6502.c

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

#define ADDR_MODE_COUNT 13

enum instr {
        ADC, AND, ASL,
        BCC, BCS, BEQ, BIT, BMI, BNE, BPL, BRK, BVC, BVS,
        CLC, CLD, CLI, CLV, CMP, CPX, CPY,
        DEC, DEX, DEY,
        EOR,
        INC, INX, INY,
        JMP, JSR,
        LDA, LDX, LDY, LSR,
        NOP,
        ORA,
        PHA, PHP, PLA, PLP,
        ROL, ROR, RTI, RTS,
        SBC, SEC, SED, SEI, STA, STX, STY,
        TAX, TAY, TSX, TXA, TXS, TYA, _ICOUNT
};

const char *strmap[] = {
        "ADC", "AND", "ASL",
        "BCC", "BCS", "BEQ", "BIT", "BMI", "BNE", "BPL", "BRK", "BVC", "BVS",
        "CLC", "CLD", "CLI", "CLV", "CMP", "CPX", "CPY",
        "DEC", "DEX", "DEY",
        "EOR",
        "INC", "INX", "INY",
        "JMP", "JSR",
        "LDA", "LDX", "LDY", "LSR",
        "NOP",
        "ORA",
        "PHA", "PHP", "PLA", "PLP",
        "ROL", "ROR", "RTI", "RTS",
        "SBC", "SEC", "SED", "SEI", "STA", "STX", "STY",
        "TAX", "TAY", "TSX", "TXA", "TXS", "TYA", 
};

// 0xFF - Invalid addressing mode
// Addressing modes in this order:
//      Acc  Abs  AbX  AbY  Imm  Imp  Ind  Xnd  InY  Rel  Zpg  ZpX  ZpY
const uint8_t opctbl[] = {
/*ADC*/ 0xFF,0x6D,0x7D,0x79,0x69,0xFF,0xFF,0x61,0x71,0xFF,0x65,0x75,0xFF,
/*AND*/ 0xFF,0x2D,0x3D,0x39,0x29,0xFF,0xFF,0x21,0x31,0xFF,0x25,0x35,0xFF,
/*ASL*/ 0x0A,0x0E,0x1E,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x06,0x16,0xFF,
/*BCC*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x90,0xFF,0xFF,0xFF,
/*BCS*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xB0,0xFF,0xFF,0xFF,
/*BEQ*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xF0,0xFF,0xFF,0xFF,
/*BIT*/ 0xFF,0x2C,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x24,0xFF,0xFF,
/*BMI*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x30,0xFF,0xFF,0xFF,
/*BNE*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xD0,0xFF,0xFF,0xFF,
/*BPL*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x10,0xFF,0xFF,0xFF,
/*BRK*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*BVC*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x50,0xFF,0xFF,0xFF,
/*BVS*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x70,0xFF,0xFF,0xFF,
/*CLC*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x18,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*CLD*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xD8,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*CLI*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x58,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*CLV*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xB8,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*CMP*/ 0xFF,0xCD,0xDD,0xD9,0xC9,0xFF,0xFF,0xC1,0xD1,0xFF,0xC5,0xD5,0xFF,
/*CPX*/ 0xFF,0xEC,0xFF,0xFF,0xE0,0xFF,0xFF,0xFF,0xFF,0xFF,0xE4,0xFF,0xFF,
/*CPY*/ 0xFF,0xCC,0xFF,0xFF,0xC0,0xFF,0xFF,0xFF,0xFF,0xFF,0xC4,0xFF,0xFF,
/*DEC*/ 0xFF,0xCE,0xDE,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xC6,0xD6,0xFF,
/*DEX*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xCA,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*DEY*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x88,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*EOR*/ 0xFF,0x4D,0x5D,0x59,0x49,0xFF,0xFF,0x41,0x51,0xFF,0x45,0x55,0xFF,
/*INC*/ 0xFF,0xEE,0xFE,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xE6,0xF6,0xFF,
/*INX*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xE8,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*INY*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xC8,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*JMP*/ 0xFF,0x4C,0xFF,0xFF,0xFF,0xFF,0x6C,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*JSR*/ 0xFF,0x20,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*LDA*/ 0xFF,0xAD,0xBD,0xB9,0xA9,0xFF,0xFF,0xA1,0xB1,0xFF,0xA5,0xB5,0xFF,
/*LDX*/ 0xFF,0xAE,0xFF,0xBE,0xA2,0xFF,0xFF,0xFF,0xFF,0xFF,0xA6,0xFF,0xB6,
/*LDY*/ 0xFF,0xAC,0xBC,0xFF,0xA0,0xFF,0xFF,0xFF,0xFF,0xFF,0xA4,0xB4,0xFF,
/*LSR*/ 0x4A,0x4E,0x5E,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x46,0x56,0xFF,
/*NOP*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xEA,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*ORA*/ 0xFF,0x0D,0x1D,0x19,0x09,0xFF,0xFF,0x01,0x11,0xFF,0x05,0x15,0xFF,
/*PHA*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x48,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*PHP*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x08,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*PLA*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x68,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*PLP*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x28,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*ROL*/ 0x2A,0x2E,0x3E,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x26,0x36,0xFF,
/*ROR*/ 0x6A,0x6E,0x7E,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x66,0x76,0xFF,
/*RTI*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x40,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*RTS*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x60,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*SBC*/ 0xFF,0xED,0xFD,0xF9,0xE9,0xFF,0xFF,0xE1,0xF1,0xFF,0xE5,0xF5,0xFF,
/*SEC*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x38,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*SED*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xF8,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*SEI*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x78,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*STA*/ 0xFF,0x8D,0x9D,0x99,0xFF,0xFF,0xFF,0x81,0x91,0xFF,0x85,0x95,0xFF,
/*STX*/ 0xFF,0x8E,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x86,0xFF,0x96,
/*STY*/ 0xFF,0x8C,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x84,0x94,0xFF,
/*TAX*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xAA,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*TAY*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xA8,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*TSX*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0xBA,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*TXA*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x8A,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*TXS*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x9A,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
/*TYA*/ 0xFF,0xFF,0xFF,0xFF,0xFF,0x98,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
};

uint8_t instrtbl[256];
uint8_t addrtbl[256];

uint8_t *data;
void p_acc() { printf("A"); }
void p_abs() { printf("$%04X", ((uint16_t*)data)[0]); data += 2; }
void p_abx() { printf("$%04X,X", ((uint16_t*)data)[0]); data += 2; }
void p_aby() { printf("$%04X,Y", ((uint16_t*)data)[0]); data += 2; }
void p_imm() { printf("#$%02X", data[0]); data += 1; }
void p_imp() { }
void p_ind() { printf("($%04X)", ((uint16_t*)data)[0]); data += 2; }
void p_xnd() { printf("($%02X,X)", data[0]); data += 1; }
void p_iny() { printf("($%02X),Y", data[0]); data += 1; }
void p_rel() { printf("$%02X", data[0]); data += 1; }
void p_zpg() { printf("$%02X", data[0]); data += 1; }
void p_zpx() { printf("$%02X,X", data[0]); data += 1; }
void p_zpy() { printf("$%02X,Y", data[0]); data += 1; }

void (*printers[])() = { p_acc, p_abs, p_abx, p_aby, p_imm, p_imp, p_ind, p_xnd, p_iny, p_rel, p_zpg, p_zpx, p_zpy };

int main(int argc, char **argv) {
        if (argc != 2) {
                fprintf(stderr, "Usage: %s <6502 binary>\n", argv[0]);
                return 1;
        }
        FILE *fp = fopen(argv[1], "rb");
        if (!fp) {
                perror(argv[1]);
                return 1;
        }
        fseek(fp, 0, SEEK_END);
        size_t fsize = ftell(fp);
        fseek(fp, 0, SEEK_SET);
        uint8_t *mem = malloc(fsize);
        fread(mem, 1, fsize, fp);
        fclose(fp);

        data = mem;

        memset(instrtbl, 0xFF, sizeof(instrtbl));
        memset(addrtbl, 0xFF, sizeof(addrtbl));
        for (int i = 0; i < ADDR_MODE_COUNT*_ICOUNT; i++) {
                if (opctbl[i] != 0xFF) {
                        instrtbl[opctbl[i]] = i/ADDR_MODE_COUNT;
                        addrtbl[opctbl[i]] = i%ADDR_MODE_COUNT;
                }
        }

        while (data-mem < fsize) {
                uint8_t opc = *data++;
                if (instrtbl[opc] == 0xFF) {
                        printf("Invalid instruction: $%X\n", opc);
                        break;
                }
                if (addrtbl[opc] == 0xFF) {
                        printf("Invalid addressing mode for %s\n", strmap[instrtbl[opc]]);
                        break;
                }
                printf("%s ", strmap[instrtbl[opc]]);
                printers[addrtbl[opc]]();
                printf("\n");
        }
}