crater/src/disassembler/arguments.c

/* Copyright (C) 2014-2016 Ben Kurtovic <ben.kurtovic@gmail.com>
   Released under the terms of the MIT License. See LICENSE for details. */

#include <stddef.h>

#include "arguments.h"
#include "../logging.h"
#include "../util.h"

#define MAX_ARG_SIZE 256

/* Internal structs, enums, etc. */

typedef enum {
    AT_NONE = 0,
    /* Register */
    AT_REG_A,   AT_REG_B,   AT_REG_C,   AT_REG_D,   AT_REG_E,   AT_REG_H,
    AT_REG_L,   AT_REG_I,   AT_REG_R,   AT_REG_AF,  AT_REG_BC,  AT_REG_DE,
    AT_REG_HL,  AT_REG_IXY, AT_REG_SP,  AT_REG_AF_, AT_REG_IH,  AT_REG_IL,
    /* Immediate */
    AT_IMM_U16, AT_IMM_U8,  AT_IMM_REL, AT_IMM_BIT, AT_IMM_RST, AT_IMM_IM,
    /* Indirect */
    AT_IDR_HL,  AT_IDR_BC,  AT_IDR_DE,  AT_IDR_SP,  AT_IDR_IXY, AT_IDR_IMM,
    /* Indexed */
    AT_IX_IY,
    /* Condition */
    AT_COND_NZ, AT_COND_Z,  AT_COND_NC, AT_COND_C,  AT_COND_PO, AT_COND_PE,
    AT_COND_P,  AT_COND_M,
    /* Port */
    AT_PORT_C,  AT_PORT_IM, AT_PORT_0
} ArgType;

typedef ArgType ArgTable[3][256];

typedef struct {
    uint8_t index, opcode, arg1, arg2;
    ArgTable *table;
} Instr;

/* Temporary aliases to make table definitions concise */

#define __ AT_NONE
#define A_ AT_REG_A
#define B_ AT_REG_B
#define C_ AT_REG_C
#define D_ AT_REG_D
#define E_ AT_REG_E
#define H_ AT_REG_H
#define L_ AT_REG_L
#define I_ AT_REG_I
#define R_ AT_REG_R
#define AF AT_REG_AF
#define BC AT_REG_BC
#define DE AT_REG_DE
#define HL AT_REG_HL
#define XY AT_REG_IXY
#define SP AT_REG_SP
#define AS AT_REG_AF_
#define IH AT_REG_IH
#define IL AT_REG_IL
#define M2 AT_IMM_U16
#define M1 AT_IMM_U8
#define ML AT_IMM_REL
#define MB AT_IMM_BIT
#define MR AT_IMM_RST
#define MI AT_IMM_IM
#define NH AT_IDR_HL
#define NB AT_IDR_BC
#define ND AT_IDR_DE
#define NS AT_IDR_SP
#define NI AT_IDR_IXY
#define NM AT_IDR_IMM
#define II AT_IX_IY
#define NZ AT_COND_NZ
#define Z_ AT_COND_Z
#define NC AT_COND_NC
#define CC AT_COND_C
#define PO AT_COND_PO
#define PE AT_COND_PE
#define P_ AT_COND_P
#define M_ AT_COND_M
#define PC AT_PORT_C
#define PM AT_PORT_IM
#define R0 AT_PORT_0

/* Argument tables */

static ArgTable instr_args = {
    {
        __, BC, NB, BC, B_, B_, B_, __, AF, HL, A_, BC, C_, C_, C_, __,
        ML, DE, ND, DE, D_, D_, D_, __, ML, HL, A_, DE, E_, E_, E_, __,
        NZ, HL, NM, HL, H_, H_, H_, __, Z_, HL, HL, HL, L_, L_, L_, __,
        NC, SP, NM, SP, NH, NH, NH, __, CC, HL, A_, SP, A_, A_, A_, __,
        B_, B_, B_, B_, B_, B_, B_, B_, C_, C_, C_, C_, C_, C_, C_, C_,
        D_, D_, D_, D_, D_, D_, D_, D_, E_, E_, E_, E_, E_, E_, E_, E_,
        H_, H_, H_, H_, H_, H_, H_, H_, L_, L_, L_, L_, L_, L_, L_, L_,
        NH, NH, NH, NH, NH, NH, __, NH, A_, A_, A_, A_, A_, A_, A_, A_,
        A_, A_, A_, A_, A_, A_, A_, A_, A_, A_, A_, A_, A_, A_, A_, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, A_, A_, A_, A_, A_, A_, A_, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        NZ, BC, NZ, M2, NZ, BC, A_, MR, Z_, __, Z_, __, Z_, M2, A_, MR,
        NC, DE, NC, PM, NC, DE, M1, MR, CC, __, CC, A_, CC, __, A_, MR,
        PO, HL, PO, NS, PO, HL, M1, MR, PE, NH, PE, DE, PE, __, M1, MR,
        P_, AF, P_, __, P_, AF, M1, MR, M_, SP, M_, __, M_, __, M1, MR
    },
    {
        __, M2, A_, __, __, __, M1, __, AS, BC, NB, __, __, __, M1, __,
        __, M2, A_, __, __, __, M1, __, __, DE, ND, __, __, __, M1, __,
        ML, M2, HL, __, __, __, M1, __, ML, HL, NM, __, __, __, M1, __,
        ML, M2, A_, __, __, __, M1, __, ML, SP, NM, __, __, __, M1, __,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        __, __, __, __, __, __, __, __, B_, C_, D_, E_, H_, L_, NH, A_,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, M2, __, M2, __, M1, __, __, __, M2, __, M2, __, M1, __,
        __, __, M2, A_, M2, __, __, __, __, __, M2, PM, M2, __, M1, __,
        __, __, M2, HL, M2, __, __, __, __, __, M2, HL, M2, __, __, __,
        __, __, M2, __, M2, __, __, __, __, HL, M2, __, M2, __, __, __
    },
    { __ }
};

static ArgTable instr_args_extended = {
    {
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        B_, PC, HL, NM, __, __, MI, I_, C_, PC, HL, BC, __, __, MI, R_,
        D_, PC, HL, NM, __, __, MI, A_, E_, PC, HL, DE, __, __, MI, A_,
        H_, PC, HL, NM, __, __, MI, __, L_, PC, HL, HL, __, __, MI, __,
        PC, PC, HL, NM, __, __, MI, __, A_, PC, HL, SP, __, __, MI, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __
    },
    {
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        PC, B_, BC, BC, __, __, __, A_, PC, C_, BC, NM, __, __, __, A_,
        PC, D_, DE, DE, __, __, __, I_, PC, E_, DE, NM, __, __, __, R_,
        PC, H_, HL, HL, __, __, __, __, PC, L_, HL, NM, __, __, __, __,
        __, R0, SP, SP, __, __, __, __, PC, A_, SP, NM, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __
    },
    { __ }
};

static ArgTable instr_args_bits = {
    {
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB
    },
    {
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_,
        B_, C_, D_, E_, H_, L_, NH, A_, B_, C_, D_, E_, H_, L_, NH, A_
    },
    { __ }
};

static ArgTable instr_args_index = {
    {
        __, __, __, __, __, __, __, __, __, XY, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, XY, __, __, __, __, __, __,
        __, XY, NM, XY, IH, IH, IH, __, __, XY, XY, XY, IL, IL, IL, __,
        __, __, __, __, II, II, II, __, __, XY, __, __, __, __, __, __,
        __, __, __, __, B_, B_, B_, __, __, __, __, __, C_, C_, C_, __,
        __, __, __, __, D_, D_, D_, __, __, __, __, __, E_, E_, E_, __,
        IH, IH, IH, IH, IH, IH, H_, IH, IL, IL, IL, IL, IL, IL, L_, IL,
        II, II, II, II, II, II, __, II, __, __, __, __, A_, A_, A_, __,
        __, __, __, __, A_, A_, A_, __, __, __, __, __, A_, A_, A_, __,
        __, __, __, __, IH, IL, II, __, __, __, __, __, A_, A_, A_, __,
        __, __, __, __, IH, IL, II, __, __, __, __, __, IH, IL, II, __,
        __, __, __, __, IH, IL, II, __, __, __, __, __, IH, IL, II, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, XY, __, NS, __, XY, __, __, __, NI, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, SP, __, __, __, __, __, __
    },
    {
        __, __, __, __, __, __, __, __, __, BC, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, DE, __, __, __, __, __, __,
        __, M2, XY, __, __, __, M1, __, __, XY, NM, __, __, __, M1, __,
        __, __, __, __, __, __, M1, __, __, SP, __, __, __, __, __, __,
        __, __, __, __, IH, IL, II, __, __, __, __, __, IH, IL, II, __,
        __, __, __, __, IH, IL, II, __, __, __, __, __, IH, IL, II, __,
        B_, C_, D_, E_, IH, IL, II, A_, B_, C_, D_, E_, IH, IL, II, A_,
        B_, C_, D_, E_, H_, L_, __, A_, __, __, __, __, IH, IL, II, __,
        __, __, __, __, IH, IL, II, __, __, __, __, __, IH, IL, II, __,
        __, __, __, __, __, __, __, __, __, __, __, __, IH, IL, II, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, XY, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, XY, __, __, __, __, __, __
    },
    { __ }
};

static ArgTable instr_args_index_bits = {
    {
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB,
        MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB, MB
    },
    {
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II,
        II, II, II, II, II, II, II, II, II, II, II, II, II, II, II, II
    },
    {
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_,
        B_, C_, D_, E_, H_, L_, __, A_, B_, C_, D_, E_, H_, L_, __, A_
    }
};

/* Remove temporary aliases */

#undef __
#undef A_
#undef B_
#undef C_
#undef D_
#undef E_
#undef H_
#undef L_
#undef I_
#undef R_
#undef AF
#undef BC
#undef DE
#undef HL
#undef XY
#undef SP
#undef AS
#undef IH
#undef IL
#undef M2
#undef M1
#undef ML
#undef MB
#undef MR
#undef MI
#undef NH
#undef NB
#undef ND
#undef NS
#undef NI
#undef NM
#undef II
#undef NZ
#undef Z_
#undef NC
#undef CC
#undef PO
#undef PE
#undef P_
#undef M_
#undef PC
#undef PM
#undef R0

/*
    Decode an immediate argument.
*/
static void decode_immediate(char *arg, Instr *instr, ArgType type)
{
    uint8_t op = instr->opcode, take;
    bool ix = instr->index == 0xDD;

    switch (type) {
        case AT_IMM_U16:  // 16-bit immediate
            sprintf(arg, "$%04X", instr->arg1 + (instr->arg2 << 8));
            break;
        case AT_IMM_U8:  // 8-bit unsigned immediate
            if (instr->index != 0x00 && op == 0x36)
                take = instr->arg2;
            else
                take = instr->arg1;
            sprintf(arg, "$%02X", take);
            break;
        case AT_IMM_REL:  // 8-bit relative offset (JP and DJNZ)
            sprintf(arg, "%hhd", (int8_t) (instr->arg1 + 2));
            break;
        case AT_IMM_BIT:  // Bit position
            sprintf(arg, "%d", (op & 0x38) >> 3);
            break;
        case AT_IMM_RST:  // Reset
            sprintf(arg, "$%02X", op & 0x38);
            break;
        case AT_IMM_IM:  // Interrupt mode
            sprintf(arg, "%d", !(op & (1 << 4)) ? 0 : !(op & (1 << 3)) ? 1 : 2);
            break;
        case AT_IDR_IMM:  // Indirect immediate
            sprintf(arg, "($%04X)", instr->arg1 + (instr->arg2 << 8));
            break;
        case AT_IX_IY:  // Indexed offset
            if (instr->arg1) {
                char *format = ix ? "(ix%+hhd)" : "(iy%+hhd)";
                sprintf(arg, format, (int8_t) instr->arg1);
            } else {
                sprintf(arg, ix ? "(ix)" : "(iy)");
            }
            break;
        case AT_PORT_IM:  // Immediate port
            sprintf(arg, "($%02X)", instr->arg1);
            break;
        default:
            FATAL("invalid call: decode_immediate(arg, ..., %d)", type)
            return;
    }
}

/*
    Decode a single argument, given its type.
*/
static void decode_argument(char *arg, Instr *instr, ArgType type)
{
    const char *value;
    bool ix = instr->index == 0xDD;

    switch (type) {
        case AT_NONE:
            arg[0] = '\0';
            return;
        case AT_REG_A:   value = "a";    break;
        case AT_REG_B:   value = "b";    break;
        case AT_REG_C:   value = "c";    break;
        case AT_REG_D:   value = "d";    break;
        case AT_REG_E:   value = "e";    break;
        case AT_REG_H:   value = "h";    break;
        case AT_REG_L:   value = "l";    break;
        case AT_REG_I:   value = "i";    break;
        case AT_REG_R:   value = "r";    break;
        case AT_REG_AF:  value = "af";   break;
        case AT_REG_BC:  value = "bc";   break;
        case AT_REG_DE:  value = "de";   break;
        case AT_REG_HL:  value = "hl";   break;
        case AT_REG_SP:  value = "sp";   break;
        case AT_REG_AF_: value = "af'";  break;
        case AT_IDR_HL:  value = "(hl)"; break;
        case AT_IDR_BC:  value = "(bc)"; break;
        case AT_IDR_DE:  value = "(de)"; break;
        case AT_IDR_SP:  value = "(sp)"; break;
        case AT_COND_NZ: value = "nz";   break;
        case AT_COND_Z:  value = "z";    break;
        case AT_COND_NC: value = "nc";   break;
        case AT_COND_C:  value = "c";    break;
        case AT_COND_PO: value = "po";   break;
        case AT_COND_PE: value = "pe";   break;
        case AT_COND_P:  value = "p";    break;
        case AT_COND_M:  value = "m";    break;
        case AT_PORT_C:  value = "(c)";  break;
        case AT_PORT_0:  value = "0";    break;
        case AT_REG_IXY: value = ix ? "ix"   : "iy";   break;
        case AT_REG_IH:  value = ix ? "ixh"  : "iyh";  break;
        case AT_REG_IL:  value = ix ? "ixl"  : "iyl";  break;
        case AT_IDR_IXY: value = ix ? "(ix)" : "(iy)"; break;
        case AT_IMM_U16:
        case AT_IMM_U8:
        case AT_IMM_REL:
        case AT_IMM_BIT:
        case AT_IMM_RST:
        case AT_IMM_IM:
        case AT_IDR_IMM:
        case AT_IX_IY:
        case AT_PORT_IM:
            decode_immediate(arg, instr, type);
            return;
        default:
            FATAL("invalid call: decode_argument(arg, ..., %d)", type)
            return;
    }
    strcpy(arg, value);
}

/*
    Fill an Instruction object with the appropriate fields.
*/
static inline void load_instr(Instr *instr, const uint8_t *bytes)
{
    uint8_t b = bytes[0];
    bool extend   = b == 0xED;
    bool bit      = b == 0xCB;
    bool index    = b == 0xDD || b == 0xFD;
    bool indexbit = index && bytes[1] == 0xCB;

    instr->index = index ? b : 0x00;

    if (indexbit) {
        instr->opcode = bytes[3];
        instr->arg1   = bytes[2];
    } else if (extend || bit || index) {
        instr->opcode = bytes[1];
        instr->arg1   = bytes[2];
        instr->arg2   = bytes[3];
    } else {
        instr->opcode = bytes[0];
        instr->arg1   = bytes[1];
        instr->arg2   = bytes[2];
    }

    if (extend)
        instr->table = &instr_args_extended;
    else if (bit)
        instr->table = &instr_args_bits;
    else if (indexbit)
        instr->table = &instr_args_index_bits;
    else if (index)
        instr->table = &instr_args_index;
    else
        instr->table = &instr_args;
}

/*
    Extract the arguments for the given instruction.

    The return value must be free()d.
*/
char* decode_arguments(const uint8_t *bytes)
{
    char args[3][MAX_ARG_SIZE], *result;
    Instr instr;
    ArgType type;
    size_t i, len;

    load_instr(&instr, bytes);
    for (i = 0; i < 3; i++) {
        type = (*instr.table)[i][instr.opcode];
        decode_argument(args[i], &instr, type);
    }

    if (!*args[0])
        return NULL;
    if (!*args[1])
        return cr_strdup(args[0]);

    // Two or three arguments; need to add commas:
    len = strlen(args[0]) + strlen(args[1]) + strlen(args[2]);
    result = malloc(sizeof(char) * (len + 2 * (*args[2] ? 3 : 2) + 1));
    if (*args[2])
        sprintf(result, "%s, %s, %s", args[0], args[1], args[2]);
    else
        sprintf(result, "%s, %s", args[0], args[1]);
    return result;
}