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microchess.c
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microchess.c
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//***********************************************************************
//
// Kim-1 MicroChess (c) 1976-2005 Peter Jennings, www.benlo.com
// 6502 emulation (c) 2005 Bill Forster
//
// Runs an emulation of the Kim-1 Microchess on any standard C platform
//
//***********************************************************************
// All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
// 3. The name of the author may not be used to endorse or promote products
// derived from this software without specific prior written permission.
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ''AS IS'' AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
// OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES// LOSS OF USE,
// DATA, OR PROFITS// OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//**********************************************************************
//*
//* Part 1
//* ------
//* Create virtual 6502 platform using standard C facilities.
//* Goal is to run Microchess on any platform supporting C.
//*
//* Part 1 added July 2005 by Bill Forster (www.triplehappy.com)
//**********************************************************************
// Standard library include files
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <setjmp.h>
#include <math.h>
// Use <setjmp.h> macros and functions to emulate the "jump to reset
// stack pointer then restart program" behaviour used by microchess
jmp_buf jmp_chess;
#define EXIT -1
#define RESTART -2
void RESTART_CHESS( void ) // start CHESS program with reset stack
{
longjmp( jmp_chess, RESTART );
}
void EXIT_TO_SYSTEM( void ) // return to operating system
{
longjmp( jmp_chess, EXIT );
}
// 6502 emulation memory
typedef unsigned char byte;
byte zeropage[256];
byte stack[256];
byte stack_cy[256];
byte stack_v[256];
// 6502 emulation registers
byte reg_a, reg_f, reg_x, reg_y, reg_s, reg_cy, reg_v, temp_cy;
unsigned int temp1, temp2;
// Debug stuff
#if 0
#define DBG , register_dump()
#else
#define DBG
#endif
void register_dump( void )
{
printf( "A=%02x X=%02x Y=%02x S=%02x F=%02X CY=%d V=%d\n",
reg_a, reg_x, reg_y, reg_s, reg_f, reg_cy, reg_v );
}
// 6502 emulation macros - register moves
#define T(src,dst) reg_f = (dst) = (src) DBG
#define A reg_a
#define S reg_s
#define X reg_x
#define Y reg_y
#define TYA T(Y,A)
#define TXS T(X,S)
#define TAX T(A,X)
#define TAY T(A,Y)
#define TSX T(S,X)
#define TXA T(X,A)
// 6502 emulation macros - branches
#define BEQ(label) if( reg_f == 0 ) goto label
#define BNE(label) if( reg_f != 0 ) goto label
#define BPL(label) if( ! (reg_f&0x80) ) goto label
#define BMI(label) if( reg_f & 0x80 ) goto label
#define BCC(label) if( !reg_cy ) goto label
#define BCS(label) if( reg_cy ) goto label
#define BVC(label) if( !reg_v ) goto label
#define BVS(label) if( reg_v ) goto label
#define BRA(label) /*extra*/ goto label
// 6502 emulation macros - call/return from functions
#define JSR(func) func()
#define RTS return
// 6502 emulation macros - jump to functions, note that in
// assembly language jumping to a function is a more efficient
// way of calling the function then returning, so we emulate
// that in the high level language by (actually) calling then
// returning. There is no JEQ 6502 opcode, but it's useful to
// us so we have made it up! (like BRA, SEV)
#define JMP(func) if( 1 ) { func(); return; } \
else // else eats ';'
#define JEQ(func) /*extra*/ if( reg_f == 0 ) { func(); return; } \
else // else eats ';'
// 6502 emulation macros - load registers
// Addressing conventions;
// default addressing mode is zero page, else indicate with suffix;
// i = immediate
// x = indexed, zero page
// f = indexed, not zero page (f for "far")
#define ZP(addr8) (zeropage[ (byte) (addr8) ])
#define ZPX(addr8,idx) (zeropage[ (byte) ((addr8)+(idx)) ])
#define LDAi(dat8) reg_f = reg_a = dat8 DBG
#define LDAx(addr8,idx) reg_f = reg_a = ZPX(addr8,idx) DBG
#define LDAf(addr16,idx) reg_f = reg_a = (addr16)[idx] DBG
#define LDA(addr8) reg_f = reg_a = ZP(addr8) DBG
#define LDXi(dat8) reg_f = reg_x = dat8 DBG
#define LDX(addr8) reg_f = reg_x = ZP(addr8) DBG
#define LDYi(dat8) reg_f = reg_y = dat8 DBG
#define LDY(addr8) reg_f = reg_y = ZP(addr8) DBG
#define LDYx(addr8,idx) reg_f = reg_y = ZPX(addr8,idx) DBG
// 6502 emulation macros - store registers
#define STA(addr8) ZP(addr8) = reg_a DBG
#define STAx(addr8,idx) ZPX(addr8,idx) = reg_a DBG
#define STX(addr8) ZP(addr8) = reg_x DBG
#define STY(addr8) ZP(addr8) = reg_y DBG
#define STYx(addr8,idx) ZPX(addr8,idx) = reg_y DBG
// 6502 emulation macros - set/clear flags
#define CLD // luckily CPU's BCD flag is cleared then never set
#define CLC reg_cy = 0 DBG
#define SEC reg_cy = 1 DBG
#define CLV reg_v = 0 DBG
#define SEV /*extra*/ reg_v = 1 /*avoid problematic V emulation*/ DBG
// 6502 emulation macros - accumulator logical operations
#define ANDi(dat8) reg_f = (reg_a &= dat8) DBG
#define ORA(addr8) reg_f = (reg_a |= ZP(addr8)) DBG
// 6502 emulation macros - shifts and rotates
#define ASL(addr8) reg_cy = (ZP(addr8)&0x80) ? 1 : 0, \
ZP(addr8) = ZP(addr8)<<1, \
reg_f = ZP(addr8) DBG
#define ROL(addr8) temp_cy = (ZP(addr8)&0x80) ? 1 : 0, \
ZP(addr8) = ZP(addr8)<<1, \
ZP(addr8) |= reg_cy, \
reg_cy = temp_cy, \
reg_f = ZP(addr8) DBG
#define LSR reg_cy = reg_a & 0x01, \
reg_a = reg_a>>1, \
reg_a &= 0x7f, \
reg_f = reg_a DBG
// 6502 emulation macros - push and pull
#define PHA stack[reg_s--] = reg_a DBG
#define PLA reg_a = stack[++reg_s] DBG
#define PHY stack[reg_s--] = reg_y DBG
#define PLY reg_y = stack[++reg_s] DBG
#define PHP stack [reg_s] = reg_f, \
stack_cy[reg_s] = reg_cy, \
stack_v [reg_s] = reg_v, \
reg_s-- DBG
#define PLP reg_s++, \
reg_f = stack [reg_s], \
reg_cy = stack_cy[reg_s], \
reg_v = stack_v [reg_s] DBG
// 6502 emulation macros - compare
#define cmp(reg,dat) reg_f = ((reg) - (dat)), \
reg_cy = ((reg) >= (dat) ? 1 : 0) DBG
#define CMPi(dat8) cmp( reg_a, dat8 )
#define CMP(addr8) cmp( reg_a, ZP(addr8) )
#define CMPx(addr8,idx) cmp( reg_a, ZPX(addr8,idx) )
#define CMPf(addr16,idx) cmp( reg_a, (addr16)[idx] )
#define CPXi(dat8) cmp( reg_x, dat8 )
#define CPXf(addr16,idx) cmp( reg_x, (addr16)[idx] )
#define CPYi(dat8) cmp( reg_y, dat8 )
// 6502 emulation macros - increment,decrement
#define DEX reg_f = --reg_x DBG
#define DEY reg_f = --reg_y DBG
#define DEC(addr8) reg_f = --ZP(addr8) DBG
#define INX reg_f = ++reg_x DBG
#define INY reg_f = ++reg_y DBG
#define INC(addr8) reg_f = ++ZP(addr8) DBG
#define INCx(addr8,idx) reg_f = ++ZPX(addr8,idx) DBG
// 6502 emulation macros - add
#define adc(dat) temp1 = reg_a, \
temp2 = (dat), \
temp1 += (temp2+(reg_cy?1:0)), \
reg_f = reg_a = (byte)temp1, \
reg_cy = ((temp1&0xff00)?1:0) DBG
#define ADCi(dat8) adc( dat8 )
#define ADC(addr8) adc( ZP(addr8) )
#define ADCx(addr8,idx) adc( ZPX(addr8,idx) )
#define ADCf(addr16,idx) adc( (addr16)[idx] )
// 6502 emulation macros - subtract
// (note that both as an input and an output cy flag has opposite
// sense to that used for adc(), seems unintuitive to me)
#define sbc(dat) temp1 = reg_a, \
temp2 = (dat), \
temp1 -= (temp2+(reg_cy?0:1)), \
reg_f = reg_a = (byte)temp1, \
reg_cy = ((temp1&0xff00)?0:1) DBG
#define SBC(addr8) sbc( ZP(addr8) )
#define SBCx(addr8,idx) sbc( ZPX(addr8,idx) )
// Test some of the trickier opcodes (hook this up as needed)
void test_function( void )
{
byte hi, lo;
LDAi (0x33); // 0x4444 - 0x3333 = 0x1111
STA (0);
STA (1);
LDAi (0x44);
SEC;
SBC (0);
lo = reg_a;
LDAi (0x44);
SBC (1);
hi = reg_a;
LDAi (0x44); // 0x3333 - 0x4444 = 0xeeef
STA (0);
STA (1);
LDAi (0x33);
SEC;
SBC (0);
lo = reg_a;
LDAi (0x33);
SBC (1);
hi = reg_a;
LDAi (0x33); // 0x3333 + 0x4444 = 0x7777
STA (0);
STA (1);
LDAi (0x44);
CLC;
ADC (0);
lo = reg_a;
LDAi (0x44);
ADC (1);
hi = reg_a;
}
//**********************************************************************
//*
//* Part 2
//* ------
//* Original microchess program by Peter Jennings, www.benlo.com
//* In this form, 6502 assembly language has been minimally transformed
//* to run with the virtual 6502 in C facilities created in part 1.
//* (New comments by Bill Forster are identified with text (WRF))
//**********************************************************************
//
// page zero variables
//
const byte BOARD = 0x50;
const byte BK = 0x60;
const byte PIECE = 0xB0;
const byte SQUARE = 0xB1;
const byte SP2 = 0xB2;
const byte SP1 = 0xB3;
const byte INCHEK = 0xB4;
const byte STATE = 0xB5;
const byte MOVEN = 0xB6;
const byte REV = 0xB7;
const byte OMOVE = 0xDC;
const byte WCAP0 = 0xDD;
const byte COUNT = 0xDE;
const byte BCAP2 = 0xDE;
const byte WCAP2 = 0xDF;
const byte BCAP1 = 0xE0;
const byte WCAP1 = 0xE1;
const byte BCAP0 = 0xE2;
const byte MOB = 0xE3;
const byte MAXC = 0xE4;
const byte CC = 0xE5;
const byte PCAP = 0xE6;
const byte BMOB = 0xE3;
const byte BMAXC = 0xE4;
const byte BMCC = 0xE5; // was BCC (TASS doesn't like it as a label)
const byte BMAXP = 0xE6;
const byte XMAXC = 0xE8;
const byte WMOB = 0xEB;
const byte WMAXC = 0xEC;
const byte WCC = 0xED;
const byte WMAXP = 0xEE;
const byte PMOB = 0xEF;
const byte PMAXC = 0xF0;
const byte PCC = 0xF1;
const byte PCP = 0xF2;
const byte OLDKY = 0xF3;
const byte BESTP = 0xFB;
const byte BESTV = 0xFA;
const byte BESTM = 0xF9;
const byte DIS1 = 0xFB;
const byte DIS2 = 0xFA;
const byte DIS3 = 0xF9;
const byte temp = 0xFC;
// (WRF) For C version, data definitions precede code references to data
byte SETW[] = { 0x03, 0x04, 0x00, 0x07, 0x02, 0x05, 0x01, 0x06,
0x10, 0x17, 0x11, 0x16, 0x12, 0x15, 0x14, 0x13,
0x73, 0x74, 0x70, 0x77, 0x72, 0x75, 0x71, 0x76,
0x60, 0x67, 0x61, 0x66, 0x62, 0x65, 0x64, 0x63
};
byte MOVEX[] = { 0x00, 0xF0, 0xFF, 0x01, 0x10, 0x11, 0x0F, 0xEF, 0xF1,
0xDF, 0xE1, 0xEE, 0xF2, 0x12, 0x0E, 0x1F, 0x21
};
byte POINTS[] = { 0x0B, 0x0A, 0x06, 0x06, 0x04, 0x04, 0x04, 0x04,
0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02
};
byte OPNING[] = { 0x99, 0x25, 0x0B, 0x25, 0x01, 0x00, 0x33, 0x25,
0x07, 0x36, 0x34, 0x0D, 0x34, 0x34, 0x0E, 0x52,
0x25, 0x0D, 0x45, 0x35, 0x04, 0x55, 0x22, 0x06,
0x43, 0x33, 0x0F, 0xCC
};
// (WRF) level information:
// | Level | addr=02F2 | addr=018B
// | | (level1) | (level2)
// +-------------+-----------+-------------
// | SUPER BLITZ | 00 | FF
// | BLITZ | 00 | FB
// | NORMAL | 08 | FB
static byte level1=8;
static byte level2=0xfb;
// (WRF) Forward declarations
void CHESS( void );
void JANUS( void );
void INPUT( void );
void DISP( void );
void GNMZ( void );
void GNMX( void );
void GNM( void );
void RUM( void );
void STRV( void );
void SNGMV( void );
void LINE( void );
void REVERSE( void );
void CMOVE( void );
void RESET( void );
void GENRM( void );
void UMOVE( void );
void MOVE( void );
void CKMATE( void );
void GO( void );
void DISMV( void );
void STRATGY( void );
void POUT( void );
void POUT5(void );
void POUT8(void );
void POUT9( void );
void POUT10( void );
void POUT12( void );
void POUT13( void );
void KIN( void );
void syskin( void );
void syschout( void );
void syshexout( void );
void PrintDig( void );
// WRF debug stuff
static void show_move_evaluation( int ivalue );
static void show_move_generation( byte src, byte dst );
static int bool_show_move_evaluation;
static int bool_show_move_generation;
// Start here; Was *=$1000 ; load into RAM @ $1000-$15FF
int main( int argc, char* argv[] )
{
LDAi (0x00); // REVERSE TOGGLE
STA (REV);
// JSR (Init_6551);
if( EXIT != setjmp(jmp_chess) )
CHESS(); // after setjmp() and then any
// subsequent RESTART_CHESS()
return(0); // after EXIT_TO_SYSTEM()
}
void CHESS( void )
{
CHESS_BEGIN: //
CLD; // INITIALIZE
LDXi (0xFF); // TWO STACKS
TXS;
LDXi (0xC8);
STX (SP2);
//
// ROUTINES TO LIGHT LED
// DISPLAY AND GET KEY
// FROM KEYBOARD
//
/*OUT:*/ JSR (POUT); // DISPLAY AND
JSR (KIN); // GET INPUT *** my routine waits for a keypress
// CMP (OLDKY); // KEY IN ACC *** no need to debounce
// BEQ (OUT); // (DEBOUNCE)
// STA (OLDKY);
//
CMPi (0x43); // [C]
BNE (NOSET); // SET UP
LDXi (0x1F); // BOARD
WHSET: LDAf (SETW,X); // FROM
STAx (BOARD,X); // SETW
DEX;
BPL (WHSET);
LDXi (0x1B); // *ADDED
STX (OMOVE); // INITS TO 0xFF
LDAi (0xCC); // Display CCC
BNE (CLDSP);
//
NOSET: CMPi (0x45); // [E]
BNE (NOREV); // REVERSE
JSR (REVERSE); // BOARD IS
SEC;
LDAi (0x01);
SBC (REV);
STA (REV); // TOGGLE REV FLAG
LDAi (0xEE); // IS
BNE (CLDSP);
//
NOREV: CMPi (0x40); // [P]
BNE (NOGO); // PLAY CHESS
JSR (GO);
CLDSP: STA (DIS1); // DISPLAY
STA (DIS2); // ACROSS
STA (DIS3); // DISPLAY
BNE (CHESS_BEGIN);
//
NOGO: CMPi (0x0D); // [Enter]
BNE (NOMV); // MOVE MAN
JSR (MOVE); // AS ENTERED
JMP (DISP); //
NOMV: CMPi (0x41); // [Q] ***Added to allow game exit***
BEQ (DONE); // quit the game, exit back to system.
JMP (INPUT); //
DONE: JMP (EXIT_TO_SYSTEM); // JMP (0xFF00); // *** MUST set this to YOUR OS starting address
}
//
// THE ROUTINE JANUS DIRECTS THE
// ANALYSIS BY DETERMINING WHAT
// SHOULD OCCUR AFTER EACH MOVE
// GENERATED BY GNM
//
//
//
void JANUS( void )
{ LDX (STATE);
BMI (NOCOUNT);
//
// THIS ROUTINE COUNTS OCCURRENCES
// IT DEPENDS UPON STATE TO INDEX
// THE CORRECT COUNTERS
//
/*COUNTS:*/ LDA (PIECE);
BEQ (OVER); // IF STATE=8
CPXi (0x08); // DO NOT COUNT
BNE (OVER); // BLK MAX CAP
CMP (BMAXP); // MOVES FOR
BEQ (XRT); // WHITE
//
OVER: INCx (MOB,X); // MOBILITY
CMPi (0x01); // + QUEEN
BNE (NOQ); // FOR TWO
INCx (MOB,X);
//
NOQ: BVC (NOCAP);
LDYi (0x0F); // CALCULATE
LDA (SQUARE); // POINTS
ELOOP: CMPx (BK,Y); // CAPTURED
BEQ (FOUN); // BY THIS
DEY; // MOVE
BPL (ELOOP);
FOUN: LDAf (POINTS,Y);
CMPx (MAXC,X);
BCC (LESS); // SAVE IF
STYx (PCAP,X); // BEST THIS
STAx (MAXC,X); // STATE
//
LESS: CLC;
PHP; // ADD TO
ADCx (CC,X); // CAPTURE
STAx (CC,X); // COUNTS
PLP;
//
NOCAP: CPXi (0x04);
BEQ (ON4);
BMI (TREE); //(=00 ONLY)
XRT: RTS;
//
// GENERATE FURTHER MOVES FOR COUNT
// AND ANALYSIS
//
ON4: LDA (XMAXC); // SAVE ACTUAL
STA (WCAP0); // CAPTURE
LDAi (0x00); // STATE=0
STA (STATE);
JSR (MOVE); // GENERATE
JSR (REVERSE); // IMMEDIATE
JSR (GNMZ); // REPLY MOVES
JSR (REVERSE);
//
LDAi (0x08); // STATE=8
STA (STATE); // GENERATE
JSR (GNM); // CONTINUATION
JSR (UMOVE); // MOVES
//
JMP (STRATGY); //
NOCOUNT: CPXi (0xF9);
BNE (TREE);
//
// DETERMINE IF THE KING CAN BE
// TAKEN, USED BY CHKCHK
//
LDA (BK); // IS KING
CMP (SQUARE); // IN CHECK?
BNE (RETJ); // SET INCHEK=0
LDAi (0x00); // IF IT IS
STA (INCHEK);
RETJ: RTS;
//
// IF A PIECE HAS BEEN CAPTURED BY
// A TRIAL MOVE, GENERATE REPLIES &
// EVALUATE THE EXCHANGE GAIN/LOSS
//
TREE: BVC (RETJ); // NO CAP
LDYi (0x07); // (PIECES)
LDA (SQUARE);
LOOPX: CMPx (BK,Y);
BEQ (FOUNX);
DEY;
BEQ (RETJ); // (KING)
BPL (LOOPX); // SAVE
FOUNX: LDAf (POINTS,Y); // BEST CAP
CMPx (BCAP0,X); // AT THIS
BCC (NOMAX); // LEVEL
STAx (BCAP0,X);
NOMAX: DEC (STATE);
LDAf (&level2,0); // IF STATE=FB (WRF, was LDAi (0xFB);)
CMP (STATE); // TIME TO TURN
BEQ (UPTREE); // AROUND
JSR (GENRM); // GENERATE FURTHER
UPTREE: INC (STATE); // CAPTURES
RTS;
}
//
// THE PLAYER'S MOVE IS INPUT
//
void INPUT( void )
{
CMPi (0x08); // NOT A LEGAL
BCS (ERROR); // SQUARE #
JSR (DISMV);
JMP (DISP); // fall through
ERROR: JMP (RESTART_CHESS);
}
void DISP( void )
{
LDXi (0x1F);
SEARCH: LDAx (BOARD,X);
CMP (DIS2);
BEQ (HERE); // DISPLAY
DEX; // PIECE AT
BPL (SEARCH); // FROM
HERE: STX (DIS1); // SQUARE
STX (PIECE);
JMP (RESTART_CHESS);
}
//
// GENERATE ALL MOVES FOR ONE
// SIDE, CALL JANUS AFTER EACH
// ONE FOR NEXT STEP
//
//
void GNMZ( void )
{
LDXi (0x10); // CLEAR
JMP (GNMX); // fall through
}
void GNMX( void )
{
LDAi (0x00); // COUNTERS
CLEAR: STAx (COUNT,X);
DEX;
BPL (CLEAR);
JMP (GNM); // fall though
}
void GNM( void )
{
LDAi (0x10); // SET UP
STA (PIECE); // PIECE
NEWP: DEC (PIECE); // NEW PIECE
BPL (NEX); // ALL DONE?
RTS; // -YES
//
NEX: JSR (RESET); // READY
LDY (PIECE); // GET PIECE
LDXi (0x08);
STX (MOVEN); // COMMON START
CPYi (0x08); // WHAT IS IT?
BPL (PAWN); // PAWN
CPYi (0x06);
BPL (KNIGHT); // KNIGHT
CPYi (0x04);
BPL (BISHOP); // BISHOP
CPYi (0x01);
BEQ (QUEEN); // QUEEN
BPL (ROOK); // ROOK
//
KING: JSR (SNGMV); // MUST BE KING!
BNE (KING); // MOVES
BEQ (NEWP); // 8 TO 1
QUEEN: JSR (LINE);
BNE (QUEEN); // MOVES
BEQ (NEWP); // 8 TO 1
//
ROOK: LDXi (0x04);
STX (MOVEN); // MOVES
AGNR: JSR (LINE); // 4 TO 1
BNE (AGNR);
BEQ (NEWP);
//
BISHOP: JSR (LINE);
LDA (MOVEN); // MOVES
CMPi (0x04); // 8 TO 5
BNE (BISHOP);
BEQ (NEWP);
//
KNIGHT: LDXi (0x10);
STX (MOVEN); // MOVES
AGNN: JSR (SNGMV); // 16 TO 9
LDA (MOVEN);
CMPi (0x08);
BNE (AGNN);
BEQ (NEWP);
//
PAWN: LDXi (0x06);
STX (MOVEN);
P1: JSR (CMOVE); // RIGHT CAP?
BVC (P2);
BMI (P2);
JSR (JANUS); // YES
P2: JSR (RESET);
DEC (MOVEN); // LEFT CAP?
LDA (MOVEN);
CMPi (0x05);
BEQ (P1);
P3: JSR (CMOVE); // AHEAD
BVS (NEWP); // ILLEGAL
BMI (NEWP);
JSR (JANUS);
LDA (SQUARE); // GETS TO
ANDi (0xF0); // 3RD RANK?
CMPi (0x20);
BEQ (P3); // DO DOUBLE
BRA (NEWP); // JMP (NEWP);
}
//
// CALCULATE SINGLE STEP MOVES
// FOR K,N
//
void SNGMV( void )
{
JSR (CMOVE); // CALC MOVE
BMI (ILL1); // -IF LEGAL
JSR (JANUS); // -EVALUATE
ILL1: JSR (RESET);
DEC (MOVEN);
RTS;
}
//
// CALCULATE ALL MOVES DOWN A
// STRAIGHT LINE FOR Q,B,R
//
void LINE( void )
{
LINE: JSR (CMOVE); // CALC MOVE
BCC (OVL); // NO CHK
BVC (LINE); // NOCAP
OVL: BMI (ILL); // RETURN
PHP;
JSR (JANUS); // EVALUATE POSN
PLP;
BVC (LINE); // NOT A CAP
ILL: JSR (RESET); // LINE STOPPED
DEC (MOVEN); // NEXT DIR
RTS;
}
//
// EXCHANGE SIDES FOR REPLY
// ANALYSIS
//
void REVERSE( void )
{
LDXi (0x0F);
ETC: SEC;
LDYx (BK,X); // SUBTRACT
LDAi (0x77); // POSITION
SBCx (BOARD,X); // FROM 77
STAx (BK,X);
STYx (BOARD,X); // AND
SEC;
LDAi (0x77); // EXCHANGE
SBCx (BOARD,X); // PIECES
STAx (BOARD,X);
DEX;
BPL (ETC);
RTS;
}
//
// CMOVE CALCULATES THE TO SQUARE
// USING SQUARE AND THE MOVE
// TABLE FLAGS SET AS FOLLOWS:
// N - ILLEGAL MOVE
// V - CAPTURE (LEGAL UNLESS IN CH)
// C - ILLEGAL BECAUSE OF CHECK
// [MY THANKS TO JIM BUTTERFIELD
// WHO WROTE THIS MORE EFFICIENT
// VERSION OF CMOVE]
//
void CMOVE( void )
{
byte src;
LDA (SQUARE); // GET SQUARE
src = reg_a;
LDX (MOVEN); // MOVE POINTER
CLC;
ADCf (MOVEX,X); // MOVE LIST
STA (SQUARE); // NEW POS'N
ANDi (0x88);
BNE (ILLEGAL); // OFF BOARD
LDA (SQUARE);
if( bool_show_move_generation )
show_move_generation( src, reg_a );
//
LDXi (0x20);
LOOP: DEX; // IS TO
BMI (NO); // SQUARE
CMPx (BOARD,X); // OCCUPIED?
BNE (LOOP);
//
CPXi (0x10); // BY SELF?
BMI (ILLEGAL);
//
// LDAi (0x7F); // MUST BE CAP!
// ADCi (0x01); // SET V FLAG
SEV; LDAi(0x80); // Avoid problematic V emulation
BVS (SPX); // (JMP)
//
NO: CLV; // NO CAPTURE
//
SPX: LDA (STATE); // SHOULD WE
BMI (RETL); // DO THE
CMPf (&level1,0); // CHECK CHECK? (WRF: was CMPi (0x08);)
BPL (RETL);
//
// CHKCHK REVERSES SIDES
// AND LOOKS FOR A KING
// CAPTURE TO INDICATE
// ILLEGAL MOVE BECAUSE OF
// CHECK SINCE THIS IS
// TIME CONSUMING, IT IS NOT
// ALWAYS DONE
//
/*CHKCHK:*/ PHA; // STATE
PHP;
LDAi (0xF9);
STA (STATE); // GENERATE
STA (INCHEK); // ALL REPLY
JSR (MOVE); // MOVES TO
JSR (REVERSE); // SEE IF KING
JSR (GNM); // IS IN
JSR (RUM); // CHECK
PLP;
PLA;
STA (STATE);
LDA (INCHEK);
BMI (RETL); // NO - SAFE
SEC; // YES - IN CHK
LDAi (0xFF);
RTS;
//
RETL: CLC; // LEGAL
LDAi (0x00); // RETURN
RTS;
//
ILLEGAL: LDAi (0xFF);
CLC; // ILLEGAL
CLV; // RETURN
RTS;
}
//
// REPLACE PIECE ON CORRECT SQUARE
//
void RESET( void )
{
LDX (PIECE); // GET LOGAT
LDAx (BOARD,X); // FOR PIECE
STA (SQUARE); // FROM BOARD
RTS;
}
//
//
//
void GENRM( void )
{
JSR (MOVE); // MAKE MOVE
/*GENR2:*/ JSR (REVERSE); // REVERSE BOARD
JSR (GNM); // GENERATE MOVES
JMP (RUM); // fall through
}
void RUM( void )
{
JSR (REVERSE); // REVERSE BACK
JMP (UMOVE); // fall through
}
//
// ROUTINE TO UNMAKE A MOVE MADE BY
// MOVE
//
void UMOVE( void )
{
TSX; // UNMAKE MOVE
STX (SP1);
LDX (SP2); // EXCHANGE
TXS; // STACKS
PLA; // MOVEN
STA (MOVEN);
PLA; // CAPTURED
STA (PIECE); // PIECE
TAX;
PLA; // FROM SQUARE
STAx (BOARD,X);
PLA; // PIECE
TAX;
PLA; // TO SOUARE
STA (SQUARE);
STAx (BOARD,X);
JMP (STRV);
}
//
// THIS ROUTINE MOVES PIECE
// TO SQUARE, PARAMETERS
// ARE SAVED IN A STACK TO UNMAKE
// THE MOVE LATER
//
void MOVE( void )
{ TSX;
STX (SP1); // SWITCH
LDX (SP2); // STACKS
TXS;
LDA (SQUARE);
PHA; // TO SQUARE
TAY;
LDXi (0x1F);
CHECK: CMPx (BOARD,X); // CHECK FOR
BEQ (TAKE); // CAPTURE
DEX;
BPL (CHECK);
TAKE: LDAi (0xCC);
STAx (BOARD,X);
TXA; // CAPTURED
PHA; // PIECE
LDX (PIECE);
LDAx (BOARD,X);
STYx (BOARD,X); // FROM
PHA; // SQUARE
TXA;
PHA; // PIECE
LDA (MOVEN);
PHA; // MOVEN
JMP (STRV); // fall through
}
// (WRF) Fortunately when we swap stacks we jump here and swap back before
// returning. So we aren't swapping stacks to do threading (if we were we
// would need to enhance 6502 stack emulation to incorporate our
// subroutine mechanism, instead we simply use the native C stack for
// subroutine return addresses).
void STRV( void )
{
TSX;
STX (SP2); // SWITCH
LDX (SP1); // STACKS
TXS; // BACK
RTS;
}
//
// CONTINUATION OF SUB STRATGY
// -CHECKS FOR CHECK OR CHECKMATE
// AND ASSIGNS VALUE TO MOVE
//
void CKMATE( void )
{
LDX (BMAXC); // CAN BLK CAP
CPXf (POINTS,0); // MY KING?
BNE (NOCHEK);
LDAi (0x00); // GULP!
BEQ (RETV); // DUMB MOVE!
//
NOCHEK: LDX (BMOB); // IS BLACK
BNE (RETV); // UNABLE TO
LDX (WMAXP); // MOVE AND
BNE (RETV); // KING IN CH?
LDAi (0xFF); // YES! MATE
//
RETV: LDXi (0x04); // RESTORE
STX (STATE); // STATE=4
//
// THE VALUE OF THE MOVE (IN ACCU)
// IS COMPARED TO THE BEST MOVE AND
// REPLACES IT IF IT IS BETTER
//
if( bool_show_move_evaluation )
show_move_evaluation( reg_a );
/*PUSH:*/ CMP (BESTV); // IS THIS BEST
BCC (RETP); // MOVE SO FAR?
BEQ (RETP);
if( bool_show_move_evaluation )
printf( "NEW BEST MOVE\n" );
STA (BESTV); // YES!
LDA (PIECE); // SAVE IT
STA (BESTP);
LDA (SQUARE);
STA (BESTM); // FLASH DISPLAY
RETP: LDAi ('.'); // print ... instead of flashing disp
JMP (syschout); // print . and return
}
//
// MAIN PROGRAM TO PLAY CHESS
// PLAY FROM OPENING OR THINK
//
void GO( void )
{
LDX (OMOVE); // OPENING?
BMI (NOOPEN); // -NO *ADD CHANGE FROM BPL
LDA (DIS3); // -YES WAS
CMPf (OPNING,X); // OPPONENT'S
BNE (END); // MOVE OK?
DEX;
LDAf (OPNING,X); // GET NEXT
STA (DIS1); // CANNED
DEX; // OPENING MOVE
LDAf (OPNING,X);
STA (DIS3); // DISPLAY IT
DEX;