the 
; 			opposite color
; 		2 -- Encountered a piece of the 
; 			same color
; 		3 -- New position is off the 
; 			board
; CALLED BY: MPIECE 
; 	ATTACK 
; 	PINFND
; CALLS: None
; ARGUMENTS: Direction from the direction array giving the 
; 	constant to be added for the new position.
; *******************************************************
PATH:	LXI	H,M2	; Get previous position 
MOV A,M
ADD	C	; Add diection constant
MOV	M,A	; Save new position
LIXD	M2	; Load board index
MOV	A,BOARD(X)	; Get contents of board
CPI	-1	; In boarder area ?
JRZ	PA2	; Yes - jump
STA	P2	; Save piece
ANI	7	; Clear flags
STA	T2	; Save piece type
RZ	; Return if empty	.
LDA	P2	; Get piece encountered
LXI	H,P1	; Get moving piece address
XRA	M	; Compare
BIT	7,A	; Do colors match ?
JRZ	PA1	; Yes - jump
MVI	A,1	; Set different color flag
RET	; Return
PA1:	MVI	A,2	; Set same color flag
RET	; Return
PA2:	MVI	A,3	; Set off board flag
RET	; Return








Image of page 30 for reference


 



; **********************************************************************
; 
; PIECE MOVER ROUTINE
; 
; FUNCTION:	To. generate all the possible legal moves for a given
; piece.
; 
; CALLED BY: GENMOV
; 
; CALLS:	PATH
; 	ADMOVE
; 	CASTLE
; 	ENPSNT
; 
; ARGUMENTS:	The piece to be moved.
; 
; **********************************************************************
MPIECE:	XRA	M ;	Piece to move
	ANI	87H ;	Clear flag bit
	CPI	BPAWN ;	Is is a black Pawn ?
	JRNZ	.+3 ;	No-Skip
	DCR	A ;	Decrement for black Pawns
	ANI	7 ;	Get piece type
	STA	T1 ;	Save piece type
	LIYD	T1 ;	Load index to DCOUNT/DPOINT
	MOV	B,DCOUNT(Y) ;	Get direction count
	MOV	A,DPOINT(Y) ;	Get direction pointer
	STA	INDX2 ;	Save as index to direct
	LIYD	INDX2 ;	Load index
MP5:	MOV	C,DIRECT(Y)	; Get move direction
	LDA	Ml	; From position
	STA	M2	; Initialize to position
MP10:	CALL	PATH	;	Calculate next position
	CPI	2	;	Ready for new direction ?
	JRNC	MP15	;	Yes - Jump
	ANA	A	;	Test for empty square
	EXAF		;	Save result
	LDA	T1	;	Get piece moved
	CPI	PAWN+1	;	Is it a Pawn ?
	JRC	MP20	;	Yes - Jump
	CALL	ADMOVE	;	Add move to list
	EXAF		;	Empty square ?
	JRNZ	MP15	;	No - Jump
	LDA	Tl	;	Piece type
	CPI	KING	;	King ?
	JRZ	MP15	:	Yes - Jump
	CPI	BISHOP	;	Bishop, Rook, or Queen ?
	JRNC	MP10	;	Yes - Jump
MP15:	INX	Y	;	Increment direction index
	DJNZ	MP5	;	Decr. count-jump if non-zerc
	LDA	T1	;	Piece type





Image of page 31 for reference


 


	CPI	KING ; King ?
	CZ	CASTLE ; Yes - Try Castling
	RET ; Return
; ***** PAWN LOGIC *****
MP20:	MOV	A,B ;	Counter for direction
	CPI	3 ;	On diagonal moves ?
	JRC	MP35 ;	Yes - Jump
	JRZ	MP30 ;	-or-jump if on 2 square move
	EXAF ;		Is forward square empty?
	JRNZ	MP15 ;	No - jump
	LDA	M2 ;	Get "to" position
	CPI	91 ;	Promote white Pawn ?
	JRNC	MP25 ;	Yes - Jump
	CPI	29 ;	Promote black Pawn ?
	JRNC	MP26 ;	No - Jump
MP25:	LXI	H,P2 ;	Flag address
	SET	5,M	; Set promote flag
MP26:	CALL	ADMOVE ;	Add to move list
	INX	Y ;	Adjust to two square move
	DCR	B
	LXI	H,P1 ;	Check Pawn moved flag
	BIT	3,M ;	Has it moved before ?
	JRZ	MP10 ;	No - Jump
	JMP	MP15 ;	Jump
MP30:	EXAF ;		Is forward square empty ?
	JRNZ	MP15 ;	No - Jump
MP31:	CALL	ADMOVE ;	Add to move list
	JMP	MP15 ;	Jump
MP35:	EXAF ;		Is diagonal square empty ?
	JRZ	MP36 ;	Yes - Jump
	LDA	M2 ;	Get "to" position
	CPI	91 ;	Promote white Pawn ?
	JRNC	MP37 ;	Yes - Jump
	CPI	29 ;	Black Pawn promotion ?
	JRNC	MP31 ;	No- Jump
MP37:	LXI	H,P2 ;	Get flag address
	SET	5,M ;	Set promote flag
	JMPR	MP31 ;	Jump
MP36:	CALL	ENPSNT ;	Try en passant capture
	JMP	MP15 ; 	Jump

 



Image of page 32 for reference


 

; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx**xxxxxxxxxxxxxxxxxxx
; 	EN PASSANT ROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To test for en passant Pawn capture and
; 		to add it to the move list if it is
; 		legal.
; CALLED BY:	--	MPIECE
; CALLS:	--	ADMOVE
; 
; ADJPTR
; 
; ARGUMENTS:	-- 	None
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
ENPSNT:	LDA	M1 ;	Set position of Pawn
	LXI	H,P1 ;	Check color
	BIT	7,M ;	Is it white ?
	JRZ	.+4 ;	Yes - skip
	ADI	10 ;	Add 10 for black
	CPI	61 ;	On en passant capture rank ?
	RNC ;		No - return
	CPI	69 ;	On en passant capture rank ?
	RNC ;		No - return
	LIXD	MLPTRJ ;	Get pointer to previous move
	BIT	4,MLFLG(X) ;	First move for that piece ?
	RZ ;		No - return
	MOV	A,MLTOP(X) ;	Get "to" postition
	STA	M4 ;	Store as index to board
	LIXD	M4 ;	Load board index
	MOV	A,BOARD(X) ;	Get piece moved
	STA	P3 ;	Save it
	ANI	7 ;	Get piece type
	CPI	PAWN ;	Is it a Pawn ?
	RNZ ;		No - return
	LDA	M4 ;	Get "to" position
	LXI	H,M2 ;	Get present "to" position
	SUB	M ;	Find difference
	JP	.+5 ;	Positive ? Yes - Jump
	NEG ;		Else take absolute value
	CPI	10 ;	Is difference 10 ?
	RNZ ;		No - return
	LXI	H,P2 ;	Address of flags
	SET	6,M ;	Set double move flag
	CALL	ADMOVE ;	Add Pawn move to move list
	LDA	M1 ;	Save initial Pawn position
	STA	M3
	LDA	M4 ;	Set "from" and "to" position8
			for dummy move







Image of page 33 for reference


 



STA	M1
STA	M2
LDA	P3	; Save captured Pawn
STA	P2
CALL	ADMOVE	; Add Pawn capture to move list
LDA	M3	; Restore "from" position
STA	M1

; **********************************************************************
; ADJUST MOVE LIST POINTER FOR DOUBLE MOVE
; 
; FUNCTION:	--	To adjust move list pointer to link around
; 		second move in double move.
; 
; CALLED BY: --	ENPSNT
; 	CASTLE
; 	(This mini-routine is not really called,
; 	but is jumped to to save time.)
; 
; CALLS:	-- 	None
; 
; ARGUMENTS:	-- 	None
; 
; **********************************************************************
ADJPTR:	LHLD	MLLST ;	Get list pointer
	LXI	D,-6 ;	Size of a move entry
	DAD	D ;	Back up list pointer
	SHLD	MLLST ;	Save list pointer
	MVI	M,0 ;	Zero out link, first byte
	INX	H ;	Next byte
	MVI	M,0 ;	Zero out link, second byte
	RET ; 		Return





Image of page 34 for reference


 

; **********************************************************************
; CASTLE ROUTINE
; 
; FUNCTION:	--	To determine whether castling is legal
; 		(Queen side, King side, or both) and add it
; 		to the move list if it is.
; 
; CALLED BY: -- MPIECE
; 
; CALLS:	--	ATTACK
; 		ADMOVE
; 		ADJPTR
; 
; ARGUMENTS:	-- 	None
; 
; **********************************************************************
CASTLE:	LDA	P1 ;	Get King
	BIT	3,A ;	Has it moved ?
	RNZ ;		Yes - return
	LDA	CKFLG ;	Fetch Check Flag
	ANA	A ;	Is the King in check ?
	RNZ ;		Yes - Return
	LXI	B,OFF03H ;	Initialize King-side values
CA5:	LDA	M1 ;	King position
	ADD	C ;	Rook position
	MOV	C,A ;	Save
	STA	M3 ;	Store as board index
	LIXD	M3 ;	Load board index
	MOV	A,BOARD(X) ;	Get contents of board
	ANI	7FH ;	Clear color bit
	CPI	ROOK ;	Has Rook ever moved ?
	JRNZ	CA20 ;	Yes - Jump
	MOV	A,C ;	Restore Rook position
	JMPR	CA15 ; 	Jump
CA10:	LIXD	M3 ;	Load board index
	MOV	A,BOARD(X) ;	Get contents of board
	ANA	A ;	Empty ?
	JRNZ	CA20 ;	No - Jump
	LDA	M3 ;	Current position
	CPI	22 ;	Wh.ite Queen Knight square ?
	JRZ	CA15 ;	Yes - Jump
	CPI	92 ;	Black Queen Knight square ?
	JRZ	CA15 ;	Yes - Jump
	CALL	ATTACK ;	Look for attack on square
	ANA	A ;	Any attackers ?
	JRNZ	CA20 ;	Yes - Jump
	LDA	M3 ;	Current position
CA15:	ADD	B ;	Next position
	STA	M3 ;	Save as board index
	LXI	H,M1 ;	King position
	CMP	M ;	Reached King ?







Image of page 35 for reference


 


	JRNZ	CA10 ;	No - jump
	SUB	B ;	Determine King's position
	SUB	B
	STA	M2 ;	Save it
	LXI	H,P2 ;	Address of flags
	MVI	M,40H ;	Set double move flag
	CALL	ADMOVE ;	Put king move in list
	LXI	H,M1 ;	Addr of King "from" position
	MOV	A,M ;	Get King's "from" position
	MOV	M,C ;	Store Rook "from" position
	SUB	B ;	Get Rook "to" position
	STA	M2 ;	Store Rook "to" position
	XRA	A ;	Zero
	STA	P2 ;	Zero move flags
	CALL	ADMOVE ;	Put Rook move in list
	CALL	ADJPTR ;	Re-adjust move list pointer
	LDA	M3 ;	Restore King position
	STA	M1 ;	Store
CA20:	MOV	AFB ;	Scan Index
	CPI	1 ;	Done ?
	RZ ;		Yes - return
	LXI	B,01FCH ;	Set Queen-side initial values
	JMP	CA5 ; 	Jump






Image of page 36 for reference


 


; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	ADMOVE ROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To add a move to the move list
; 
; CALLED BY: --	MPIECE
; 	ENPSNT
; 	CASTLE
; 
; CALLS:	--	None
; 
; ARGUMENT:	-- 	None
; **x***x*x*xx*xxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
ADMOVE:	LDED	MLNXT	; Addr of next loc in move list
	LXI	H,MLEND	; Address of list end
	ANA	A	; Clear carry flag
	DSBC	D	; Calculate difference
	JRC	AM10	; Jump if out of space
	LHLD	MLLST	; Addr of prev. list area
	SDED	MLLST	; Savn next as previous
	MOV	M,E	; Store link address
	INX	H
	MOV	M,D
	LXI	H,Pl	; Address of moved piece
	BIT	3,M	; Has it moved before ?
	JRNZ	.+7	; Yes - jump
	LXI	H,P2	; Address of move flags
	SET	4,M	; Set first move flag
	XCHG		; Address of move area
	MVI	M,0	; Store zero in link address
	INX	H
	MVI	M,0
	INX	H
	LDA	Ml	; Store "from" move position
	MOV	M,A
	INX	H
	LDA	M2	; Store "to" move position
	MOV	M,A
	INX	H
	LDA	P2	; Store move flags/capt. piece
	MOV	M,A
	INX	H
	MVI	M,0	; Store initial move value
	INX	H
	SHLD	MLNXT	; Save address for next move
	RET		; Return
AM10:	MVI	M,0	; Abort entry on table ovflow
	INX	H
	MVI	M,0
	DCX	H
	RET





Image of page 37 for reference


 



; **xxxxxx*x**xxxxx*xxx*xxxx*xxx*xxxxxxxxxxxx*xxxxxxxxxxxxx*xx
; 	GENERATE MOVE ROUTINE
; xxx*xx*x**xxxxxxx**xxxxxxxxx**x***x**xx*x*xx***x*x**x*xxxx*x
; FUNCTION:	--	To generate the move set for all of the
; 		pieces of a given color.
; CALLED BY:	--	FNDMOV
; CALLS:	--	MIECE
; 		INCHK
; ARGUMENTS:	--	None
; xxxxxxxxxxxxxxx*x*xxxx*xxxx*xxxx*xx*xxxxxxx*xxxxxxxxxx***x*x
GENMOV:	CALL	INCHK	; Test for King in check
	STA	CKFLG	; Save attack count as flag
	LDED	MLNXT	; Addr of next avail list space
	LHLD	MLPTRI	; Ply list pointer index
	INX	H	; Increment to next ply
	INX	H
	MOV	M,E	; Save move list pointer
	INX	H
	MOV	M,D
	INX	H
	SHLD	MLPTRI	; Save new index
	SHLD	MLLST	; Last pointer for chain init.
	MVI	A,21	; First position on board
GM5:	STA	M1 ;	Save as index
	LIXD	Ml ;	Load board index
	MOV	A,BOARD(X) ;	Fetch board contents
	ANA	A ;	Is it empty ?
	JRZ	GM10 ;	Yes - Jump
	CPI	-1 ;	Is it a boarder square ?
	JRZ	GM10 ;	Yes - Jump
	STA	P1 ;	Save piece
	LXI	H,COLOR ;	Address of color of piece
	XRA	M ;	Test color of piece
	BIT	7,A ;	Match ?
	CZ	MPIECE ;	Yes - call Move Piece
GM10:	LDA	M1 ;	Fetch current board position
	INR	A ;	Incr to next board position
	CPI	99 ;	End of board array ?
	JNZ	GM5 ;	No - Jump
	RET ; 		Return





Image of page 38 for reference


 

; xxxxxxxxxxxxxxxxxxxxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	CHECK ROUTINE
; xxxx*xxxxxxxxxxxxxxx-x*x*xxxxxxxxxxxxxx*xxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To determine whether or not the
; 		King is in check.
; CALLED BY:	--	GENMOV
; 		FNDMOV
; 		EVAL
; CALLS:	--	ATTACK
; 
; ARGUMENTS:	--	Color of King
; x****xxx*xs**xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
INCHK:	LDA	COLOR ;	Get color
INCHK1:	LXI	H,POSK ;	Addr of white King position
	ANA	A ;	White ?
	JRZ	.+3 ;	Yes - Skip
	INX	H ;	Addr of black King position
	MOV	A,M ;	Fetch King position
	STA	M3 ;	Save
	LIXD	M3 ;	Load board index
	MOV	A,BOARD(X) ;	Fetch board contents
	STA	P1 ;	Save
	ANI	7 ;	Get piece type
	STA	T1 ;	Save
	CALL	ATTACK ;	Look for attackers on King
	RET ; 		Return



Image of page 39 for reference

 

; ************************************************************
; ATTACK ROUTINE
; **************************************************************

; FUNCTION:	--	To find all attackers on a given square
; 		by scanning outward from the square
; 		until a piece is found that attacks
; 		that,square, or a piece is found that
; 		doesn't attack that square, or the edge
; 		of the board is reached.
; 
; 	In determining which pieces attack a square,
; this routine also takes into account the ability of
; certain pieces to attack through another attacking
; piece. (For example a queen lined up behind a bishop
; of her same color along a diagonal.) The bishop is
; then said to be transparent to the queen, since both
; participate in the attack.
; 
; 	In the case where this routine is called by
; CASTLE or INCHK, the routine is terminated as soon as
; an attacker of the opposite color is encountered.
; 
; CALLED BY: --	POINTS
; 	PINFND
; 	CASTLE
; 	INCHK
; 
; CALLS:	--	PATH
; 		ATKSAV
; 
; ARGUMENTS:	-- 	None
; **************************************************************
ATTACK:	PUSH	B ;	Save Register B
	XRA	A ;	Clear
	MVI	B,16 ;	Initial direction count
	STA	INDX2 ;	Initial direction index
	LIYD	INDX2 ;	Load index
AT5:	MOV	C,DIRECT(Y) ;	Get direction
	MVI	D,0 ;	Init. scan count/flags
	LDA	M3 ;	Init. board start position
	STA	M2 ; 	Save
AT10:	INR	D ;	Increment scan count
	CALL	PATH ;	Next position
	CPI	1 ;	Piece of a opposite color ?
	JRZ	AT14A ;	Yes - jump
	CPI	2 ;	Piece of same color ?
	JRZ	AT14B ;	Yes - jump

 

Image of page 40 for reference



	ANA	A	;	Empty position ?
	JRNZ	AT12	;	No - jump
	MOV	A,B	;	Fetch direction count
	CPI	9	;	On knight scan ?
	JRNC	AT10	;	No - jump
AT12:	INX	Y	;	Increment direction index
	DJNZ	AT5	;	Done ? No - jump
	XRA	A	;	No attackers
AT13:	POP	B	;	Restore register B
	RET		;	Return
AT14A:	BIT	6,D	;	Same color found already ?
	JRNZ	AT12	;	Yes - jump
	SET	5,D	;	Set opposite color found flag
	JMP	AT14	;	Jump
AT14B:	BIT	5,D	;	Opposite color found already?
	JRNZ	AT12	;	Yes - jump
	SET	6,D	;	Set same color found flag

; ***** DETERMINE IF PIECE ENCOUNTERED ATTACKS SQUARE *****
AT14:	LDA	T2 ;	Fetch piece type encountered
	MOV	E,A ;	Save
	MOV	A,B ;	Get direction-counter
	CPI	9 ;	Look for Knights ?
	JRC	AT25 ;	Yes - jump
	MOV	A,E ;	Get piece type
	CPI	QUEEN ;	Is is a Queen ?
	JRNZ	AT15 ;	No - Jump
	SET	7,D ;	Set Queen found flag
	JMPR	AT30 ;	Jump
AT15:	MOV	A,D ;	Get flag/scan count
	ANI	OFH ;	Isolate count
	CPI	1 ;	On first position ?
	JRNZ	AT16 ;	No - jump
	MOV	A,E ;	Get encountered piece type
	CPI	KING ;	Is it a King ?
	JRZ	AT30 ;	Yes - jump
AT16:	MOV	A,B ;	Get direction counter
	CPI	13 ;	Scanning files or ranks ?
	JRC	AT21 ;	Yes - jump
	MOV	A,E ;	Get piece type
	CPI	BISHOP ;	Is it a Bishop ?
	JRZ	AT30 ;	Yes - jump
	MOV	A,D ;	Get flags/scan count
	ANI	OFH ;	Isolate count
	CPI	1 ;	On first position ?
	JRNZ	AT12 ;	No - jump
	CMP	E ;	Is it a Pawn ?
	JRNZ	AT12 ;	No - jump
	LDA	P2 ;	Fetch piece including color


Image of page 41 for reference


	BIT	7,A ;	Is it white ?
	JRZ	AT20 ;	Yes - jump
	MOV	A,B ;	Get direction counter
	CPI	15 ;	On a non-attacking diagonal ?
	JRC	AT12 ;	Yes - jump
	JMPR	AT30 ;	Jump
AT20:	MOV	A,B ;	Get direction counter
	CPI	15 ;	On a non-attacking diagonal ?
	JRNC	AT12 ;	Yes - jump
	JMPR	AT30 ;	Jump
AT21:	MOV	A,E ;	Get piece type
	CPI	ROOK ;	Is is a Rook ?
	JRNZ	AT12 ;	No - jump
	JMPR	AT30 ;	Jump
AT25:	MOV	A,E ;	Get piece type
	CPI	KNIGHT ;	Is it a Knight ?
	JRNZ	AT12 ;	No - jump
AT30:	LDA	T1 ;	Attacked piece type/flag
	CPI	7 ;	Call from POINTS ?
	JRZ	AT31 ;	Yes - jump
	BIT	5,D ;	Is attacker opposite color ?
	JRZ	AT32 ;	No - jump
	MVI	A,1 ;	Set attacker found flag
	JMP	AT13 ;	Jump
AT31:	CALL	ATKSAV ;	Save attacker in attack list
AT32:	LDA	T2 ;	Attacking piece type
	CPI	KING ;	Is it a King,?
	JZ	AT12 ;	Yes - jump
	CPI	KNIGHT ;	Is it a Knight ?
	JZ	AT12 ;	Yes - jump
	JMP	AT10 ; 	Jump



Image of page 42 for reference




; *************************************************************
; ATTACK SAVE ROUTINE
; *************************************************************
; FUNCTION: --	To save an attacking piece value in the attack
; list, and to increment the attack count for that
; color piece.
; 
; The pin piece list is checked for the attacking
; piece, and if found there, the piece is not
; included in the attack list.
; 
; CALLED BY: -- ATTACK
; 
; CALLS:	-- 	PNCK
; 
; ARGUMENTS:	-- 	None
; *************************************************************
ATKSAV:	PUSH	B ;	Save Regs BC
	PUSH	D ;	Save Regs DE
	LDA	NPINS ;	Number of pinned pieces
	ANA	A ;	Any ?
	CNZ	PNCK	; yes - check pin list
	LIXD	T2 ;	Init index to value table
	LXI	H,ATKLST ;	Init address of attack list
	LXI	B,0 ;	Init increment for white
	LDA	P2 ;	Attacking piece
	BIT	7,A ;	Is it white ?
	JRZ	.+4 ;	Yes - jump
	MVI	C,7 ;	Init increment for black
	ANI	7 ;	Attacking piece type
	MOV	E,A ;	Init increment for type
	BIT	7,D ;	Queen found this scan ?
	JRZ	.+4 ;	No - jump
	MVI	E,QUEEN ;	Use Queen slot in attack list
	DAD	B ;	Attack list address
	INR	M ;	Increment list count
	MVI	D,0
	DAD	D ;	Attack list slot address
	MOV	A,M ;	Get data already there
	ANI	OFH ;	Is first slot empty ?
	JRZ	AS20 ;	Yes - jump
	MOV	A,M ;	Get data again
	ANI	OFOH ;	Is second slot empty ?
	JRZ	AS19 ;	Yes - jump
	INX	H ;	Increment to King slot
	JMPR	AS20 ;	Jump
AS19:	RLD ;		Temp save lower in upper
	MOV	A,PVALUE(X) ;	Get new value for attack list
	RRD ;		Put in 2nd attack list slot
	JMPR	AS25 ;	Jump
AS20:	MOV	A,PVALUE(X) ;	Get new value for attack list
	RLD ;		Put in 1st attack list slot


Image of page 43 for reference



AS25:	POP	D	; Restore DE regs
POP	B ; Restore BC regs
RET ; Return

; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	PIN CHECK ROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	Checks to see if the attacker is in the
; 		pinned piece list. If so he is not a valid
; 		attacker unless the direction in which he
; 		attacks in the same as the direction along
; 		which he is pinned. If the piece is
; 		found to be invalid as an attacker, the
; 		return to the calling routine is aborted
; 		and this routine returns directly to ATTACK.
; 
; CALLED BY: -- ATKSAV
; 
; CALLS:	-- 	None
; 
; ARGUMENTS: --	The direction of the attack. The
; pinned piece counnt.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*
PNCK:	MOV	D,C	; Save attack direction
	MVI	E,0	; Clear flag
	MOV	C,A	; Load pin count for search
	MVI	B,0
	LDA	M2	; Position of piece
	LXI	H,PLISTA	; Pin list address
PCl:	CCIR		; Search list for position
	RNZ		; Return if not found
	EXAF		; Save search paramenters
	BIT	0,E	; Is this the first find ?
	JRNZ	PC5	; No - jump
	SET	0,E	; Set first find flag
	PUSH	H	; Get corresp index to dir list
	POP	X
	MOV	A,9(X)	; Get direction
	CMP	D	; Same as attacking direction ?
	JRZ	PC3	; Yes - jump
	NEG		; Opposite direction ?
	CMP	D	; Same as attacking direction ?
	JRNZ	PC5	; No - jump
PC3:	EXAF		; Restore search parameters
	JPE	PC1	; Jump if search not complete
	RET		; Return
PC5:	POP	PSW	; Abnormal exit
	POP	D	; Restore regs.
	POP	B
	RET		; Return to ATTACK


Image of page 44 for reference


; .*x**xxxxtcxx*xxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	PIN FIND ROUTINE
; .xxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*
; FUNCTION:	--	To produce a list of all pieces pinned
; 		against the King or Queen, for both white
; 		and black.
; CALLED BY:	--	FNDMOV
; 		EVAL
; CALLS:	--	PATH
; 		ATTACK
; ARGUMENTS:	--	None
; .xxxxxxxxx***x*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
PINFND: XRA	A	; Zero pin count
	STA	NPINS
	LXI	D,POSK	; Addr of King/Queen pos list
PF1:	LDAX	D	; Get position of royal piece
	ANA	A	; Is it on board ?
	JZ	PF26	; No- jump
	CPI	-1	; At end of list ?
	RZ		; Yes return
	STA	M3	; Save position as board index
	LIXD	M3	; Load index to board
	MOV	A,BOARD(X)	; Get contents of board
	STA	P1	; Save
	MVI	B,8	; Init scan direction count
	XRA	A
	STA	INDX2	; Init direction index
	LIYD	INDX2
PF2:	LDA	M3	; Get King/Queen position
	STA	M2	; Save
	X RA	A
	STA	M4	; Clear pinned piece saved pos
	MOV	C,DIRECT.(Y)	; Get direction of scan
PF5:	CALL	PATH	; Compute next position
	ANA	A	; Is it empty ?
	JRZ	PF5	; Yes - jump
	CPI	3	; Off board ?
	JZ	PF25	; Yes - jump
	CPI	2	; Piece of same color found ?
	LDA	M4	; Load pinned piece position
	JRZ	PF15	; Yes - jump
	ANA	A	; Possible pin ?
	JZ	PF25	; No - jump
	LDA	T2	; Piece type encountered
	CPI	QUEEN	; Queen ?
	JZ	PF19	; Yes - jump
	MOV	L,A	; Save piece type


Image of page 45 for reference

	MOV	A,B	; Direction counter
	CPI	5	; Non-diagonal direction ?
	JRC	PF10	; Yes - jump
	MOV	A,L	; Piece type
	CPI	BISHOP	; Bishop ?
	JNZ	PF25	; No - jump
	JMP	PF20	; Jump
PF10:	MOV	A,L	; Piece type
	CPI	ROOK	; Rook ?
	JNZ	PF25	; No - jump
	JMP	PF20	; Jump
PF15:	ANA	A	; Possible pin ?
	JNZ	PF25	; No - jump
	LDA	M2	; Save possible pin position
	STA	M4
	JMP	PF5	; Jump
PF19:	LDA	P1	; Load King or Queen
	ANI	7	; Clear flags
	CPI	QUEEN	; Queen ?
	JRNZ	PF20	; No - jump
	PUSH	B	; Save regs.
	PUSH	D
	PUSH	Y
	XRA	A	; Zero out attack list
	MVI	B,14
	LXI	H,ATKLST
	MOV	M,A
	INX	H
	DJNZ	.-2
	MVI	A,7	; Set attack flag
	STA	T1
	CALL	ATTACK	; Find attackers/defenders
	LXI	H,WACT	; White queen attackers
	LXI	D,BACT	; Black queen attackers
	LDA	P1	; Get queen
	BIT	7,A	; Is she white ?
	JRZ	.+3	; Yes - skip
	XCHG		; Reverse for black
	MOV	A,M	; Number of defenders
	XCHG		; Reverse for attackers
	SUB	M	; Defenders minus attackers
	DCR	A	; Less 1
	POP	Y	; Restore regs.
	POP	D
	POP	B
	JP	PF25	; Jump if pin not valid
PF20:	LXI	H,NPINS	; Address of pinned piece count
	INR	M	; Increment
	LIXD	NPINS	; Load pin list index
	MOV	PLISTD(X),C	; Save direction of pin



Image of page 46 for reference



	LDA	M4 ;	Position of pinned piece
	MOV	PLIST(X),A ;	Save in list
PF25:	INX	Y ;	Increment direction index
	DJNZ	PF27 ;	Done ? No - Jump
PF26:	INX	D ;	Incr King/Queen pos index
	JMP	PF1 ;	Jump
PF27:	JMP	PF2 ; 	Jump



Image of page 47 for reference

; *************************************************************
; EXCHANGE ROUTINE
; *************************************************************
; FUNCTION:	--	To determine the exchange value of a
; 		piece on a given square by examining all
; 		attackers and defenders of that piece.
; 
; CALLED BY: -- POINTS
; 
; CALLS:	-- 	NEXTAD
; 
; ARGUMENTS:	-- 	None.
; 
; *************************************************************
XCHNG:		EXX		; Swap regs.
		LDA	P1	; Piece attacked
		LXI	H,WACT	; Addr of white attkrs/dfndrs
		LXI	D,BACT	; Addr of black attkrs/dfndrs
	.BIT	7,A	; Is piece white ?
		JRZ	.+3	; Yes - jump
		XCHG		; Swap list pointers
		MOV	B,M	; Init list counts
		XCHG
		MOV	C,M
		XCHG
		EXX		; Restore regs.
		MVI	C,0	; Init attacker/defender flag
		MVI	E,0	; Init points lost count
		LIXD	T3	; Load piece value index
		MOV	D,PVALUE(X)	; Get attacked piece value
		SLAR	D	; Double it
		MOV	B,D	; Save
		CALL	NEXTAD	; Retrieve first attacker
		RZ		; Return if none
XC10:		MOV	L,A	; Save attacker value
		CALL	NEXTAD	; Get next defender
		JRZ	XC18	; Jump if none
		EXAF		; Save defender value
		MOV	A,B	; Get attacked value
		CMP	L	; Attacked less than attacker ?
		JRNC	XC19	; No - jump
		EXAF		; -Restore defender
XC15:		CMP	L	; Defender less than attacker ?
		RC		; Yes - return
		CALL	NEXTAD	; Retrieve next attacker value
		RZ		; Return if none
		MOV	L,A	; Save attacker value
		CALL	NEXTAD	; Retrieve next defender value
		JRNZ	XC15	; Jump if none
XC18:		EXAF		; Save Defender
		MOV	A,B	; Get value of attacked piece



Image of page 48 for reference


XC19:	BIT	0,C ;	Attacker or defender ?
	JRZ	.+4 ;	Jump if defender
	NEG ;		Negate value for attacker
	ADD	E ;	Total points lost
	MOV	E,A ;	Save total
	EXAF ;		Restore previous defender
	RZ ;		Return if none
	MOV	B,L ;	Prev attckr becomes defender
	JMP	XC10 ; 	Jump

; *************************************************************
; NEXT ATTACKER/DEFENDER ROUTINE
; *************************************************************
; FUNCTION:	--	To retrieve the next attacker or defender
; 		piece value from the attack list, and delete
; 		that piece from the list.
; 
; CALLED BY: -- XCHNG
; 
; CALLS:	-- 	None
; 
; ARGUMENTS: --	Attack list addresses.
; 	Side flag
; 	Attack list counts
; 
; *************************************************************
NEXTAD:	INR	C	; Increment side flag
	EXX		; Swap registers
	MOV	A,B	; Swap list counts
	MOV	B,C
	MOV	C,A
	XCHG		; Swap list pointers
	XRA	A
	CMP	B	; At end of list ?
	JRZ	NX6	; Yes - jump
	DCR	B	; Decrement list count
	INX	H	; Increment list	inter
	CMP	M	; Check next item in list
	JRZ	.-2	; Jump if empty
	RRD		; Get value from list
	ADD	A	; Double it
	DCX	H	; Decrement list pointer
NX6:	EXX ; Restore regs.
	RET ; Return



Image of page 49 for reference


; *************************************************************
; 	POINT EVALUATION ROUTINE
; *************************************************************
; FUNCTION:	--	To perform a static board evaluation and
; 				derive a score for a given board position
; 	CALLED BY:		--		FNDMOV
; 					EVAL
; 	CALLS:		--		ATTACK
; 					XCHNG
; 					LIMIT
; 	ARGUMENTS:		-- 		None
; *************************************************************
POINTS:	XRA	A	; Zero out variables
	STA	MTRL
	STA	BRDC
	STA	PTSL
	STA	PTSWI
	STA	PTSW2
	STA	PTSCK
	LXI	H,T1	; Set attacker flag
	MVI	M,7
	MVI	A,21	; Init to first square on board
PT5:	STA	M3	; Save as board index
	LIXD	M3	; Load board index
	MOV	A,BOARD(X)	; Get piece from board
	CPI	-1	,Off board edge ?
	JZ	PT25	; Yes - jump
	LXI	H,P1	; Save piece, if any
	MOV	M,A
	ANI	7	; Save piece type, if any
	STA	T3
	CPI	KNIGHT	; Less than a Knight (Pawn) ?
	JRC	PT6X	; Yes - Jump
	CPI	ROOK	; Rook, Queen or King ?
	JRC	PT6.B	; No - jump
	CPI	KING	; Is it a King ?
	JRZ	PT6AA	; Yes - jump
	LDA	MOVENO	; Get move number
	CPI	7	; Less than 7 ?
	JRC	PT6A	; Yes - Jump
	JMP	PT6X	; Jump
PT6AA:	BIT	4,M	; Castled yet ?
	JRZ	PT6A	; No - jump
	MVI	A,+6	; Bonus for castling
	BIT	7,M	; Check piece color
	JRZ	PT6D	; Jump if white
	MVI	A,-6	; Bonus for black castling




Image of page 50 for reference


	JMP	PT6D	; Jump
PT6A:	BIT	3,M	; Has piece moved yet ?
	JRZ	PT6X	; No - jump
	JMP	PT6C	; Jump
PT6B:	BIT	3,M	; Has piece moved yet ?
	JRNZ	PT6X	; Yes - jump
PT6C:	MVI	A,-2	; Two point penalty for white
	BIT	7,M	; Check piece color
	JRZ	.+4	; Jump if white
	MVI	A,+2	; Two point penalty for black
PT6D:	LXI	H,BRDC	; Get address of board control
	ADD	M	; Add on penalty/bonus points
	MOV	M,A	; Save
PT6X:	XRA	A	; Zero out attack list
	MVI	B,14
	LXI	H,ATKLST
	MOV	M,A
	INX 	H
	DJNZ	.-2
	CALL	ATTACK	; Build attack list for square
	LXI	H,BACT	; Get black attacker count addr
	LDA	WACT	; Get white attacker count
	SUB	M	; Compute count difference
	LXI	H,BRDC	; Address of board control
	ADD	M	; Accum board control score
	MOV	M,A	; Save
	LDA	P1	; Get piece on current square
	ANA	A	; Is it empty ?
	JZ	PT25	; Yes - jump
	CALL	XCHNG	; Evaluate exchange, if any
	XRA	A	; Check for a loss
	CMP	E	; Points lost ?
	JRZ	PT23	; No - Jump
	DCR	D	; Deduct half a Pawn value
	LDA	P1	; Get piece under attack
	LXI	H,COLOR	; Color of side just moved
	XRA	M	; Compare with piece
	BIT	7,A	; Do colors match ?
	MOV	A,E	; Points lost
	JRNZ	PT20	; Jump if no match
	LXI	H,PTSL	; Previous max points lost
	CMP	M	; Compare to current value
	JRC	PT23	; Jump if greater than
	MOV	M,E	; Store new value as max lost
	LIXD	MLPTRJ	; Load pointer to this move
	LDA	M3	; Get position of lost piece
	CMP	MLTOP(X)	; Is it the one moving ?
	JRNZ	PT23	; No - jump
	STA	PTSCK	; Save position as a flag
	JMP	PT23	; Jump




Image of page 51 for reference


PT20:	LXI	H,PTSW1 ;	Previous maximum points won
	CMP	M ;	Compare to current value
	JRC	.+4 ;	Jump if greater than
	MOV	A,M ;	Load previous max value
	MOV	M,E ;	Store new value as max won
	LXI	H,PTSW2 ;	Previous 2nd max points won
	CMP	M ;	Compare to current value
	JRC	PT23 ;	Jump if greater than
	MOV	M,A ;	Store as new 2nd max lost
PT23:	LXI	H,Pl ;	Get piece
	BIT	7,M ;	Test color
	MOV	A,D ;	Value of piece
	JRZ	.+4 ;	Jump if white
	NEG ;		Negate for black
	LXI	H,MTRL ;	Get addrs of material total
	ADD	M ;	Add new value
	MOV	M,A ;	Store
PT25:	LDA	M3 ;	Get current board position
	INR	A ;	Increment
	CPI	99 ;	At end of board ?
	JNZ	PT5 ;	No - jump
	LDA	PTSCK ;	Moving piece lost flag
	ANA	A ;	Was it lost ?
	JRZ	PT25A ;	No - jump
	LDA	PTSW2 ;	2nd max points won
	STA	PTSW1 ;	Store as max points won
	XRA	A ;	Zero out 2nd max points won
	STA	PTSW2
PT25A:	LDA	PTSL ;	Get max points lost
	ANA	A ;	Is it zero ?
	JRZ	.+3 ;	Yes - jump
	DCR	A ;	Decrement it
	MOV	B,A ;	Save it
	LDA	PTSW1 ;	Max,points won
	ANA	A ;	Is it zero ?
	JRZ	.+11. ;	Yes - jump
	LDA	PTSW2 ;	2nd max points won
	ANA	A ;	Is it zero ?
	JRZ	.+5 ;	Yes - jump
	DCR	A ;	Decrement it
	SRLR	A ;	Divide it by 2
	SUB	B ;	Subtract points lost
	LXT	9,COLOR ;	Color of side just moved
	BIT	7,M ;	Is it white ?
	JRZ	.+4 ;	Yes - jump
	NEG ;		Negate for black
	LXI	H,MTRL ;	Net material on board
	ADD	M ;	Add exchange adjustments
	LXI	H,MVO ;	Material at ply 0




Image of page 52 for reference


	SUB	M ;	Subtract from current
	MOV	B,A ;	Save
	MVI	A,30 ;	Load material limit
	CALL	LIMIT ;	Limit to plus or minus value
	MOV	E,A ;	Save limited value
	LDA	BRDC ;	Get board control points
	LXI	H,BCO ;	Board control at ply zero
	SUB	M ;	Get difference
	MOV	B,A ;	Save
	LDA	PTSCK ;	Moving piece lost flag
	ANA	A ;	Is it zero ?
	JRZ	.+4 ;	Yes - jump
	MVI	B,0 ;	Zero board control points
	MVI	A,6 ;	Load board control limit
	CALL	LIMIT ;	Limit to plus or minus value
	MOV	D,A ;	Save limited value
	MOV	A,E ;	Get material points
	ADD	A ;	Multiply by 4
	ADD 	A
	ADD	D ;	Add board control
	LXI	H,COLOR ;	Color of side just moved
	BIT	7,M ;	Is it white ?
	JRNZ	.+4 ;	No - jump
	NEG ;		Negate for white
	ADI	80H ;	Rescale score (neutral = 80H
	STA	VALM ;	Save score
	LIXD	MLPTRJ ;	Load move list pointer
	MOV	MLVAL(X),A ;	Save score in move list
	RET ; 		Return




Image of page 53 for reference

; xxx*xxxxx*x*xxxxxxxxxxxxxxxx**xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	LIMIT ROUTINE
; ~*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	FUNCTION:	--	To limit the magnitude of a given value
; 			to another given value.
; 	CALLED BY:	--	POINTS
; 	CALLS:	--	None
; 	ARGUMENTS:	--	Input	- Value, to be limited in the B
; 					register.
;.					- Value to limit to in the A register
; 			Output - Limited value in the A register.
; **xx*******xxxxx**xxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*xxxxxxx
LIMIT:	BIT	7,B	; Is value negative ?
	JZ	LIM10	; No - jump
	NEG		; Make positive
	CMP	B	; Compare to limit
	RNC		; Return if outside limit
	MOV	A,B	; Output value as is
	RET		; Return
LIM10:	CMP	B	; Compare to limit
	RC		; Return if outside limit
	MOV	A,B	; Output value as is
	RET
	Return
.END




Image of page 54 for reference


; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
	MOVE ROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To execute a move from the move list on the
; 		board array.
; CALLED BY:	--	CPTRMV
; 		PLYRMV
; 		EVAL
; 		FNDMOV
; 		VALMOV
; CALLS:	--	None
; 
; ARGUMENTS:	-- 	None
; xxxxxxxxxxx*xxxxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
MOVE:	LHLD	MLPTRJ	; Load move list pointer
	INX	H	; Increment past link bytes
	INX	H
MV1:	MOV	A,M	; "From" position
	STA	M1	; Save
	INX	H	; Increment pointer
	MOV	A,M	; "To" position
	STA	M2	; Save
	INX	H	; Increment pointer
	MOV	D,M	; Get captured piece/flags
	LIXD	M1	; Load "from" pos board index
	MOV	E,BOARD(X)	; Get piece moved
	BIT	5,D	; Test Pawn promotion flag
	JRNZ	MV15	; Jump if set
	MOV	A,E	; Piece moved
	ANI	7	; Clear flag bits
	CPI	QUEEN	; Is it a queen ?
	JRZ	MV20	; Yes - jump
	CPI	KING	; Is it a king ?
	JRZ	MV30	; Yes - jump
MV5:	LIYD	M2	; Load "to" pos board index
	SET	3,E	; Set piece moved flag
	MOV	BOARD(Y),E	; Insert piece at new position
	MVI	BOARD(X),0	; Empty previous position
	BIT	6,D	; Double move ?
	JRNZ	MV40	; Yes - jump
	MOV	A,D	; Get captured piece, if any
	ANI	7
	CPI	QUEEN	; Was it a queen ?
	RNZ		; No - return
	LXI	H,POSQ	; Addr of saved Queen position
	BIT	7,D	; Is Queen white ?
	JRZ	MV10	; Yes - jump
	INX	H	; Increment to black Queen pos



Image of page 55 for reference


MV10:	XRA	A	; Set saved position to zero
	MOV	M,A
	RET		; Return
MV15:	SET	2,E	; Change Pawn to a Queen
	JMP	MV5	; Jump
MV20:	LXI	H,POSQ	; Addr of saved Queen position
MV21:	BIT	7,E	; Is Queen white ?
	JRZ	MV22	; Yes - jump
MV22:	LDA	M2	; Get rnewnQueenbpositionen pos
	MOV	M,A	; Save
	JMP	MV5	; Jump
MV30:	LXI	H,POSK	; Get saved King position
	BIT	6,D	; Castling ?
	JRZ	MV21	; No - jump
	SET	4,E	; Set King castled flag
	JMP	MV21	; Jump
MV40:	LHLD	MLPTRJ	; Get move list pointer
	LXI	D,8	; Increment to next move
	DAD	D
	JMP	MV1	; Jump (2nd part of dbl move)




Image of page 56 for reference

; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'xxxxx
; UN-MOVE ROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To reverse the process of the move routine,
; 		thereby restoring the board array to its
; 		previous position.
; CALLED BY:	--	VALMOV
; 		EVAL
; 		FNDMOV
; 		ASCEND
; CALLS:	--	None
; 
; ARGUMENTS:	-- 	None
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
UNMOVE:	LHLD	MLPTRJ	; Load move list pointer
	INX	H	; Increment past link bytes
	INX	H
UM1:	MOV	A,M ;	Get "from" position
	STA	Ml ;	Save
	INX	H ;	Increment pointer
	MOV	A,M ;	Get "to" position
	STA	M2 ;	Save
	INX	H ;	Increment pointer
	MOV	D,M ;	Get captured piece/flags
	LIXD	M2 ;	Load "to" pos board index
	MOV	E,BOARD(X) ;	Get piece moved
	BIT	5,D ;	Was it a Pawn promotion ?
	JRNZ	UM15 ;	Yes - jump
	MOV	A,E ;	Get piece moved
	ANI	7 ;	Clear flag bits
	CPI	QUEEN ;	Was it a Queen ?
	JRZ	UM20 ;	Yes - jump
	CPI	KING ;	Was it a King ?
	JRZ	UM30 ;	Yes - jump
UM5:	BIT	4,D ;	Is this 1st move for piece ?
	JRNZ	UM16 ;	Yes - jump
UM6:	LIYD	M1 ;	Load "from" pos board index
	MOV	BOARD(Y),E ;	Return to previous board pos
	MOV	A,D ;	Get captured piece, if any
	ANI	8FH ;	Clear flags
	MOV	BOARD(X),A ;	Return to board
	BIT	6,D ;	Was it a double move ?
	JRNZ	UM40 ;	Yes - jump
	MOV	A,D ;	Get captured piece, if any
	ANI	7 ;	Clear flag bits
	CPI	QUEEN ;	Was it a Queen ?
	RNZ ;		No - return




Image of page 57 for reference


	LXI	H,POSQ	;	Address of saved Queen pos
	BIT	7,D	;	Is Queen white ?
	JRZ	UM10	;	Yes - jump
	INX	H	;	Increment to black Queen pos
UM10:	LDA	M2	;	Queen's previous position
	MOV	M,A	;	Save
	RET		;	Return
UM15:	RES	2,E	;	Restore Queen to Pawn
	JMP	UM5	;	Jump
UM16:	RES	3,E	;	Clear piece moved flag
	JMP	UM6	;	Jump
UM20:	LXI	H,POSQ	;	Addr of saved Queen position
UM21:	BIT	7,E	;	Is Queen white ?
	JRZ	UM22	;	Yes - jump
	INX	H	;	Increment to black Queen pos
UM22:	LDA	M1	;	Get previous position
	MOV	M,A	;	Save
	JMP	UM5	;	Jump
UM30:	LXI	H,POSK	;	Address of saved King pos
	BIT	6,D	;	Was it a castle ?
	JRZ	UM21	;	No - jump
	RES	4,E	;.	Clear castled flag
	JMP	UM21	;	Jump
UM40:	LHLD	MLPTRJ	;	Load move list pointer
	LXI	D,8	;	Increment to next move
	DAD	D
	JMP	UM1	;	Jump (2nd part of dbl move)




Image of page 58 for reference


; ********************************************************
; SORT ROUTINE
; ********************************************************
; FUNCTION:	--	To sort the move list in order of
; 		increasing move value scores.
; 
; CALLED BY: -- FNDMOV
; 
; CALLS:	-- 	EVAL
; 
; ARGUMENTS:	-- 	None
; ********************************************************
SORTM:	LBCD	MLPTRI	; Move list begin pointer
	LXI	D,0	; Initialize working pointers
SR5:	MOV	H,B
	MOV	L,C
	MOV	C,M	; Link to next move
	INX	H
	MOV	B,M
	MOV	M,D	; Store to link in list
	DCX	H
	MOV	M,E
	XRA	A	; End of list ?
	CMP	B
	RZ		; Yes - return
SR10:	SBCD	MLPTRJ	; Save list pointer
	CALL	EVAL	; Evaluate move
	LHLD	MLPTRI	; Begining of move list
	LBCD	MLPTRJ	; Restore list pointer
SR15:	MOV	E,M	; Next move for compare
	INX	H
	MOV	D,M
	XRA	A	; At end of list ?
	CMP	D
	JRZ	SR25	; Yes - jump
	PUSH	D	; Transfer move pointer
	POP	X
	LDA	VALM	; Get new move value
	CMP	MLVAL(X)	; Less than list value ?
	JRNC	SR30	; No - jump
SR25:	MOV,	M,B	; Link new move into list
	DCX	H
	MOV	M,C
	JMP	SR5	; Jump
SR30:	XCHG		; Swap pointers
	JMP	SR15	; Jump




Image of page 59 for reference


; xxxx*xxx***xxxxx**xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; EVALUATION ROUTINE
; *x*rt*xxxx*xxx*xx*xxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To evaluate a given move in the move list.
; 		It first makes the move on the board, then ii
; 		the move is legal, it evaluates it, and then
; 		restores the boaard position.
; CALLED BY:	--	SORT
; CALLS:	--	MOVE
; 		INCHK
; 		PINFND
; 		POINTS
; 		UNMOV
; ARGUMENTS:	--	None
; **x**x*xxx**xxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
EVAL:	CALL	MOVE ;	Make move on the board array
	CALL	INCHK ;	Determine if move is legal
	ANA	A ;	Legal move ?
	JRZ	EV5 ;	Yes - jump
	XRA	A ;	Score of zero
	STA	VALM ;	For illegal move
	JMP	EV10 ;	Jump
EV5:	CALL	PINFND ;	Compile pinned list
	CALL	POINTS ;	Assign points to move
EV10:	CALL	UNMOVE ;	Restore board array
	RET ; 		Return


Image of page 60 for reference

; ******************************************************************
; FIND MOVE ROUTINE
; ******************************************************************
; 
; FUNCTION:	--	To determine the computer's best move by
; 		performing a depth first tree search using
; 		the techniques of alpha-beta pruning.
; 
; CALLED BY: -- CPTRMV
; 
; CALLS:	--	PINFND
; 		POINTS
; 		GENMOV
; 		SORTM
; 		ASCEND
; 		UNMOV
; 
; ARGUMENTS:	-- 	None
; 
; ******************************************************************
FNDMOV:	LDA	MOVENO	; Currnet move number
	CPI	1	; First move ?
	CZ	BOOK	; Yes - execute book opening
	XRA	A	; Initialize ply number to zer
	STA	NPLY
	LXI	H,0	; Initialize best move to zero
	SHLD	BESTM
	LXI	H,MLIST	; Initialize ply list pointers
	SHLD	MLNXT
	LXI	H,PLYIX-2
	SHLD	MLPTRI
	LDA	KOLOR	; Initialize color
	STA	COLOR
	LXI	H,SCORE	; Initialize score index
	SHLD	SCRIX
	LDA	PLYMAX	; Get max ply number
	ADI	2	; Add 2
	MOV	B,A	; Save as counter
	XRA	A	; Zero out score table
	MOV	M,A
	INX	H
	DJNZ	.-2
	STA	BC0	; Zero ply 0 board control
	STA	MV0	; Zero ply 0 material
	CALL	PINFND	; Complie pin list
	CALL	POINTS	; Evaluate board at ply 0
	LDA	BRDC	; Get board control points
	STA	BC0	; Save
	LDA	MTRL	; Get material count
	STA	MV0	; Save
FM5:	LXI	H,NPLY	; Address of ply counter
	INR	M	; Increment ply count






Image of page 61 for reference

	XRA	A	; Initialize mate flag
	STA	MATEF
	CALL	GENMOV	; Generate list of moves
	LDA	NPLY	; Current ply counter
	LXI	H,PLYMAX	; Address of maximum ply number
	CMP	M	; At max ply ?
	CC	SORTM	; No - call sort
	LHLD	MLPTRI	; Load ply index pointer
	SHLD	MLPTRJ	; Save as last move pointer
FM15:	LHLD	MLPTRJ	; Load last move pointer
	MOV	E,M	; Get next move pointer
	INX	H
	MOV	D,M
	MOV	A,D
	ANA	A	; End of move list ?
	JRZ	FM25	; Yes - jump
	SDED	MLPTRJ	; Save current move pointer
	LHLD	MLPTRI	; Save in ply pointer list
	MOV	M,E
	INX	H
	MOV	M,D
	LDA	NPLY	; Current ply counter
	LXI	H,PLYMAX	; Maximum ply number ?
	CMP	M	; Compare
	JRC	FM18	; Jump if not max
	CALL	MOVE	; Execute move on board array
	CALL	INCHK	; Check for legal move
	ANA	A	; Is move legal
	JRZ	.+8	; Yes - jump
	CALL	UNMOVE	; Restore board position
	JMP	FM15	; Jump
	LDA	NPLY	; Get ply counter
	LXI	H,PLYMAX	; Max ply number
	CMP	M	; Beyond max ply ?
	JRNZ	FM35	; Yes - jump
	LDA	COLOR	; Get current color
	XRI	80H	; Get opposite color
	CALL	INCHK1	; Determine if King is in check
	ANA	A	; In check ?
	JRZ	FM35	; No - jump
	JMP	FM19	; Jump (One more ply for check)
FM18:	LIXD	MLPTRJ	; Load move pointer
	MOV	A,MLVAL(X)	; Get move score
	ANA	A	; Is it zero (illegal move) ?
	JRZ	FM15	; Yes - jump
	CALL	MOVE	; Execute move on board array
FM19:	LXI	H,COLOR	; Toggle color
	MVI	A,80H
	X RA	M
	MOV	M,A	; Save new color



Image of page 62 for reference




	BIT	7,A	; Is it white ?
	RNZ	.+6	; No - jump
	XI	H,MOVENO	; Increment move number
	NR	M
	HLD	SCRIX	; Load score table pointer
	OV	A,M	; Get score two plys above
	NX	H	; Increment to current ply
	NX	H
	OV	M,A	; Save score as initial value
	CX	H	; Decrement pointer
	HLD	SCRIX	; Save it
	MP	FM5	; Jump
FM25:	LDA	MATEF ;	Get mate flag
	ANA	A ;	Checkmate or stalemate ?
	JRNZ	FM30 ;	No - jump
	LDA	CKFLG ;	Get check flag
	ANA	A ;	Was King in check ?
	MVI	A,80H ;	Pre-set stalemate score
	JRZ	FM36 ;	No - jump (stalemate)
	LDA	MOVENO ;	Get move number
	STA	MATE	;	Save
	MVI	A,OFFH	;	Pre-set checkmate score
	JMP	FM36	;	Jump
FM30:	LDA	NPLY	;	Get ply counter
	CPI	1	;	At top of tree ?
	RZ		;	Yes - return
	CALL	ASCEND	;	Ascend one ply in tree
	LHLD	SCRIX	;	Load score table pointer
	INX	H	;	Increment to current ply
	INX	H
	MOV	A,M	;	Get score
	DCX	H	;	Restore pointer
	DCX	H
	JMP	FM37	;	Jump
FM35:	CALL	PINFND	;	Compile pin list
	CALL	POINTS	;	Evaluate move
	CALL	UNMOVE	;	Restore board position
	LDA	VALM	;	Get value of move
FM36:	LXI	H,MATEF	;	Set mate flag
	SET	0,M
	LHLD	SCRIX	;	Load score table pointer
FM37:	CMP	M	;	Compare to score 2 ply above
	JRC	FM40	;	Jump if less
	JRZ	FM40	;	Jump if equal
	NEG		;	Negate score
	INX	H	;	Incr score table pointer
	CMP	M	;	Compare to score 1 ply above
	JC	FM15	;	Jump if less than
	JZ	FM15	;	Jump if equal



Image of page 63 for reference




	MOv	M,A ;	Save as new score 1 ply above
	LDA	NPLY ;	Get current ply counter
	CPI	1 ;	At top of tree ?
	JNZ	FM15 ;	No - jump
	LHLD	MLPTRJ ;	Load current move pointer
	SHLD	BESTM ;	Save as best move.pointer
	LDA	SCORE+1 ;	Get best move score
	CPI	OFFH ;	Was it a checkmate ?
	JNZ	FM15 ;	No - jump
	LXI	H,PLYMAX ;	Get maximum ply number
	DCR	M ;	Subtract 2
	DCR	M
	LDA	KOLOR ;	Get computer's color
	BIT	7,A ;	Is it white ?
	RZ ;		Yes - return
	LXI	H,PMATE ;	Checkmate move number
	DCR	M ;	Decrement
	RET ;		Return
FM40:	CALL	ASCEND ;	Ascend one ply in tree
	JMP	FM15 ; 	Jump



Image of page 64 for reference




; ******************************************************************
; ASCEND TREE ROUTINE
; ******************************************************************
; 
; FUNCTION:	--	To adjust all necessary parameters to
; 		ascend one ply in the tree.
; 
; CALLED BY: -- FNDMOV
; 
; CALLS:	-- 	UNMOV
; 
; ARGUMENTS:	-- 	None
; ******************************************************************

ASCEND:	LXI	H,COLOR	; Toggle color
	MVI	A,80H
	XRA	M
	MOV	M,A	; Save new color
	BIT	7,A	; Is it white ?
	JRZ	.+6	; Yes - jump
	LXI	H,MOVENO	; Decrement move number
	DCR	M
	LHLD	SCRIX	; Load score table index
	DCX	H	; Decrement
	SHLD	SCRIX	; Save
	LXI	H,NPLY	; Decrement ply counter
	DCR	M
	LHLD	MLPTRI	; Load ply list pointer
	DCX	H	; Load pointer to move list to
	MOV	D,M
	DCX	H
	MOV	E,M
	SDED	MLNXT	; Update move list avail ptr
	DCX	H	; Get ptr to next move to undo
	MOV	D,M
	DCX	H
	MOV	E,M
	SHLD	MLPTRI	; Save new ply list pointer
	SDED	MLPTRJ	; Save next move pointer
	CALL	UNMOVE	; Restore board to previous pl
	RET		; Return



Image of page 65 for reference



; ******************************************************************
; ONE MOVE BOOK OPENING
; *****************************************x***************
; FUNCTION:	--	To provide an opening book of a single
; 		move.
; 
; CALLED BY: -- FNDMOV
; 
; CALLS:	-- 	None
; 
; ARGUMENTS:	-- 	None
; ******************************************************************

BOOK:	POP	PSW	; Abort return to FNDMOV
	LXI	H,SCORE+1	; Zero out score
	MVI	M,0	; Zero out score table
	LXI	H,BMOVES-2	; Init best move ptr to book
	SHLD	BESTM
	LXI	H,BESTM	; Initialize address of pointer
	LDA	KOLOR	; Get computer's color
	ANA	A	; Is it white ?
	JRNZ	BM5	; No - jump
	LDAR		; Load refresh reg (random no)
	BIT	0,A	; Test random bit
	RZ		; Return if zero (P-K4)
	INR	M	; P-Q4
	INR	M
	INR	M
	RET		; Return
BM5:	INR	M	; Increment to black moves
	INR	M
	INR	M
	INR	M
	INR	M
	INR	M
	LIXD	MLPTRJ	; Pointer to opponents 1st move
	MOV	A,MLFRP(X)	; Get "from" position
	CPI	22	; Is it a Queen Knight move ?
	JRZ	BM9	; Yes - Jump
	CPI	27	;.Is it a King Knight move ?
	JRZ	BM9	; Yes - jump
	CPI	34	; Is it a Queen Pawn ?
	JRZ	BM9	; Yes - jump
	RC		; If Queen side Pawn opening -
			;	return (P-K4)
	CPI	35	; Is it a King Pawn ?
	RZ		; Yes - return (P-K4)
BM9:	INR	M	;	(P-Q4)
	INR	M
	INR	M
	RET		; Return to CPTRMV

; **x*********x*****x**x*xx*xx*xxxxxxxxxxxxxxxxxx*xxxxxxxxxxx


Image of page 66 for reference





; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*xxxxxxxx
; 	GRAPHICS DATA BASE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; DESCRIPTION:	The Graphics Data Base contains the
; 	necessary stored data to propuce the piece
; 	on the board. Only the center 4 x 4 blocks are
; 	stored and only for a Black Piece on a White
; 	square. A White piece on a black square is
; 	produced by complementing each block, and a
; 	piece on its own color square is produced
; 	by moving in a kernel of 6 blocks.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
	.LOC	START+384
BLBASE	=	START+512
BLOCK	=	.-BLBASE
	.RADIX	16
	.BYTE	80,80,80,80	; Black Pawn on White square
	.BYTE	80,0A0,90,80
	.BYTE	80,0AF,9F,80
	.BYTE	80,83,83,80
	.BYTE	80,0B0,0B0,80	; Black Knight on White square
	.BYTE	OBE,0BF,0BF,95
	.BYTE	OA0,0BE,0BF,85
	.BYTE	83,83,83,81
	.BYTE	80,0A0,00,80	; Black Bishop on White square
	.BYTE	OA8,0BF,0BD,80
	.BYTE	82,0AF,87,80
	.BYTE	82,83,83,80
	.BYTE	80,80,80,80	; Black Rook on White square
	.BYTE	8A,0BE,0BD,85
	.BYTE	80,0BF,0BF,80
	.BYTE	82,83,83,81
	.BYTE	90,80,80,90	; Black Queen on White square
	.BYTE	OBF,0B4,0BE,95
	.BYTE	8B,0BF,9F,81
	.BYTE	83,83,83,81
	.BYTE	80,088,90,80	; Black King on White square
	.BYTE	OBC,0BA,0B8,94
	.BYTE	OAF,0BF,0BF,85
	.BYTE	83,83,83,81
	.BYTE	90,0B0,0B0,80	; Toppled Black King
	.BYTE	OBF,0BF,0B7,80
	.BYTE	9F,0BF,0BD,80
	.BYTE	80,80,88,9D
KERNEL =	.-BLBASE
	.BYTE	OBF,9F,0AF,0BF,9A,0A5	; Pawn Kernel
	.BYTE	89,0AF,0BF,9F,0B9,9F	; Knight Kernel
	.BYTE	97,0BE,96,0BD,9B,0B9	; Bishop Kernel
	.BYTE	0B5,0A1,92,0BF,0AA,95	; Rook Kernel
	.BYTE	OA8,9B,0B9,0B6,0AF,0A7	; Queen Kernel
	.BYTE	OA3,85,0A7,9A,0BF,9F	; King Kernel
	.BYTE	0A8,0BF,89,0A2,8F,86	; Toppled King Kernel
	.RADIX	10


Image of page 67 for reference




; ******************************************************************
; 	STANDARD MESSAGES
;  ********************tr********tt********trtt*trtt,etttt**tr**xtr,ttt
	.LOC	START+1800H
GRTTNG: .ASCII "WELCOME TO CHESS! CARE FOR A GAME?"
ANAMSG: .ASCII "WOULD YOU LIKE TO ANALYZE A POSITION?"
CLRMSG: .ASCII	"DO YOU WANT TO PLAY WHITE(w) OR BLACK(b)?"
TITLEl: .ASCII	"SARGON"
TITLE2: .ASCII	"PLAYER"
SPACE:  .ASCII	"	; For output of blank area
MVENUM: .ASCII	"01 "
TITLES: .ASCII	" "
	.ASCII	[^H83]	; Part of TITLE 3 - Underlines
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	" "
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	[^H83]
	.ASCII	" "
MVEMSG:	.ASCII	"al-al"
0.0:	.ASCII	"0-0 "
0.0.0:	.ASCII	"0-0-0"
CKMSG:	.ASCII	"CHECK"
MTMSG:	.ASCII	"MATE IN "
MTPL:	.ASCII	"2"
PCs:	.ASCII	"KQRBNP"	; Valid piece characters
UWIN:	.ASCII	"YOU WIN"
IWIN:	.ASCII	"I WIN"
AGAIN:	.ASCII	"CARE FOR ANOTHER GAME?"
CRTNES: .ASCII "IS THIS RIGHT?"
PLYDEP:	.ASCII	"SELECT LOOK AHEAD (1-6)"
TITLE4:	-.ASCII	"	"
WSMOVE:	.ASCII	"WHOSE MOVE IS IT?"
BLANKR:	.ASCII	["HlC]		; Control-
P.PEP:	.ASCII	"PxPep"
INVALI:	.ASCII	"INVALID MOVE"
INVAL2:	.ASCII	"TRY AGAIN"



Image of page 68 for reference



; ******************************************************************
; VARIABLES
; ******************************************************************
BRDPOS:	.BLKB	1 ;	Index into the board array
ANBDPS:	.BLKB	1 ;	Additional index required for ANALYS
INDXER:	.WORD	BLBASE ;	Index into graphics data base
NORMAD:	.BLKW	1 ;	The address of the upper left hand
			corner of the square on the board
LINECT:	.BYTE	0 ;	Current line number

; ******************************************************************
; MACRO DEFINITIONS
; ******************************************************************
; All input/output to SARGON is handled in the form of macro calls to
; simplify conversion to alternate systems. All of the input/output macros
; conform to the Jove monitor of the Jupiter III computer.
; ******************************************************************
;*** OUTPUT  ***
	.DEFINE	CARRET=
	[RST	7
	.BYTE	92H,lAH
	.WORD 	0]
;*** CLEAR SCREEN ***
	.DEFINE	CLRSCR=
	[RST	7
	.BYTE	OB2H,lAH
	.WORD 	BLANKR,1]
;*** PRINT ANY LINE (NAME, LENGTH) ***
	.DEFINE	PRTLIN[NAME,LNGTH)=
	[RST	7
	.BYTE	0B2H,lAH
	.WORD 	NAME,LNGTH]
;*** PRINT ANY BLOCK (NAME, LENGTH) ***
	.DEFINE	PRTBLK[NAME,LNGTH]=
	[RST	7
	.BYTE	OB3H,lAH
	.WORD 	NAME,LNGTH]
;*** EXIT TO MONITOR ***
	.DEFINE	EXIT=
	[RST	7
	.BYTE 	01FH)



Image of page 69 for reference



; ******************************************************************
; MAIN PROGRAM DRIVER
; ***********************************************************
; FUNCTION:	--	To coordinate the game moves.
; 
; CALLED BY: -- None
; 
; CALLS:	--	INTERR
; 		INITBD
; 		DSPBRD
; 		CPTRMV
; 		PLYRMV
; 		TBCPCL
; 		PGIFND
; MACRO CALLS:		CLRSCR
; 		CARRET
; 		PRTLIN
; 		PRTBLK
; ARGUMENTS:		None
; **********************************************************
	.LOC	START+lA00H ;	Above the move logic
DRIVER:	LXI	SP,STACK ;	Set stack pointer
	CLRSCR ;		Blank out screen
	PRTLIN	GRTTNG,34 ;	Output greeting
DRIV01:	CALL	CHARTR	; Accept answer
	CARRET		; New line
	CPI	59H	; Is it a 'Y' ?
	JNZ	ANALYS	; Yes - jump
	SUB	A	; Code of White is zero
	STA	COLOR	; White always moves first
	CALL	INTERR	; Players color/search depth
	CALL	INITBD	; Initialize board array
	MVI	A,1	; Move number is 1 at at start
	STA	MOVENO	; Save
	STA	LINECT	; Line number is one at start
	LXI	H,MVENUM	; Address of ascii move number
	MVI	M,30H	; Init to '01 '
	INX	H
	MVI	M,31H
	INX	H
	MVI	M,20H
	CALL	DSPBRD	; Set up graphics board
	PRTLIN	TITLE4,15	; Put up player headings
	PRTLIN	TITLE3,15
DRIV04:	PRTBLK	MVENUM,3	; Display move number
	LDA	KOLOR	; Bring in computer's color
	ANA	A	; Is it white ?
	JRNZ	DR08	; No - jump



Image of page 70 for reference





	CALL	PGIFND ;	New page if needed
	CPI	1 ;	Was page turned ?
	CZ	TBCPCL ;	Yes - Tab to computers column
	CALL	CPTRMV ;	Make and write computers move
	PRTBLK	SPACE,1 ;	Output a space
	CALL	PLYRMV ;	Accept and make players move
	CARRET ;		New line
	JMPR	DROC ;	Jump
DR08:	CALL	PLYRMV ;	Accept and make players move
	PRTBLK	SPACE,1 ;	Output a space
	CALL	PGIFND ;	New page if needed
	CPI	1 ;	Was page turned ?
	CZ	TBCPCL ;	Yes - Tab to computers column
	CALL	CPTRMV ;	Make and write computers move
	CARRET ;		New line
DROC:	LXI	H,MVENUM+2 ;	Addr of 3rd char of move
	MVI	A,20H ;	Ascii space
	CMP	M ;	Is char a space ?
	MVI	A,3AH ;	Set up test value
	JRZ	DR10 ;	Yes - jump
	INR	M ;	Increment value
	CMP	M ;	Over Ascii 9 ?
	JRNZ	DR14 ;	No - jump
	MVI	M,30H ;	Set char to zero
DR10:	DCX	H ;	2nd char of Ascii move no.
	INR	M ;	Increment value
	CMP	M ;	Over Ascii 9 ?
	JRNZ	DR14 ;	No - jump
	MVI	M,30H ;	Set char to zero
	DCX	H ;	1st char of Ascii move no.
	INR	M ;	Increment value
	CMP	M ;	Over Ascii 9 ?
	JRNZ	DR14 ;	No - jump
	MVI	M,31H ;	Make 1st char a one
	MVI	A,30H ;	Make 3rd char a zero
	STA	MVENUM+2
DR14:	LXI	H,MOVENO ;	Hexadecimal move number
	INR	M ;	Increment
	JMP	DRIV04 ; 	Jump




Image of page 71 for reference



; **************************************************************
; INTERROGATION FOR PLY & COLOR
; **************************************************************
; FUNCTION:	--	To query the player for his choice of ply
; 		depth and color.
; 
; CALLED BY: -- DRIVER
; 
; CALLS:	-- 	CHARTR
; 
; MACRO CALLS:	PRTLIN
; 	CARRET
; 
; ARGUMENTS:	-- 	None




Image of page 72 for reference





; **************************************************************
 INTERR: PRTLIN	CLRMSG,41	; Request color choice
 	CALL	CHARTR	; Accept response
 	CARRET		; New line
	CPI	57H	; Did player request white ?
	JRZ	IN04	; Yes - branch
	SUB	A	; Set computers color to white
	STA	KOLOR
	LXI	H,TITLE1	; Prepare move list titles
	LXI	D,TITLE4+2
	LXI	B,6
	LDIR
	LXI	H,TITLE2
	LXI	D,TITLE4+9
	LXI	B,6
	LDIR
	JMPR	IN08	; Jump
IN04:	MVI	A,80H	; Set computers color to black
	STA	KOLOR
	LXI	H,TITLE2	; Prepare move list titles
	LXI	D,TITLE4+2
	LXI	B,6
	LDIR
	LXI	H,TITLEI
	LXI	D,TITLE4+9
	LXI	B,6
	LDIR
IN08:	PRTLIN	PLYDEP,23	; Request depth of search
	CALL	CHARTR ;	Accept response
	CARRET ;		New line
	LXI	H,PLYMAX ;	Address of ply depth variabl
	MVI	M,2 ;	Default depth of search
	CPI	31H ;	Under minimum of 1 ?
	RM ;		Yes - return
	CPI	37H ;	Over maximum of 6 ?
	RP ;		Yes - return
	SUI	30H ;	Subtract Ascii constant
	MOV	M,A ;	Set desired depth
	RET ; 		Return




Image of page 73 for reference






; **************************************************************
; COMPUTER MOVE ROUTINE
; ***********************************************************
; FUNCTION:	--	To control the search for the computers move
; 		and the display of that move on the board
; 		and in the move list.
; 
; CALLED BY: -- DRIVER
; 
; CALLS:	--	FNDMOV
; 		FCDMAT
; 		MOVE
; 		EXECMV
; 		BITASN
; 		INCHK
; MACRO CALLS:		PRTBLK
; 		CARRET
; 
; ARGUMENTS:	-- 	None
***********************************************************
CPTRMV:	CALL	FNDMOV ;	Select best move
	LHLD	BESTM ;	Move list pointer variable
	SHLD	MLPTRJ ;	Pointer to move data
	LDA	SCORE+1 ;	To check for mates
	CPI	1 ;	Mate against computer ?
	JRNZ	CPOC ;	No - jump
	MVI	C,1 ;	Computer mate flag
	CALL	FCDMAT ;	Full checkmate ?
CPOC:	CALL	MOVE ;	Produce move on board array
	CALL	EXECMV ;	Make move on graphics board
			and return info about it
	MOV	A,B ;	Special move flags
	ANA	A ;	Special ?
	JRNZ	CP10 ;	Yes - jump
	MOV	D,E ;	"To" position of the move
	CALL	BITASN ;	Convert to Ascii
	S.HLD	MVEMSG+3 ;	Put in move message
	MOV	D,C ;	"From" position of the move
	CALL	BITASN ;	Convert to Ascii
	SHLD	MVEMSG ;	Put in move message
	PRTBLK	MVEMSG,5 ;	Output text of move
	JMPR	CPlC ;	Jump
CP10:	BIT	1,B ;	King side castle ?
	JRZ	.+11 ;	No - jump
	PRTBLK	0.0,5 ;	Output "0-O"
	JMPR	CPlC ;	Jump
	BIT	2,B ;	Queen side castle ?
	JRZ	.+11 ;	No - jump




Image of page 74 for reference



	PRTBLK	0.0.0,5	;  Output "O-O-O"
	JMPR	CPlC	; Jump
	PRTBLK	P.PEP,5	; Output "PxPep" - En passant
CPlC:	LDA	COLOR	; Should computer call check ?
	MOV	B,A
	XRI	80H	; Toggle color
	STA	COLOR
	CALL	INCHK	; Check for check
	ANA	A	; Is enemy in check ?
	MOV	A,B	; Restore color
	STA	COLOR
	JRZ	CP24	; No - return
	CARRET		; New line
	LDA	SCORE+1	; Check for player mated
	CPI	OFFH	; Forced mate ?
	CNZ	TBCPMV	; No - Tab to computer column
	PRTBLK CKMSG,5	; Output "check"
	LXI	H,LINECT ;	Address of screen line count
	INR	M ;	Increment for message
CP24:	LDA	SCORE+1 ;	Check again for mates
	CPI	OFFH ;	Player mated ?
	RNZ ;		No - return
	MVI	C,0 ;	Set player mate flag
	CALL	FCDMAT ;	Full checkmate ?
	RET ; 		Return




Image of page 75 for reference





; *xxxxxxxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 		FORCED MATE HANDLING
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx~xxxxxx
; FUNCTION:	--	To examine situations where there exits
; 		a forced mate and determine whether or
; 		not the current move is checkmate. If it is,
; 		a losing player is offered another game,
; 		while a loss for the computer signals the
; 		King to tip over in resignation.
; CALLED BY:	--	CPTRMV
; CALLS:	--	MATED
; 		CHARTR
; 		TBPLMV
; ARGUMENTS:	--	The only value passed in a register is the
; 		flag which tells FCDMAT whether the computer
; 		or the player is mated.
; xxxxxxxxxxxx*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
FCDMAT:	LDA	MOVENO	; Current move number
	MOV	B,A	; Save
	LDA	PMATE	; Move number where mate occurs
	SUB	B	; Number of moves till mate
	ANA	A	;Checkmate ?
	JRNZ	FMOC	; No - jump
	BIT	0,C	; Check flag for who is mated
	JRZ	FM04	; Jump if player
	CARF9T		; New line
	PRTLIN	CKMSG,9	; Print "CHECKMATE"
	CALL	MATED	; Tip over King
	PRTLIN	UWIN,7	; Output "YOU WIN"
	JMPR	FM08	; Jump
FM04:	PRTLIN	MTMSG,4	; Output "MATE"
	PRTLIN	IWIN,5	; Output "I WIN"
FM08:	POP	H	; Remove return addresses
	POP	H
	CALL	CHARTR	; Input any char to play again
FM09:	CLRSCR		; Blank screen
	PRTLIN	AGAIN,22		"CARE FOR ANOTHER GAME?"
	JMP	DRIV01	; Jump (Rest of game init)
FMOC:	BIT	0,C	; Who has forced mate ?
	RNZ		; Return if player
	CARRET		; New line
	ADI	30H	; Number of moves to Ascii
	STA	MTPL	; Place value in message
	PRTLIN	MTMSG,9	; Output "MATE IN x MOVES"
	CALL	TBPLMV	; Tab to players column
	RET		; Return



Image of page 76 for reference





; **************************************************************
; TAB TO PLAYERS COLUMN
; **************************************************************
; FUNCTION:	--	To space over in the move listing to the
; 		column in which the players moves are being
; 		recorded. This routine also reprints the
; 		move number.
; 
; CALLED BY: -- PLYRMV
; 
; CALLS:	-- 	None
; 
; MACRO CALLS: 	PRTBLK
; 
; ARGUMENTS:	-- 	None
; 
; **************************************************************
TBPLCL:	PRTBLK	MVENUM,3 ;	Reproduce move number
	LDA	KOLOR ;	Computers color
	ANA	A ;	Is computer white ?
	RNZ ;		No - return
	PRTBLK	SPACE,6 ;	Tab to next column
	RET ; 		Return

; **************************************************************
TAB TO COMPUTERS COLUMN
; **************************************************************
; FUNCTION:	--	To space over in the move listing to the
; 		column in which the computers moves are
; 		being recorded. This routine also reprints
; 		the move number.
; 
; CALLED BY: --	DRIVER
; 	CPTRMV
; 
; CALLS:	-- 	None
; 
; MACRO CALLS: 	PRTBLK
; 
; ARGUMENTS:	-- 	None
; **************************************************************
TBCPCL:	PRTBLK	MVENUM,3 ;	Reproduce move number
	LDA	KOLOR ;	Computer's color
	ANA	A ;	Is computer white ?
	RZ ;		Yes - return
	PRTBLK	SPACE,6 ;	Tab to next column
	RET ; 		Return




Image of page 77 for reference





; **************************************************************
; TAB TO PLAYERS COLUMN W/0 MOVE NO.
; **************************************************************
; FUNCTION:	--	Like TBPLCL, except that the move number
; 		is not reprinted.
; 
; CALLED BY: -- FCDMAT
; ************************************************************
; TBPLMV:	PRTBLK	SPACE,3
; 	LDA	KOLOR
; 	ANA	A
; 	RNZ
; 	PRTBLK	SPACE,6
; 	RET
; 
; **************************************************************
TAB TO COMPUTERS COLUMN W/O MOVE NO.
; **************************************************************
; FUNCTION:	--	Like TBCPCL, except that the move number
; 		is not reprinted.
; 
;CALLED BY: -- CPTRMV
; **************************************************************
TBCPMV:	PRTBLK	SPACE,3
	LDA	KOLOR
	ANA	A
	RZ
	PRTBLK	SPACE,6
	RET




Image of page 78 for reference




; **************************************************************
; BOARD INDEX TO ASCII SQUARE NAME
; **************************************************************
; FUNCTION:	--	To translate a hexadecimal index in the
; 		board array into an ascii description
; 		of the square in algebraic chess notation.
; 
; CALLED BY: -- CPTRMV
; 
; CALLS:	-- 	DIVIDE
; 
; ARGUMENTS: --	Board index input in register D and the Ascii
; square name is output in register pair HL.
; **************************************************************
BITASN:	SUB	A	; Get ready for division
	MVI	E,10
	CALL	DIVIDE	; Divide
	DCR	D	; Get rank on 1-8 basis
	ADI	60H	; Convert file to Ascii (a-h)
	MOV	L,A	; Save
	MOV	A,D	; Rank
	ADI	30H	; Convert rank to Ascii (1-8)
	MOV	H,A	; Save
	RET		; Return




Image of page 79 for reference



; **************************************************************
; PLAYERS MOVE ANALYSIS
; **************************************************************
; FUNCTION:	--	To accept and validate the players move
; 		and produce it on the graphics board. Also
; 		allows player to resign the game by
; 		entering a control-R.
; 
; CALLED BY: -- DRIVER
; 
; CALLS:	--	CHARTR
; 		ASNTBI
; 		VALMOV
; 		EXECMV
; 		PGIFND
; 		TBPLCL
; 
; ARGUMENTS:	-- 	None
; **************************************************************
PLYRMV:	CALL	CHARTR	; Accept "from" file letter
	CPI	12H	; Is it instead a Control-R ?
	JZ	FM09	; Yes - jump
	MOV	H,A	; Save
	CALL	CHARTR	; Accept "from" rank number
	MOV	L,A	; Save
	CALL	ASNTBI	; Convert to a board index
	SUB	B	; Gives board index, if valid
	JRZ	PL08	; Jump if invalid
	STA	MVEMSG	; Move list "from" position
	CALL	CHARTR	; Accept separator & ignore it
	CALL	CHARTR	; Repeat for "to" position
	MOV	H,A
	CALL	CHARTR
	MOV	L,A
	CALL	ASNTBI
	SUB	B
	JRZ	PL08
	STA	MVEMSG+1	; Move list "to" position
	CALL	VALMOV	; Determines if a legal move
	ANA	A	; Legal ?
	JNZ	PL08	; No - jump
	CALL	EXECMV	; Make move on graphics board
	RET		; Return
PL08:	LXI	H,LINECT	; Address of screen line count
	INR	M	; Increase by 2 for message
	INR	M
	CARRET		; New line
	CALL	PGIFND	; New page if needed
	PRTLIN	INVAL1,12 ;	Output "INVALID MOVE"
	PRTLIN	INVAL2,9 ;	Output "TRY AGAIN"
	CALL	TBPLCL ;	Tab to players column
	JMP	PLYRMV ; 	Jump




Image of page 80 for reference




; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	ASCII SQUARE NAME TO BOARD INDEX
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	To convert an algebraic square name in
; 		Ascii to a hexadecimal board index.
; 		This routine also checks the input for
; 		validity.
; CALLED BY:	--	PLYRMV
; CALLS:	--	MLTPLY
; 
; ARGUMENTS: --	Accepts the square name in register pair HL and
; outputs the board index in register A. Register
; B = 0 if ok. Register B = Register A if invalid.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
ASNTBI:	MOV	A,L	; Ascii rank
	SUI	30H	; Rank 1 - 8
	CPI	1	; Check lower bound
	JM	AT04	; Jump if invalid
	CPI	9	; Check upper bound
	JRNC	AT04	; Jump if invalid
	INR	A .	; Rank 2 - 9
	MOV	D,A	; Ready for multiplication
	MVI	E,10
	CALL	MLTPLY	; Multiply
	MOV	A,H	; Ascii file letter (a - h)
	SUI	40H	; File 1 - 8
	CPI	1	; Check lower bound
	JM	AT04	; Jump if invalid
	CPI	9	; Check upper bound
	JRNC	AT04	; Jump if invalid
	ADD	D	; File+Rank(20-90)=Board index
	MVI	B,0	; Ok flag
	RET		; Return
AT04:	MOV	B,A	; Invalid flag
	RET		; Return




Image of page 81 for reference




; **********************************************************
; VALIDATE MOVE SUBROUTINE
; **********************************************************
; FUNCTION:	--	To check a players move for validity.
; 
; CALLED BY: -- PLYRMV
; 
; CALLS:	--	GENMOV
; 		MOVE
; 		INCHK
; 		UNMOVE
; 
; ARGUMENTS: --	Returns flag in register A, 0 for valid and 1 for
; invalid move.
; **********************************************************
VALMOV:	LHLD	MLPTRJ	; Save last move pointer
	PUSH	H	; Save register
	LDA	KOLOR	; Computers color
	XRI	80H	;Toggle color
	STA	COLOR	; Store
	LXI	H,PLYIX-2	; Load move list index
	SHLD	MLPTRI
	LXI	H,MLIST+1024	; Next available list pointer
	SHLD	MLNXT
	CALL	GENMOV	; Generate opponents moves
	LXI	X,MLIST+1024	; Index to start of moves
VA5:	LDA	MVEMSG	; "From" position
	CMP	MLFRP(X)	; Is it in list ?
	JRNZ	VA6	; No - jump
	LDA	MVEMSG+l	; "To" position
	CMP	MLTOP(X)	; Is it in list ?
	JRZ	VA7	; Yes - jump
VA6:	MOV	E,MLPTR(X)	; Pointer to next list move
	MOV	D,MLPTR+1 (X)
	XRA	A	; At end of list ?
	CMP	D
	JRZ	VA10	; Yes - jump
	PUSH	D	; Move to X register
	POP	X
	JMPR	VA5	; Jump
VA7:	SIXD	MLPTRJ	; Save opponents move pointer
	CALL	MOVE	; Make move on board array
	CALL	INCHK	; Was it a legal move ?
	ANA	A
	JRNZ	VA9	; No - jump
VA8:	POP	H	; Restore saved register
	RET		; Return
VA9:	CALL	UNMOVE	; Un-do move on board array
VA10:	MVI	A,l ;	Set flag for invalid move
	POP	H ;	Restore saved register
	SHLD	MLPTRJ ;	Save move pointer
	RET ; 		Return



Image of page 82 for reference




; **********************************************************
; ACCEPT INPUT CHARATER
; **********************************************************
; FUNCTION:	--	Accepts a single character input from the
; 		console keyboard and places it in the A
; 		register. The character is also echoed on
; 		the video screen, unless it is a carrage
; return, line feed, or backspace. Lower case
; alphabetic characters are folded to upper case.
; 
; CALLED BY: --	DRIVER
; 	INTERR
; 	PLYRMV
; 	ANALYS
; 
; CALLS:	-- 	None
; 
; ARGUMENTS:	--	Character input is output in register A.
; 
; 	NOTES:	--	This routine contains a reference to a
;   			monitor function of the Jove monitor, there-
; 			for the first few lines of this routine are
; 			system dependent.
; **********************************************************
CHARTR: RST	7	; Jove monitor single char inpt
	.BYTE 	81H,0
	CPI	ODH ;	Carriage return ?
	RZ ;		Yes - return
	CPI	OAH ;	Line feed ?
	RZ ;		Yes - return
	CPI	08H ;	Backspace ?
	RZ ;		Yes - return
	RST	7 ;	Jove monitor single char echo
	.BYTE 	81H,lAH
	ANI	7FH ;	Mask off parity bit
	CPI	7BH ;	Upper range check (z+l)
	RP ;		No need to fold - return
	CPI	61H ;	Lower-range check (a)
	RM ;		No need to fold - return
	SUI	20H ;	Change to one of A-Z
	RET ; 		Return




Image of page 83 for reference





; **********************************************************
; NEW PAGE IF NEEDED
; **********************************************************
; FUNCTION:	--	To clear move list output when the column
; 		has been filled.
; 
; CALLED BY: --	DRIVER
; 	PLYRMV
; 	CPTRMV
; 
; CALLS:	-- 	DSPBRD
; 
; ARGUMENTS: --	Returns a 1 in the A register if a new
; page was turned.
; xx**x*xx*xx**x***xx*xx********x**x***x*xx*x*x*xxxx*xx*xx
PGIFND:	LXI	H,LINECT	; Addr of page position counter
	INR	M	; Increment
	MVI	A,1BH	; Page bottom ?
	CMP	M
	RNC		; No - return
	CALL	DSPBRD	; Put up new page
	PRTLIN	TITLE4,15 ; Re-print titles
	PRTLIN	TITLE3,15
	MVI	A,1 ; Set line count back to 1
	STA	LINECT
	RET ; Return




Image of page 84 for reference



; **********************************************************
; DISPLAY MATED KING
; **********************************************************
; 	FUNCTION:	--	To tip over the computers King when
; 			mated.
; 
; CALLED BY: -- FCDMAT
; 
; CALLS:	--	CONVRT
; 		BLNKER
; 		INSPCE (Abnormal Call to IP04)
; 
; ARGUMENTS:	-- 	None
; **********************************************************
MATED:	LDA	KOLOR	; Computers color
	ANA	A	; Is computer white ?
	JRZ	.+9	; Yes - skip
	MVI	C,2	; Set black piece flag
	LDA	POSK+1	; Position of black King
	JMPR	MA08	; Jump
	MOV	C,A	; Clear black piece flag
	LDA	POSK	; Position of white King
MA08:	STA	BRDPOS	; Store King position
	STA	ANBDPS	; Again
	CALL	CONVRT	; Getting norm address in HL
	MVI	A,7	; Piece value of toppled King
	MVI	B,10	; Blink parameter
	CALL	BLNKER	; Blink King position
	LXI	Y,MAOC	; Prepare for abnormal call
	PUSH	Y
	PUSH	H
	PUSH	B
	PUSH	D
	PUSH	X
	PUSH	PSW
	JMP	IP04	; Call INSPCE
MAOC:	MVI	B,10	; Blink again
	LDA	ANBDPS
	STA	BRDPOS
	CALL	BLNKER
	RET		; Return




Image of page 85 for reference





; **********************************************************
; SET UP POSITION FOR ANALYSIS
; *********************************************************
; FUNCTION:	--	To enable user to set up any position
; 		for analysis, or to continue to play
; 		the game. The routine blinks the board
; 		squares in turn and the user has the option
; 		of leaving the contents unchanged by a
; 		carriage return, emptying the square by a 0,
; 		or inputting a piece of his chosing. To
; 		enter a piece, type in piece-code,color-code,
; 		moved-code.
; 
; 	Piece-code is a letter indicating the
; desired piece:
; 	K -	King
; 	Q -	Queen
; 	R -	Rook
; 	B -	Bishop
; 	N -	Knight
; 	P - 	Pawn
; 
; Color code is a letter, W for white, or B for
; black.
; 
; Moved-code is a number. 0 indicates the piece has never
; moved. 1 indicates the piece has moved.
; 
; A backspace will back up in the sequence of blinked
; squares. An Escape will terminate the blink cycle and
; verify that the position is correct, then procede
; with game initialization.
; 
; CALLED BY: -- DRIVER
; 
; CALLS:	--	CHARTR
; 		DPSBRD
; 		BLNKER
; 		ROYALT
; 		PLYRMV
; 		CPTRMV
; MACRO CALLS:		PRTLIN
; 		EXIT
; 		CLRSCR
; 		PRTBLK
; 		CARRET
; 
; ARGUMENTS:	-- 	None
; **********************************************************




Image of page 86 for reference





ANALYS: PRTLIN	ANAMSG,37	; "CARE TO ANALYSE A POSITION?"
	CALL	CHARTR ;	Accept answer
	CARRET ;		New line
	CPI	4EH ;	Is answer a "N" ?
	JRNZ	AN04 ;	No - jump
	EXIT ;		Return to monitor
AN04:	CALL	DSPBRD ;	Current board position
	MVI	A,21 ;	First board index
AN08:	STA	ANBDPS ;	Save
	STA	BRDPOS
	CALL	CONVRT ;	Norm address into HL register
	STA	M1 ;	Set up board index
	LIXD	M1
	MOV	A,BOARD(X) ;	Get board contents
	CPI	OFFH ;	Boarder square ?
	JRZ	AN19 ;	Yes - jump
	MVI	B,4H ;	Ready to blink square
	CALL	BLNKER ;	Blink
	CALL	CHARTR ;	Accept input
	CPI	1BH ;	Is it an escape ?
	JRZ	ANlB ;	Yes - jump
	CPI	08H ;	Is it a backspace ?
	JRZ	ANIA ;	Yes - jump
	CPI	ODH ;	Is it a carriage return ?
	JRZ	AN19 ;	Yes - jump
	LXI	B,7 ;	Number of types of pieces + 1
	LXI	H,PCS ;	Address of piece symbol table
	CCIR ;		Search
	JRNZ	AN18 ;	Jump if not found
	CALL	CHARTR ;	Accept and ignore separator
	CALL	CHARTR ;	Color of piece
	CPI	42H ;	Is it black ?
	JRNZ	.+4 ;	No - skip
	SET	7,C ;	Black piece indicator
	CALL	CHARTR ;	Accept and ignore separator
	CALL	CHARTR ;	Moved flag
	CPI	31H ;	Has piece moved ?
	JRNZ	AN18 ;	No - jump
	SET	3,C ;	Set moved indicator
AN18:	MOV	BOARD(X),C ;	Insert piece into board array
	CALL	DSPBRD ;	Update graphics board
AN19:	LDA	ANBDPS ;	Current board position
	INR	A ;	Next
	CPI	99 ;	Done ?
	JRNZ	AN08 ;	No - jump
	JMPR	AN04 ;	Jump
ANlA:	LDA	ANBDPS ;	Prepare to go back a square




Image of page 87 for reference



	SUI	3 ;	To get around boarder
	CPI	20 ;	Off the other end ?
	JNC	AN08 ;	No - jump
	MVI	A,98 ;	Wrap around to top of screen
ANOB:	JMP	AN08 ; 	Jump
ANlB:	PRTLIN	CRTNES,14	; Ask if correct
	CALL	CHARTR ;	Accept answer
	CPI	4EH ;	Is it "N" ?
	JZ	AN04 ;	No - jump
	CALL	ROYALT ;	Update positions of royalty
	CLRSCR ;		Blank screen
	CALL	INTERR ;	Accept color choice
ANlC:	PRTLIN	WSMOVE,17	; Ask whose move it is
	CALL	CHARTR	; Accept response
	CALL	DSPBRD	; Display graphics board
	PRTLIN	TITLE4,15	; Put up titles
	PRTLIN	TITLE3,15
	CPI	57H	; Is is whites move ?
	JZ	DRIV04	; Yes - jump
	PRTBLK	MvENUM,3	; Print move number
	PRTBLK	SPACE,6	; Tab to blacks column
	LDA	KOLOR	;	Computer's color
	ANA	A	;	Is computer white ?
	JRNZ	AN20	:	No - jump
	CALL	PLYRMV	;	Get players move
	CARRET		;	New line
	JMP	DROC	;	Jump
AN20:	CALL	CPTRMV	;	Get computers move
	CARRET		;	New line
	JMP	DROC	; 	Jump





Image of page 88 for reference





; **********************************************************
; UPDATE POSITIONS OF ROYALTY
; **********************************************************
; FUNCTION:	--	To update the positions of the Kings
; 		and Queen after a change of board position
; 		in ANALYS.
; 
; CALLED BY: -- ANALYS
; 
; CALLS:	-- 	None
; 
; ARGUMENTS:	-- 	None
; **********************************************************
ROYALT:	LXI	H,POSK	; Start of Royalty array
	MVI	B,4	; Clear all four positions
	MVI	M,0
	INX	H
	DJNZ	.-3
	MVI	A,21	; First board position
RY04:	STA	M1	; Set up board index
	LXI	H,POSK	; Address of King position
	LIXD	M1
	MOV	A,BOARD(X)	;Fetch board contents
	BIT	7,A	; Test color bit
	JRZ	.+3	; Jump if white
	INX	H	; Offset for black
	ANI	7	; Delete flags, leave piece
	CPI	KING	; King ?
	JRZ	RY08	; Yes - jump
	CPI	QUEEN	; Queen ?
	JRNZ	RYOC	; No - jump
	INX	H	; Queen position
	INX	H	; Plus offset
RY08:	LDA	M1	; Index
	MOV	M,A	; Save
RYOC:	LDA	M1	; Current position
	INR	A	; Next position
	CPI	99	; Done.?
	JRNZ	RY04	; No - jump
	RET		; Return




Image of page 89 for reference




; **********************************************************
; SET UP EMPTY BOARD
; **********************************************************
; FUNCTION:	--	Diplay graphics board and pieces.
; 
; CALLED BY: --	DRIVER
; 	ANALYS
; 	PGIFND
; 
; CALLS:		--	CONVRT
; 				INSPCE
; 	ARGUMENTS:	--		None
; NOTES:		--		This routine makes use of several fixed
; 				addresses in the video stoFage area of
; 				the Jupiter III computer, and is therefor
; 				system dependent. Each such reference will
; 				be marked.
; **********************************************************
	DSPBRD: PUSH		B		; Save registers
	PUSH		D
	PUSH		H
	PUSH	PSW
	CLRSCR		; Blank screen
	LXI	H,OC000H	; System Dependent-First video
				address
	MVI	M,80H	; Start of blank border
	LXI	D,0C001H	; Sys Dep- Next boarder square
	LXI	8,15	; Number of bytes to be moved
	LDIR		; Blank boarder bar
	MVI	M,OAAH	; First black boarder box
	INR	L	; Next block address
	MVI	B,6	; Number to be moved
DB04:	MVI	M,80H	; Create white block
	INR	L	; Next block address
	DJNZ	DB04	; Done ? No - jump
	MVI	B,6	; Number of repeats
DB08:	MVI	M,OBFH	; Create black box
	INR	L	; Next block address
	DJNZ	DB08	; Done ? No - jump
	XCHG		; Get ready for block move
	LXI	B,36	; Bytes to be moved
	LDIR		; Move - completes first bar
	LXI	H,0C000H	; S D - First addr to be copied
	LXI	B,ODOH	; Number of blocks to move
	LDIR		; Completes first rank
	LXI	H,OC016H	; S D - Start of copy area
	LXI	B,6	; Number of blocks to move




Image of page 90 for reference


	LDIR ;		First black square done
	LXI	H,OC010H ;	S D - Start copy area
	LXI	B,42 ;	Bytes to be moved
	LDIR ;		Rest of bar done
	LXI	H,OC100H ;	S D - Start of copy area
	LXI	B,OCOH ;	Move three bars
	LDIR ;		Next rank done
	LXI	H,OC000H ;	S D - Copy rest of screen
	LXI	B,600H ;	Number of blocks
	LDIR ;		Board done
BSETUP:	MVI	A,21 ;	First board index
BSET04:	STA	BRDPOS ;	Ready parameter
	CALL	CONVRT ;	Norm addr into HL regtisters
	CALL	INSPCE ;	Insert that piece onto board
	INR	A ;	Next square
	CPI	99 ;	Done ?
	JRC	BSET04 ;	No - jump
	POP	PSW ;	Restore registers
	POP	H
	POP	D
	POP	B
	RET




Image of page 91 for reference





; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; INSERT PIECE SUBROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	This subroutine places a piece onto a
; 		given square on the video board. The piece
; 		inserted is that stored in the board array
; 		for that square.
; CALLED BY:	--	DPSPRD
; 		MATED
; CALLS:	--	MLTPLY
; 
; ARGUMENTS: --	Norm address for the square in register pair HL.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
INSPCE:	PUSH	H	; Save registers
	PUSH	B
	PUSH	D
	PUSH	X
	PUSH	PSW
	LDA	BRDPOS	; Get board index
	STA	M1	; Save
	LIXD	M1	; Index into board array
	MOV	A,BOARD(X)	; Contents of board array
	ANA	A	; Is square empty ?
	JRZ	IP2C	; Yes - jump
	CPI	OFFH	; Is it a boarder square ?
	JRZ	IP2C	; Yes - jump
	MVI	C,0	; Clear flag register
	BIT	7,A	; Is piece white ?
	JRZ	IP04	; Yes - jump
	MVI	C,2	; Set black piece flag
IP04:	ANI	7	; Delete flags, leave piece
	DCR	A	; Piece on a 0 - 5 basis
	MOV	E,A	; Save
	MVI	D,16	; Multiplier
	CALL	MLTPLY	; For loc of piece in table
	M'OV	A,D	; Displacement into block table
	STA	INDXER	; Low order index byte
	LIXD	INDXER	; Get entire index
	BIT	O,M	; Is square white ?
	JRZ	IP08	; Yes - jump
	INR	C	; Set compliment flag
IP08:	INR	L	; Address of first alter block
	PUSH	H	; Save
	MVI	D,®	; Bar counter
IPOC:	MVI	B,4	; Block counter
IP10:	MOV	A,BLOCK(X)	; Bring in source block
	BIT	0,C	; Should it be complemented ?





Image of page 92 for reference



	JRZ	IP14	; No - jump
	XRI	3FH	; Graphics complement
IP14:	MOV	M,A	; Store block
	INR	L	; Next block
	INX	X	; Next source block
	DJNZ	"P10	; Done ? No - jump
	MOV	A,L	; Bar increment
	ADI	3CH
	MOV	L,A
	INR	D	; Bar counter
	BIT	2,D	; Done ?
	JRZ	IPOC	; No - jump
	POP	H	; Address of Norm + 1
	BIT	0,C	; Is square white ?
	JRNZ	IP18	; No - jump
	BIT	1,C	; Is piece white ?
	JRNZ	IP2C	; No - jump
	JMPR	IPIC	; Jump
IP18:	BIT	1,C	; Is piece white ?
	JRZ	IP2C	; Yes - jump
IPlC:	MVI	D,6	; Multiplier
	CALL	MLTPLY	; Multiply for displacement
	MOV	A,D	; Kernel table displacement
	STA	INDXER	; Save
	LIXD	INDXER	; Get complete index
	MOV	A,L	; Start of Kernel
	ADI	40H
	MOV	L,A
	MVI	D,0	; Bar counter
IP20:	MVI	B,3	; Block counter
IP24:	MOV	A,KERNEL(X)	; Kernel block
	BIT	1,C	; Need to complement ?
	JRNZ	IP28	; No - jump
	XRI	3FH	; Graphics complement
IP28:	MOV	M,A	; Store block
	INR	L	; Next target block
	INX	X	; Next source block
	DJNZ	IP24	; Done ? No - jump
	MOV	A,L	; Bar increment
	ADI	3DH
	MOV	L,A
	INR	D	; Bar counter
	BIT	1,D	; Done ?
	JRZ	IP20	; Repeat bar move
IP2C:	POP	PSW	; Restore registers
	POP	X
	POP	D
	POP	B
	POP	H
	RET



Image of page 93 for reference



; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; BOARD INDEX TO NORM ADDRESS SUBR.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 	FUNCTION:	--	Converts a hexadecimal board index into
; 			a Norm address for the square.
; 	CALLED BY:	--	DSPBRD
; 			INSPCE
; 			ANALYS
; 			MATED
; 	CALLS:	--	DIVIDE
; 			MLTPLY
;ARGUMENTS:	--	Returns the Norm address in register pair
; 			HL.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
CONVRT: PUSH	B	; Save registers
	PUSH	D
	PUSH	PSW
	LDA	BRDPOS	; Get board index
	MOV	D,A	; Set up dividend
	SUB	A
	MVI	E,10	; Divisor
	CALL	DIVIDE	; Index into rank and file
			; file (1-8) & rank (2-9)
	DCR	D	; For rank (1-8)
	DCR	A	; For file (0-7)
	MOV	C,D	; Save
	MVI	D,6	; Multiplier
	MOV	E,A	; File number is multiplicand
	CALL	MLTPLY	; Giving file displacement
	MOV	A,D	; Save
	ADI	10H	; File norm address
	MOV	L,A	; Low order address byte
	MVI	A,8	; Rank adjust
	SUB	C	; Rank displacement
	ADI	OCOH	; Rank Norm address
	MOV	H,A	; High order addres byte
	POP	PSW	; Restore registers
	POP	D
	POP	B
	RET		; Return




Image of page 94 for reference



; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; POSITIVE INTEGER DIVISION
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
DIVIDE:	PUSH	B
	MVI	B,8
DD04:	SLAR	D
	RAL
	SUB	E
	JM	.+6
	INR	D
	JMPR	.+3
	ADD	E
	DJNZ	DD04
	POP	B
	RET

; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; POSITIVE INTEGER MULTIPLICATION
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
MLTPLY:	PUSH	B
	SUB	A
	MVI	B,8
ML04:	BIT	0,D
	JRZ	.+3
	ADD	E
	SRAR	A
	RARR	D
	DJNZ	ML04
	POP	B
	RET




Image of page 95 for reference



; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; SQUARE BLINKER
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; 
; FUNCTION:	--	To blink the graphics board square to signal
; 		a piece's intention to move, or to high-
;	light the square as being alterable
; 			in ANALYS.
; 
; CALLED BY: --	MAKEMV
; 	ANALYS
; 	MATED
; 
; CALLS:	-- 	None
; 
; ARGUMENTS: --	Norm address of desired square passed in register
; pair HL. Number of times to blink passed in
; register B.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
BLNKER:	PUSH	PSW	; Save registers
	PUSH	B
	PUSH	D
	PUSH	H
	PUSH	X
	SHLD	NORMAD	; Save Norm address
BL04:	MVI	D,0	; Bar counter
BL08:	MVI	C,0	; Block counter
BLOC:	MOV	AIM	; Fetch block
	XRI	3FH	; Graphics complement
	MOV	M,A	; Replace block
	INR	L	; Next block address
	INR	C	; Increment block counter
	MOV	A,C
	CPI	6	; Done ?
	JRNZ	BLOC	; No - jump
	MOV	A,L	; Address
	ADI	3AH	; Adjust square position
	MOV	L,A	; Replace address
	INR	D	; Increment bar counter
	BIT	2,D	; Done ?
	JRZ	BL08	; No - jump
	LHLD	NORMAD	; Get Norm address
	PUSH	B	; Save register
	LXI	B,3030H	; Delay loop, for visibility
BL10:	DJNZ	BL10
	DCR	C
	JRNZ	BL10




Image of page 96 for reference



	POP	B ; Restore register
	DJNZ	BL04 ; Done ? No - jump
	POP	X ; Restore registers
	POP	H
	POP	D
	POP	B
	POP	PSW
	RET ; Return



Image of page 97 for reference



; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; EXECUTE MOVE SUBROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNCTION:	--	This routine is the control routine for
; 		MAKEMV. It checks for double moves and
; 		sees that they are properly handled. It
; 		sets flags in the B register for double
; 		moves:
; 			En Passant -- Bit 0
; 0-0	-- Bit 1
; 0-0-0	-- Bit 2
; 
; CALLED BY: --	PLYRMV
; 	CPTRMV
; 
; 	CALLS:	-- MAKEMV
; 
; 	ARGUMENTS:	-- Flags set in the B register as described
; above.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
EXECMV:	PUSH	X	; Save registers
	PUSH	PSW
	LIXD	MLPTRJ	; Index into move list
	MOV	C,MLPRP(X)	; Move list "from" position
	MOV	E,MLTOP(X)	; Move list "to" position
	CALL	MAKEMV	; Produce move
	MOV	D,MLFLG (X)	; Move list flags
	MVI	B,0
	BIT	6,D	; Double move ?
	JRZ	EX14	; No - jump
	LXI	D,6	; Move list entry width
	DADX	D	; Increment MLPTRJ
	MOV	C,MLFRP(X)	; Second "from" position
	MOV	E,MLTOP(X)	; Second "to" position
	MOV	A,E	; Get "to" position
	CMP	C	; Same as "from" position ?
	JRNZ	EX04	; No - jump
	INR	B	; Set en passant flag
	JMPR	EX10	; Jump
EX04:	CPI	1AH	; White 0-0 ?
	JRNZ	EX08	; No - jump
	SET	1,8	; Set 0-O flag
	JMPR	EX10	; Jump
EX08:	CPI	60H	; Black 0-0 ?
	JRNZ	EXOC	; No - jump
	SET	1,8	; Set 0-0 flag
	JMPR	8X10	; Jump
EXOC:	SET	2,B	; Set 0-0-0 flag
EX10:	CALL	MAkEMV	; Make 2nd move on board
EX14:	POP	PSW	; Restore registers
	POP	X
	RET		; Return





Image of page 98 for reference


; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; MAKE MOVE SUBROUTINE
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
; FUNDTION:	--	Moves the piece on the board when a move
; 		is made. It blinks both the "from" and
; 		"to" positions to give notice of the move.
; 
; CALLED BY: -- EXECMV
; 
; CALLS:	--	CONVRT
; 		BLNKER
; 		INSPCE
; 
; ARGUMENTS: --	The "from" position is passed in register C, and the
; "to" position in register E.
; xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
MAKEMV:	PUSH	PSW	; Save register
	PUSH	B
	PUSH	D
	PUSH	H
	MOV	A,C	; "From" position
	STA	BRDPOS	; Set up parameter
	CALL	CONVRT	; Getting Norm address in HL
	MVI	B,10	; Blink parameter
	CALL	BLNKER	; Blink "from" square
	MOV	A,M	; Bring in Norm 1plock
	INR	L	; First change block
	MVI	D,0	; Bar counter
MM04:	MVI	B,4	; Block counter
MM08:	MOV	M,A	; Insert blank block
	INR	L	; Next change block
	DJNZ	MM08	; Done ? No - jump
	MOV	C,A	; Saving norm block
	MOV	A,L	; Bar increment
	ADI	3CH
	MOV	L,A
	MOV	A,C	; Restore Norm block
	INR	D
	BIT	2,D	; Done ?
	JRZ	MM04	; No - jump
	MOV	A,E	; Get "to" position
	STA	BRDPOS	; Set up parameter
	CALL	CONVRT	; Getting Norm address in HL
	MVI	B,10	; Blink parameter
	CALL	INSPCE	; Inserts the piece
	CALL	BLNKER	; Blinks "to" square
	POP	H	; Restore registers
	POP	D
	POP	B
	POP	PSW
	RET		; Return

Image of page 99 for reference

TDL/ZILOG Mnemonics Conversion

 

symbols used

SYMBOL	OPERATION
r	one of the 8-bit registers A,B,C,D,E,H,L
n	any 8-bit absolute value
ii	an index register reference, either X or Y
d	an 8-bit index displacement, where -128< d< 127
zz	B for the BC register pair, D for the DE pair
nn	any 16-bit value, absolute or relocatable
rr	B for the BC register pair, D for the DE pair, H for the HL pair, SP for the stack pointer
qq	B for the BC register pair, D for the DE pair, H for the HL pair, PSW for the A/Flag pair
s	any of r (defined above), M, or d(ii)
IFF	interrupt flip-flop
CY	carry flip.-flop
ZF	zero flag
tt	B for the BC register pair, D for the DE pair, SP for the stack pointer, X for index register IX
uu	B for the BC register pair, D for the DE pair, SP for the stack pointer, Y for index register IY
b	a bit position in an 8-bit byte, where the bits are numbered from right to left 0 to 7
PC	program counter
b{n}	bit n of the 8-bit value or register v
vv/H	the most significant byte of the 16-bit value or register vv
vv/L	the least significant byte of the 16-bit value or register vv
Iv	an input operation on port v
Ov	an output operation on port v
w <- v	the value of w is replaced by the value of v
w <-> v	the value of w is exchanged with the value of v

Image of page 100 

Image of page 101 

Image of page 102 

Image of page 103 

Image of page 104 

Image of page 105 

Image of page 106 

Image of page 107 

Image of page 108 

Image of page 109 

Image of page 110 

Image of page 111 

---

 

INDEX TO SUBROUTINES

 

ADJPTR	33
ADMOVE	36
ANALYS	85
ASCEND	64
ASNTBI	80
ATKSAV	42
ATTACK	39
BITASN	76
BLNKER	94
BOOK	65
CASTLE	34
CHARTR	82
CONVRT	93
CPTRMV	73
DIVIDE	93
DRIVER	69
DSPBRD	89
ENPSNT	32
EVAL	60
EXECMV	97
FCDMAT	75
FNDMOV	59
GENMOV	38
INCHK	38
INITBD	27
INSPCE	91
INTERR	71
LIMIT	51
MAKEMV	98
MATED	84
MLTPLY	94
MOVE	54
MPIECE	30
NEXTAD	49
PATH	29
PGIFND	83
PINFND	44
PLYRMV	79
PNCK	43
POINTS	49
ROYALT	88
SORTM	58
TBCPCL	78
TBPLCL	76
TBPLMV	78
UNMOVE	56
vVALMOV	80
XCHNG	47