e6502/opcodes.c

#include <stdint.h>
#include <stdio.h>

#include "opcodes.h"


#define adr_imp (NULL)

static int adr_imm(const uint8_t* operand, char* str, int max) {
    return snprintf(str, max, "#$%02X", *operand);
}

static int adr_acc(const uint8_t* operand, char* str, int max) {
    return snprintf(str, max, "A");
}

static int adr_ind(const uint8_t* operand, char* str, int max) {
    return snprintf(str, max, "($%04X)", *(uint16_t*)operand);
}

static int adr_abs(const uint8_t* operand, char* str, int max) {
    return snprintf(str, max, "$%04X", *(uint16_t*)operand);
}

static inline int adr_abs_reg(char reg, const uint8_t* op,
                              char* str, int max) {
    return snprintf(str, max, "$%04X,%c", *(uint16_t*)op, reg);
}

static int adr_abs_x(const uint8_t* operand, char* str, int max) {
    return adr_abs_reg('X', operand, str, max);
}

static int adr_abs_y(const uint8_t* operand, char* str, int max) {
    return adr_abs_reg('Y', operand, str, max);
}

#define adr_rel adr_zp
static int adr_zp(const uint8_t* operand, char* str, int max) {
    return snprintf(str, max, "$%02X", *operand);
}

static inline int adr_zp_reg(char reg, const uint8_t* operand,
                             char* str, int max) {
    return snprintf(str, max, "$%02X,%c", *operand, reg);
}

static int adr_zp_x(const uint8_t* operand, char* str, int max) {
    return adr_zp_reg('X', operand, str, max);
}

static int adr_zp_y(const uint8_t* operand, char* str, int max) {
    return adr_zp_reg('Y', operand, str, max);
}

static inline int adr_ind_reg(char reg, const uint8_t* op,
                              char* str, int max) {
    return snprintf(str, max, "($%04X,%c)", *(uint16_t*)op, reg);
}

static int adr_ind_x(const uint8_t* operand, char* str, int max) {
    return adr_ind_reg('X', operand, str, max);
}

static int adr_ind_y(const uint8_t* operand, char* str, int max) {
    return adr_ind_reg('Y', operand, str, max);
}

typedef int(*adr_Mode)(const uint8_t*, char*, int);

typedef struct {
    const char *operator;
    int(*mode)(const uint8_t*, char*, int);
    int cycles; // Unused
} e6502_Instruction;

#define brk "BRK"
#define ora "ORA"
#define asl "ASL"
#define asl_a asl
#define php "PHP"
#define bpl "BPL"
#define clc "CLC"
#define jsr "JSR"
#define bit "BIT"
#define and "AND"
#define rol "ROL"
#define rol_a rol
#define plp "PLP"
#define bmi "BMI"
#define sec "SEC"
#define rti "RTI"
#define eor "EOR"
#define lsr "LSR"
#define lsr_a lsr
#define pha "PHA"
#define jmp "JMP"
#define bvc "BVC"
#define cli "CLI"
#define rts "RTS"
#define adc "ADC"
#define ror "ROR"
#define ror_a ror
#define pla "PLA"
#define bvs "BVS"
#define sei "SEI"
#define sta "STA"
#define stx "STX"
#define sty "STY"
#define txa "TXA"
#define dey "DEY"
#define bcc "BCC"
#define tya "TYA"
#define txs "TXS"
#define lda "LDA"
#define ldx "LDX"
#define ldy "LDY"
#define tax "TAX"
#define tay "TAY"
#define bcs "BCS"
#define clv "CLV"
#define tsx "TSX"
#define cpy "CPY"
#define cpa "CPA"
#define iny "INY"
#define dec "DEC"
#define dex "DEX"
#define bne "BNE"
#define cld "CLD"
#define cpx "CPX"
#define sbc "SBC"
#define inc "INC"
#define inx "INX"
#define nop "NOP"
#define beq "BEQ"
#define sed "SED"

static const e6502_Instruction e6502_instructions[256] = {
    // 0x00
    [0b00000000] = {brk, adr_imp,   7},

    [0b00000001] = {ora, adr_ind_x, 6},
    [0b00000101] = {ora, adr_zp,    3},
    [0b00001001] = {ora, adr_imm,   2},
    [0b00001101] = {ora, adr_abs,   4},

    [0b00000110] = {asl, adr_zp,    5},
    [0b00001010] = {asl_a, adr_acc, 2},
    [0b00001110] = {asl, adr_abs,   6},

    [0b00001000] = {php, adr_imp,   3},

    // 0x10
    [0b00010000] = {bpl, adr_rel,   2},

    [0b00010001] = {ora, adr_ind_y, 5},
    [0b00010101] = {ora, adr_zp_x,  4},
    [0b00011001] = {ora, adr_abs_y, 4},
    [0b00011101] = {ora, adr_abs_x, 4},

    [0b00011000] = {clc, adr_imp,   2},

    [0b00010110] = {asl, adr_zp_x,  6},
    [0b00011110] = {asl, adr_abs_x, 7},

    // 0x20
    [0b00100000] = {jsr, adr_abs,   6},

    [0b00100100] = {bit, adr_zp,    3},
    [0b00101100] = {bit, adr_abs,   4},

    [0b00100001] = {and, adr_ind_x, 6},
    [0b00100101] = {and, adr_zp,    3},
    [0b00101001] = {and, adr_imm,   2},
    [0b00101101] = {and, adr_abs,   4},

    [0b00100110] = {rol, adr_zp,    5},
    [0b00101010] = {rol_a, adr_acc, 2},
    [0b00101110] = {rol, adr_abs,   6},

    [0b00101000] = {plp, adr_imp,   4},

    // 0x30
    [0b00110000] = {bmi, adr_rel,   2},

    [0b00110001] = {and, adr_ind_y, 5},
    [0b00110101] = {and, adr_zp_x,  4},
    [0b00111001] = {and, adr_abs_y, 3},
    [0b00111101] = {and, adr_abs_x, 3},

    [0b00110110] = {rol, adr_zp_x,  6},
    [0b00111110] = {rol, adr_abs_x, 7},

    [0b00111000] = {sec, adr_imp,   2},

    // 0x40
    [0b01000000] = {rti, adr_imp,   6},

    [0b01000001] = {eor, adr_ind_x, 6},
    [0b01000101] = {eor, adr_zp,    3},
    [0b01001001] = {eor, adr_imm,   2},
    [0b01001101] = {eor, adr_abs,   4},

    [0b01000110] = {lsr, adr_zp,    5},
    [0b01001010] = {lsr_a, adr_acc, 2},
    [0b01001110] = {lsr, adr_abs,   6},

    [0b01001000] = {pha, adr_imp,   3},

    [0b01001100] = {jmp, adr_abs,   3},

    // 0x50
    [0b01010000] = {bvc, adr_rel,   2},

    [0b01010001] = {eor, adr_ind_y, 5},
    [0b01010101] = {eor, adr_zp_x,  4},
    [0b01011001] = {eor, adr_abs_y, 4},
    [0b01011101] = {eor, adr_abs_x, 4},

    [0b01010110] = {lsr, adr_zp_x,  6},
    [0b01011110] = {lsr, adr_abs_x, 7},

    [0b01011000] = {cli, adr_imp,   2},

    // 0x60
    [0b01100000] = {rts, adr_imp,   6},

    [0b01100001] = {adc, adr_ind_x, 6},
    [0b01100101] = {adc, adr_zp,    3},
    [0b01101001] = {adc, adr_imm,   2},
    [0b01101101] = {adc, adr_abs,   4},

    [0b01100110] = {ror, adr_zp,    5},
    [0b01101010] = {ror_a, adr_acc, 2},
    [0b01101110] = {ror, adr_abs,   6},

    [0b01101000] = {pla, adr_imp,   4},

    [0b01101100] = {jmp, adr_ind,   5},

    // 0x70
    [0b01110000] = {bvs, adr_rel,   2},

    [0b01110001] = {adc, adr_ind_y, 5},
    [0b01110101] = {adc, adr_zp_x,  4},
    [0b01111001] = {adc, adr_abs_y, 4},
    [0b01111101] = {adc, adr_abs_x, 4},

    [0b01110110] = {ror, adr_zp_x,  6},
    [0b01111110] = {ror, adr_abs_x, 7},

    [0b01111000] = {sei, adr_imp,   2},

    // 0x80
    [0b10000001] = {sta, adr_ind_x, 6},
    [0b10000101] = {sta, adr_zp,    3},
    [0b10001101] = {sta, adr_abs,   4},

    [0b10000110] = {stx, adr_zp,    3},
    [0b10001110] = {stx, adr_abs,   4},

    [0b10000100] = {sty, adr_zp,    3},
    [0b10001100] = {sty, adr_abs,   4},

    [0b10001000] = {dey, adr_imp,   2},

    [0b10001010] = {txa, adr_imp,  2},

    // 0x90
    [0b10010000] = {bcc, adr_rel,   2},

    [0b10010001] = {sta, adr_ind_y, 6},
    [0b10010101] = {sta, adr_zp_x,  4},
    [0b10011001] = {sta, adr_abs_y, 5},
    [0b10011101] = {sta, adr_abs_x, 5},

    [0b10010110] = {stx, adr_zp_y,  4},

    [0b10010100] = {sty, adr_zp_x,  4},

    [0b10011000] = {tya, adr_imp,   2},
    [0b10011010] = {txs, adr_imp,   2},

    // 0xA0
    [0b10100001] = {lda, adr_ind_x, 6},
    [0b10100101] = {lda, adr_zp,    3},
    [0b10101001] = {lda, adr_imm,   2},
    [0b10101101] = {lda, adr_abs,   4},

    [0b10100010] = {ldx, adr_imm,   2},
    [0b10100110] = {ldx, adr_zp,    3},
    [0b10101110] = {ldx, adr_abs,   4},

    [0b10100000] = {ldy, adr_imm,   2},
    [0b10100100] = {ldy, adr_zp,    3},
    [0b10101100] = {ldy, adr_abs,   4},

    [0b10101010] = {tax, adr_imp,   2},
    [0b10101000] = {tay, adr_imp,   2},

    // 0xB0
    [0b10110000] = {bcs, adr_rel,   2},

    [0b10110001] = {lda, adr_ind_y, 5},
    [0b10110101] = {lda, adr_zp_x,  4},
    [0b10111001] = {lda, adr_abs_y, 4},
    [0b10111101] = {lda, adr_abs_x, 4},

    [0b10110110] = {ldx, adr_zp_y,  4},
    [0b10111110] = {ldx, adr_abs_y, 4},

    [0b10110100] = {ldy, adr_zp_x,  4},
    [0b10111100] = {ldy, adr_abs_x, 4},

    [0b10111000] = {clv, adr_imp,   2},

    [0b10111010] = {tsx, adr_imp,   2},

    // 0xC0
    [0b11000000] = {cpy, adr_imm,   2},
    [0b11000100] = {cpy, adr_zp,    3},
    [0b11001100] = {cpy, adr_abs,   4},

    [0b11000001] = {cpa, adr_ind_x, 6},
    [0b11000101] = {cpa, adr_zp,    3},
    [0b11001001] = {cpa, adr_imm,   2},
    [0b11001101] = {cpa, adr_abs,   4},

    [0b11001000] = {iny, adr_imp,   2},

    [0b11000110] = {dec, adr_zp,    5},
    [0b11001110] = {dec, adr_abs,   6},
    [0b11010110] = {dec, adr_zp_x,  6},
    [0b11011110] = {dec, adr_abs_x, 7},

    [0b11001010] = {dex, adr_imp,   2},

    // 0xD0
    [0b11010000] = {bne, adr_rel,   2},

    [0b11011000] = {cld, adr_imp,   2},

    [0b11010001] = {cpa, adr_ind_y, 5},
    [0b11010101] = {cpa, adr_zp_x,  4},
    [0b11011001] = {cpa, adr_abs_y, 4},
    [0b11011101] = {cpa, adr_abs_x, 4},

    // 0xE0
    [0b11100000] = {cpx, adr_imm,   2},
    [0b11100100] = {cpx, adr_zp,    3},
    [0b11101100] = {cpx, adr_abs,   4},

    [0b11100001] = {sbc, adr_ind_x, 6},
    [0b11100101] = {sbc, adr_zp,    3},
    [0b11101001] = {sbc, adr_imm,   2},
    [0b11101101] = {sbc, adr_abs,   4},

    [0b11100110] = {inc, adr_zp,    5},
    [0b11101110] = {inc, adr_abs,   6},

    [0b11101000] = {inx, adr_imp,   2},

    [0b11101010] = {nop, adr_imp,   2},

    // 0xF0
    [0b11110000] = {beq, adr_rel,   2},

    [0b11110001] = {sbc, adr_ind_y, 5},
    [0b11110101] = {sbc, adr_zp_x,  4},
    [0b11111001] = {sbc, adr_abs_y, 4},
    [0b11111101] = {sbc, adr_abs_x, 4},

    [0b11110110] = {inc, adr_zp_x,  6},
    [0b11111110] = {inc, adr_abs_x, 7},

    [0b11111000] = {sed, adr_imp,   2},

};

int e6502_fprintf_instr(FILE* file,
                        uint8_t opcode, uint8_t* operand) {
    int ret = 0;
    const e6502_Instruction* instr = &e6502_instructions[opcode];
    if (NULL == instr) {
        ret += fprintf(file, "ILLEGAL: $%02x", opcode);
    } else {
        ret += fputs(instr->operator, file);
        if (NULL != instr->mode) {
            char str[16] = {0};
            int len = instr->mode(operand, str, sizeof(str) - 1);
            ret += fprintf(file, " %.*s", len, str);
        }
    }
    return ret;
}