bsnes/Core/sm83_cpu.c

#include <stdio.h>
#include <stdbool.h>
#include <assert.h>
#include "gb.h"


typedef void GB_opcode_t(GB_gameboy_t *gb, uint8_t opcode);

typedef enum {
    /* Default behavior. If the CPU writes while another component reads, it reads the old value */
    GB_CONFLICT_READ_OLD,
    /* If the CPU writes while another component reads, it reads the new value */
    GB_CONFLICT_READ_NEW,
    /* If the CPU and another component write at the same time, the CPU's value "wins" */
    GB_CONFLICT_WRITE_CPU,
    /* Register specific values */
    GB_CONFLICT_STAT_CGB,
    GB_CONFLICT_STAT_DMG,
    GB_CONFLICT_PALETTE_DMG,
    GB_CONFLICT_PALETTE_CGB,
    GB_CONFLICT_READ_DMG_LCDC,
} GB_conflict_t;

/* Todo: How does double speed mode affect these? */
static const GB_conflict_t cgb_conflict_map[0x80] = {
    [GB_IO_IF] = GB_CONFLICT_WRITE_CPU,
    [GB_IO_LYC] = GB_CONFLICT_WRITE_CPU,
    [GB_IO_STAT] = GB_CONFLICT_STAT_CGB,
    [GB_IO_BGP] = GB_CONFLICT_PALETTE_CGB,
    [GB_IO_OBP0] = GB_CONFLICT_PALETTE_CGB,
    [GB_IO_OBP1] = GB_CONFLICT_PALETTE_CGB,
    

    /* Todo: most values not verified, and probably differ between revisions */
};

/* Todo: verify on an MGB */
static const GB_conflict_t dmg_conflict_map[0x80] = {
    [GB_IO_IF] = GB_CONFLICT_WRITE_CPU,
    [GB_IO_LYC] = GB_CONFLICT_READ_OLD,
    [GB_IO_LCDC] = GB_CONFLICT_READ_DMG_LCDC,
    [GB_IO_SCY] = GB_CONFLICT_READ_NEW,
    [GB_IO_STAT] = GB_CONFLICT_STAT_DMG,
 
    [GB_IO_BGP] = GB_CONFLICT_PALETTE_DMG,
    [GB_IO_OBP0] = GB_CONFLICT_PALETTE_DMG,
    [GB_IO_OBP1] = GB_CONFLICT_PALETTE_DMG,
    
    /* Todo: these were not verified at all */
    [GB_IO_WY] = GB_CONFLICT_READ_NEW,
    [GB_IO_WX] = GB_CONFLICT_READ_NEW,
    [GB_IO_SCX] = GB_CONFLICT_READ_NEW,
};

/* Todo: Verify on an SGB1 */
static const GB_conflict_t sgb_conflict_map[0x80] = {
    [GB_IO_IF] = GB_CONFLICT_WRITE_CPU,
    [GB_IO_LYC] = GB_CONFLICT_READ_OLD,
    [GB_IO_LCDC] = GB_CONFLICT_READ_NEW,
    [GB_IO_SCY] = GB_CONFLICT_READ_NEW,
    [GB_IO_STAT] = GB_CONFLICT_STAT_DMG,
    
    [GB_IO_BGP] = GB_CONFLICT_READ_NEW,
    [GB_IO_OBP0] = GB_CONFLICT_READ_NEW,
    [GB_IO_OBP1] = GB_CONFLICT_READ_NEW,
    
    /* Todo: these were not verified at all */
    [GB_IO_WY] = GB_CONFLICT_READ_NEW,
    [GB_IO_WX] = GB_CONFLICT_READ_NEW,
    [GB_IO_SCX] = GB_CONFLICT_READ_NEW,
};

static uint8_t cycle_read(GB_gameboy_t *gb, uint16_t addr)
{
    if (gb->pending_cycles) {
        GB_advance_cycles(gb, gb->pending_cycles);
    }
    uint8_t ret = GB_read_memory(gb, addr);
    gb->pending_cycles = 4;
    return ret;
}

static uint8_t cycle_read_inc_oam_bug(GB_gameboy_t *gb, uint16_t addr)
{
    if (gb->pending_cycles) {
        GB_advance_cycles(gb, gb->pending_cycles);
    }
    GB_trigger_oam_bug_read_increase(gb, addr); /* Todo: test T-cycle timing */
    uint8_t ret = GB_read_memory(gb, addr);
    gb->pending_cycles = 4;
    return ret;
}

/* A special case for IF during ISR, returns the old value of IF. */
/* TODO: Verify the timing, it might be wrong in cases where, in the same M cycle, IF
   is both read be the CPU, modified by the ISR, and modified by an actual interrupt.
   If this timing proves incorrect, the ISR emulation must be updated so IF reads are
   timed correctly. */
static uint8_t cycle_write_if(GB_gameboy_t *gb, uint8_t value)
{
    assert(gb->pending_cycles);
    GB_advance_cycles(gb, gb->pending_cycles);
    uint8_t old = (gb->io_registers[GB_IO_IF]) & 0x1F;
    GB_write_memory(gb, 0xFF00 + GB_IO_IF, value);
    gb->pending_cycles = 4;
    return old;
}

static void cycle_write(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
{
    assert(gb->pending_cycles);
    GB_conflict_t conflict = GB_CONFLICT_READ_OLD;
    if ((addr & 0xFF80) == 0xFF00) {
        const GB_conflict_t *map = NULL;
        if (GB_is_cgb(gb)) {
            map = cgb_conflict_map;
        }
        else if (GB_is_sgb(gb)) {
            map = sgb_conflict_map;
        }
        else {
            map = dmg_conflict_map;
        }
        conflict = map[addr & 0x7F];
    }
    switch (conflict) {
        case GB_CONFLICT_READ_OLD:
            GB_advance_cycles(gb, gb->pending_cycles);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 4;
            return;
            
        case GB_CONFLICT_READ_NEW:
            GB_advance_cycles(gb, gb->pending_cycles - 1);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 5;
            return;
            
        case GB_CONFLICT_WRITE_CPU:
            GB_advance_cycles(gb, gb->pending_cycles + 1);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 3;
            return;
        
        /* The DMG STAT-write bug is basically the STAT register being read as FF for a single T-cycle */
        case GB_CONFLICT_STAT_DMG:
            GB_advance_cycles(gb, gb->pending_cycles);
            /* State 7 is the edge between HBlank and OAM mode, and it behaves a bit weird.
             The OAM interrupt seems to be blocked by HBlank interrupts in that case, despite
             the timing not making much sense for that.
             This is a hack to simulate this effect */
            if (gb->display_state == 7 && (gb->io_registers[GB_IO_STAT] & 0x28) == 0x08) {
                GB_write_memory(gb, addr, ~0x20);
            }
            else {
                GB_write_memory(gb, addr, 0xFF);
            }
            GB_advance_cycles(gb, 1);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 3;
            return;
        
        case GB_CONFLICT_STAT_CGB: {
            /* Todo: Verify this with SCX adjustments */
            /* The LYC bit behaves differently */
            uint8_t old_value = GB_read_memory(gb, addr);
            GB_advance_cycles(gb, gb->pending_cycles);
            GB_write_memory(gb, addr, (old_value & 0x40) | (value & ~0x40));
            GB_advance_cycles(gb, 1);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 3;
            return;
        }
        
        /* There is some "time travel" going on with these two values, as it appears
           that there's some off-by-1-T-cycle timing issue in the PPU implementation.
         
           This is should be accurate for every measureable scenario, though. */
            
        case GB_CONFLICT_PALETTE_DMG: {
            GB_advance_cycles(gb, gb->pending_cycles - 2);
            uint8_t old_value = GB_read_memory(gb, addr);
            GB_write_memory(gb, addr, value | old_value);
            GB_advance_cycles(gb, 1);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 5;
            return;
        }
            
        case GB_CONFLICT_PALETTE_CGB: {
            GB_advance_cycles(gb, gb->pending_cycles - 2);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 6;
            return;
        }
            
        case GB_CONFLICT_READ_DMG_LCDC: {
            /* Seems to be affected by screen? Both my DMG (B, blob) and Game Boy Light behave this way though. */
            uint8_t old_value = GB_read_memory(gb, addr);
            GB_advance_cycles(gb, gb->pending_cycles - 2);
            GB_write_memory(gb, addr, old_value | (value & 1));
            GB_advance_cycles(gb, 1);
            GB_write_memory(gb, addr, value);
            gb->pending_cycles = 5;
            return;
        }
    }
}

static void cycle_no_access(GB_gameboy_t *gb)
{
    gb->pending_cycles += 4;
}

static void cycle_oam_bug(GB_gameboy_t *gb, uint8_t register_id)
{
    if (GB_is_cgb(gb)) {
        /* Slight optimization */
        gb->pending_cycles += 4;
        return;
    }
    if (gb->pending_cycles) {
        GB_advance_cycles(gb, gb->pending_cycles);
    }
    GB_trigger_oam_bug(gb, gb->registers[register_id]); /* Todo: test T-cycle timing */
    gb->pending_cycles = 4;

}

static void flush_pending_cycles(GB_gameboy_t *gb)
{
    if (gb->pending_cycles) {
        GB_advance_cycles(gb, gb->pending_cycles);
    }
    gb->pending_cycles = 0;
}

/* Todo: test if multi-byte opcodes trigger the OAM bug correctly */

static void ill(GB_gameboy_t *gb, uint8_t opcode)
{
    GB_log(gb, "Illegal Opcode. Halting.\n");
    gb->interrupt_enable = 0;
    gb->halted = true;
}

static void nop(GB_gameboy_t *gb, uint8_t opcode)
{
}

static void enter_stop_mode(GB_gameboy_t *gb)
{
    gb->stopped = true;
    gb->oam_ppu_blocked = !gb->oam_read_blocked;
    gb->vram_ppu_blocked = !gb->vram_read_blocked;
    gb->cgb_palettes_ppu_blocked = !gb->cgb_palettes_blocked;
}

static void leave_stop_mode(GB_gameboy_t *gb)
{
    /* The CPU takes more time to wake up then the other components */
    for (unsigned i = 0x200; i--;) {
        GB_advance_cycles(gb, 0x10);
    }
    gb->stopped = false;
    gb->oam_ppu_blocked = false;
    gb->vram_ppu_blocked = false;
    gb->cgb_palettes_ppu_blocked = false;
}

static void stop(GB_gameboy_t *gb, uint8_t opcode)
{
    if (gb->io_registers[GB_IO_KEY1] & 0x1) {
        flush_pending_cycles(gb);
        bool needs_alignment = false;
        
        GB_advance_cycles(gb, 0x4);
        /* Make sure we keep the CPU ticks aligned correctly when returning from double speed mode */
        if (gb->double_speed_alignment & 7) {
            GB_advance_cycles(gb, 0x4);
            needs_alignment = true;
        }

        gb->cgb_double_speed ^= true;
        gb->io_registers[GB_IO_KEY1] = 0;
        
        enter_stop_mode(gb);
        leave_stop_mode(gb);
        
        if (!needs_alignment) {
            GB_advance_cycles(gb, 0x4);
        }
        
    }
    else {
        GB_timing_sync(gb);
        if ((gb->io_registers[GB_IO_JOYP] & 0xF) != 0xF) {
            /* HW Bug? When STOP is executed while a button is down, the CPU halts forever
               yet the other hardware keeps running. */
            gb->interrupt_enable = 0;
            gb->halted = true;
        }
        else {
            enter_stop_mode(gb);
        }
    }
    
    /* Todo: is PC being actually read? */
    gb->pc++;
}

/* Operand naming conventions for functions:
   r = 8-bit register
   lr = low 8-bit register
   hr = high 8-bit register
   rr = 16-bit register
   d8 = 8-bit imm
   d16 = 16-bit imm
   d.. = [..]
   cc = condition code (z, nz, c, nc)
   */

static void ld_rr_d16(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    uint16_t value;
    register_id = (opcode >> 4) + 1;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    value |= cycle_read_inc_oam_bug(gb, gb->pc++) << 8;
    gb->registers[register_id] = value;
}

static void ld_drr_a(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = (opcode >> 4) + 1;
    cycle_write(gb, gb->registers[register_id], gb->registers[GB_REGISTER_AF] >> 8);
}

static void inc_rr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id = (opcode >> 4) + 1;
    cycle_oam_bug(gb, register_id);
    gb->registers[register_id]++;
}

static void inc_hr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = ((opcode >> 4) + 1) & 0x03;
    gb->registers[register_id] += 0x100;
    gb->registers[GB_REGISTER_AF] &= ~(GB_SUBTRACT_FLAG | GB_ZERO_FLAG | GB_HALF_CARRY_FLAG);

    if ((gb->registers[register_id] & 0x0F00) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((gb->registers[register_id] & 0xFF00) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}
static void dec_hr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = ((opcode >> 4) + 1) & 0x03;
    gb->registers[register_id] -= 0x100;
    gb->registers[GB_REGISTER_AF] &= ~(GB_ZERO_FLAG | GB_HALF_CARRY_FLAG);
    gb->registers[GB_REGISTER_AF] |= GB_SUBTRACT_FLAG;

    if ((gb->registers[register_id] & 0x0F00) == 0xF00) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((gb->registers[register_id] & 0xFF00) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void ld_hr_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = ((opcode >> 4) + 1) & 0x03;
    gb->registers[register_id] &= 0xFF;
    gb->registers[register_id] |= cycle_read_inc_oam_bug(gb, gb->pc++) << 8;
}

static void rlca(GB_gameboy_t *gb, uint8_t opcode)
{
    bool carry = (gb->registers[GB_REGISTER_AF] & 0x8000) != 0;

    gb->registers[GB_REGISTER_AF] = (gb->registers[GB_REGISTER_AF] & 0xFF00) << 1;
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG | 0x0100;
    }
}

static void rla(GB_gameboy_t *gb, uint8_t opcode)
{
    bool bit7 = (gb->registers[GB_REGISTER_AF] & 0x8000) != 0;
    bool carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;

    gb->registers[GB_REGISTER_AF] = (gb->registers[GB_REGISTER_AF] & 0xFF00) << 1;
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= 0x0100;
    }
    if (bit7) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void ld_da16_sp(GB_gameboy_t *gb, uint8_t opcode)
{
    /* Todo: Verify order is correct */
    uint16_t addr;
    addr = cycle_read_inc_oam_bug(gb, gb->pc++);
    addr |= cycle_read_inc_oam_bug(gb, gb->pc++) << 8;
    cycle_write(gb, addr, gb->registers[GB_REGISTER_SP] & 0xFF);
    cycle_write(gb, addr+1, gb->registers[GB_REGISTER_SP] >> 8);
}

static void add_hl_rr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t hl = gb->registers[GB_REGISTER_HL];
    uint16_t rr;
    uint8_t register_id;
    cycle_no_access(gb);
    register_id = (opcode >> 4) + 1;
    rr = gb->registers[register_id];
    gb->registers[GB_REGISTER_HL] = hl + rr;
    gb->registers[GB_REGISTER_AF] &= ~(GB_SUBTRACT_FLAG | GB_CARRY_FLAG | GB_HALF_CARRY_FLAG);

    /* The meaning of the Half Carry flag is really hard to track -_- */
    if (((hl & 0xFFF) + (rr & 0xFFF)) & 0x1000) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ( ((unsigned long) hl + (unsigned long) rr) & 0x10000) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void ld_a_drr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = (opcode >> 4) + 1;
    gb->registers[GB_REGISTER_AF] &= 0xFF;
    gb->registers[GB_REGISTER_AF] |= cycle_read(gb, gb->registers[register_id]) << 8;
}

static void dec_rr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id = (opcode >> 4) + 1;
    cycle_oam_bug(gb, register_id);
    gb->registers[register_id]--;
}

static void inc_lr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    uint8_t value;
    register_id = (opcode >> 4) + 1;

    value = (gb->registers[register_id] & 0xFF) + 1;
    gb->registers[register_id] = (gb->registers[register_id] & 0xFF00) | value;

    gb->registers[GB_REGISTER_AF] &= ~(GB_SUBTRACT_FLAG | GB_ZERO_FLAG | GB_HALF_CARRY_FLAG);

    if ((gb->registers[register_id] & 0x0F) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((gb->registers[register_id] & 0xFF) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}
static void dec_lr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    uint8_t value;
    register_id = (opcode >> 4) + 1;

    value = (gb->registers[register_id] & 0xFF) - 1;
    gb->registers[register_id] = (gb->registers[register_id] & 0xFF00) | value;

    gb->registers[GB_REGISTER_AF] &= ~(GB_ZERO_FLAG | GB_HALF_CARRY_FLAG);
    gb->registers[GB_REGISTER_AF] |= GB_SUBTRACT_FLAG;

    if ((gb->registers[register_id] & 0x0F) == 0xF) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((gb->registers[register_id] & 0xFF) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void ld_lr_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = (opcode >> 4) + 1;
    gb->registers[register_id] &= 0xFF00;
    gb->registers[register_id] |= cycle_read_inc_oam_bug(gb, gb->pc++);
}

static void rrca(GB_gameboy_t *gb, uint8_t opcode)
{
    bool carry = (gb->registers[GB_REGISTER_AF] & 0x100) != 0;

    gb->registers[GB_REGISTER_AF] = (gb->registers[GB_REGISTER_AF] >> 1) & 0xFF00;
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG | 0x8000;
    }
}

static void rra(GB_gameboy_t *gb, uint8_t opcode)
{
    bool bit1 = (gb->registers[GB_REGISTER_AF] & 0x0100) != 0;
    bool carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;

    gb->registers[GB_REGISTER_AF] = (gb->registers[GB_REGISTER_AF] >> 1) & 0xFF00;
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= 0x8000;
    }
    if (bit1) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void jr_r8(GB_gameboy_t *gb, uint8_t opcode)
{
    /* Todo: Verify timing */
    gb->pc += (int8_t)cycle_read_inc_oam_bug(gb, gb->pc) + 1;
    cycle_no_access(gb);
}

static bool condition_code(GB_gameboy_t *gb, uint8_t opcode)
{
    switch ((opcode >> 3) & 0x3) {
        case 0:
            return !(gb->registers[GB_REGISTER_AF] & GB_ZERO_FLAG);
        case 1:
            return (gb->registers[GB_REGISTER_AF] & GB_ZERO_FLAG);
        case 2:
            return !(gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG);
        case 3:
            return (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG);
    }

    return false;
}

static void jr_cc_r8(GB_gameboy_t *gb, uint8_t opcode)
{
    int8_t offset = cycle_read_inc_oam_bug(gb, gb->pc++);
    if (condition_code(gb, opcode)) {
        gb->pc += offset;
        cycle_no_access(gb);
    }
}

static void daa(GB_gameboy_t *gb, uint8_t opcode)
{
    int16_t result = gb->registers[GB_REGISTER_AF] >> 8;

    gb->registers[GB_REGISTER_AF] &= ~(0xFF00 | GB_ZERO_FLAG);

    if (gb->registers[GB_REGISTER_AF] & GB_SUBTRACT_FLAG) {
        if (gb->registers[GB_REGISTER_AF] & GB_HALF_CARRY_FLAG) {
            result = (result - 0x06) & 0xFF;
        }

        if (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) {
            result -= 0x60;
        }
    }
    else {
        if ((gb->registers[GB_REGISTER_AF] & GB_HALF_CARRY_FLAG) || (result & 0x0F) > 0x09) {
            result += 0x06;
        }

        if ((gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) || result > 0x9F) {
            result += 0x60;
        }
    }

    if ((result & 0xFF) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }

    if ((result & 0x100) == 0x100) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }

    gb->registers[GB_REGISTER_AF] &= ~GB_HALF_CARRY_FLAG;
    gb->registers[GB_REGISTER_AF] |= result << 8;
}

static void cpl(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] ^= 0xFF00;
    gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG | GB_SUBTRACT_FLAG;
}

static void scf(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    gb->registers[GB_REGISTER_AF] &= ~(GB_HALF_CARRY_FLAG | GB_SUBTRACT_FLAG);
}

static void ccf(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] ^= GB_CARRY_FLAG;
    gb->registers[GB_REGISTER_AF] &= ~(GB_HALF_CARRY_FLAG | GB_SUBTRACT_FLAG);
}

static void ld_dhli_a(GB_gameboy_t *gb, uint8_t opcode)
{
    cycle_write(gb, gb->registers[GB_REGISTER_HL]++, gb->registers[GB_REGISTER_AF] >> 8);
}

static void ld_dhld_a(GB_gameboy_t *gb, uint8_t opcode)
{
    cycle_write(gb, gb->registers[GB_REGISTER_HL]--, gb->registers[GB_REGISTER_AF] >> 8);
}

static void ld_a_dhli(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] &= 0xFF;
    gb->registers[GB_REGISTER_AF] |= cycle_read_inc_oam_bug(gb, gb->registers[GB_REGISTER_HL]++) << 8;
}

static void ld_a_dhld(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] &= 0xFF;
    gb->registers[GB_REGISTER_AF] |= cycle_read_inc_oam_bug(gb, gb->registers[GB_REGISTER_HL]--) << 8;
}

static void inc_dhl(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value;
    value = cycle_read(gb, gb->registers[GB_REGISTER_HL]) + 1;
    cycle_write(gb, gb->registers[GB_REGISTER_HL], value);

    gb->registers[GB_REGISTER_AF] &= ~(GB_SUBTRACT_FLAG | GB_ZERO_FLAG | GB_HALF_CARRY_FLAG);
    if ((value & 0x0F) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((value & 0xFF) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void dec_dhl(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value;
    value = cycle_read(gb, gb->registers[GB_REGISTER_HL]) - 1;
    cycle_write(gb, gb->registers[GB_REGISTER_HL], value);

    gb->registers[GB_REGISTER_AF] &= ~( GB_ZERO_FLAG | GB_HALF_CARRY_FLAG);
    gb->registers[GB_REGISTER_AF] |= GB_SUBTRACT_FLAG;
    if ((value & 0x0F) == 0x0F) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((value & 0xFF) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void ld_dhl_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t data = cycle_read_inc_oam_bug(gb, gb->pc++);
    cycle_write(gb, gb->registers[GB_REGISTER_HL], data);
}

static uint8_t get_src_value(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t src_register_id;
    uint8_t src_low;
    src_register_id = ((opcode >> 1) + 1) & 3;
    src_low = opcode & 1;
    if (src_register_id == GB_REGISTER_AF) {
        if (src_low) {
            return gb->registers[GB_REGISTER_AF] >> 8;
        }
        return cycle_read(gb, gb->registers[GB_REGISTER_HL]);
    }
    if (src_low) {
        return gb->registers[src_register_id] & 0xFF;
    }
    return gb->registers[src_register_id] >> 8;
}

static void set_src_value(GB_gameboy_t *gb, uint8_t opcode, uint8_t value)
{
    uint8_t src_register_id;
    uint8_t src_low;
    src_register_id = ((opcode >> 1) + 1) & 3;
    src_low = opcode & 1;

    if (src_register_id == GB_REGISTER_AF) {
        if (src_low) {
            gb->registers[GB_REGISTER_AF] &= 0xFF;
            gb->registers[GB_REGISTER_AF] |= value << 8;
        }
        else {
            cycle_write(gb, gb->registers[GB_REGISTER_HL], value);
        }
    }
    else {
        if (src_low) {
            gb->registers[src_register_id] &= 0xFF00;
            gb->registers[src_register_id] |= value;
        }
        else {
            gb->registers[src_register_id] &= 0xFF;
            gb->registers[src_register_id] |= value << 8;
        }
    }
}

/* The LD r,r instruction is extremely common and extremely simple. Decoding this opcode at runtime is a significent
   performance hit, so we generate functions for every ld x,y couple (including [hl]) at compile time using macros. */

/* Todo: It's probably wise to do the same to all opcodes. */

#define LD_X_Y(x, y) \
static void ld_##x##_##y(GB_gameboy_t *gb, uint8_t opcode) \
{ \
    gb->x = gb->y;\
}

#define LD_X_DHL(x) \
static void ld_##x##_##dhl(GB_gameboy_t *gb, uint8_t opcode) \
{ \
gb->x = cycle_read(gb, gb->registers[GB_REGISTER_HL]); \
}

#define LD_DHL_Y(y) \
static void ld_##dhl##_##y(GB_gameboy_t *gb, uint8_t opcode) \
{ \
cycle_write(gb, gb->registers[GB_REGISTER_HL], gb->y); \
}

LD_X_Y(b,c) LD_X_Y(b,d) LD_X_Y(b,e) LD_X_Y(b,h) LD_X_Y(b,l)             LD_X_DHL(b) LD_X_Y(b,a)
LD_X_Y(c,b)             LD_X_Y(c,d) LD_X_Y(c,e) LD_X_Y(c,h) LD_X_Y(c,l) LD_X_DHL(c) LD_X_Y(c,a)
LD_X_Y(d,b) LD_X_Y(d,c)             LD_X_Y(d,e) LD_X_Y(d,h) LD_X_Y(d,l) LD_X_DHL(d) LD_X_Y(d,a)
LD_X_Y(e,b) LD_X_Y(e,c) LD_X_Y(e,d)             LD_X_Y(e,h) LD_X_Y(e,l) LD_X_DHL(e) LD_X_Y(e,a)
LD_X_Y(h,b) LD_X_Y(h,c) LD_X_Y(h,d) LD_X_Y(h,e)             LD_X_Y(h,l) LD_X_DHL(h) LD_X_Y(h,a)
LD_X_Y(l,b) LD_X_Y(l,c) LD_X_Y(l,d) LD_X_Y(l,e) LD_X_Y(l,h)             LD_X_DHL(l) LD_X_Y(l,a)
LD_DHL_Y(b) LD_DHL_Y(c) LD_DHL_Y(d) LD_DHL_Y(e) LD_DHL_Y(h) LD_DHL_Y(l)             LD_DHL_Y(a)
LD_X_Y(a,b) LD_X_Y(a,c) LD_X_Y(a,d) LD_X_Y(a,e) LD_X_Y(a,h) LD_X_Y(a,l) LD_X_DHL(a)


static void add_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = (a + value) << 8;
    if ((uint8_t)(a + value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) + (value & 0xF) > 0x0F) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (((unsigned long) a) + ((unsigned long) value) > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void adc_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a, carry;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;
    gb->registers[GB_REGISTER_AF] = (a + value + carry) << 8;

    if ((uint8_t)(a + value + carry) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) + (value & 0xF) + carry > 0x0F) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (((unsigned long) a) + ((unsigned long) value) + carry > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void sub_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = ((a - value) << 8) | GB_SUBTRACT_FLAG;
    if (a == value) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) < (value & 0xF)) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (a < value) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void sbc_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a, carry;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;
    gb->registers[GB_REGISTER_AF] = ((a - value - carry) << 8) | GB_SUBTRACT_FLAG;

    if ((uint8_t) (a - value - carry) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) < (value & 0xF) + carry) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (((unsigned long) a) - ((unsigned long) value) - carry > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void and_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = ((a & value) << 8) | GB_HALF_CARRY_FLAG;
    if ((a & value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void xor_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = (a ^ value) << 8;
    if ((a ^ value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void or_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = (a | value) << 8;
    if ((a | value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void cp_a_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = get_src_value(gb, opcode);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    gb->registers[GB_REGISTER_AF] |= GB_SUBTRACT_FLAG;
    if (a == value) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) < (value & 0xF)) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (a < value) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void halt(GB_gameboy_t *gb, uint8_t opcode)
{
    assert(gb->pending_cycles == 4);
    gb->pending_cycles = 0;
    GB_advance_cycles(gb, 1);
    GB_advance_cycles(gb, 1);
    GB_advance_cycles(gb, 1);
    GB_advance_cycles(gb, 1);
    
    gb->halted = true;
    /* Despite what some online documentations say, the HALT bug also happens on a CGB, in both CGB and DMG modes. */
    if (((gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F) != 0)) {
        if (gb->ime) {
            gb->halted = false;
            gb->pc--;
        }
        else {
            gb->halted = false;
            gb->halt_bug = true;
        }
    }
    gb->just_halted = true;
}

static void pop_rr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    register_id = ((opcode >> 4) + 1) & 3;
    gb->registers[register_id] = cycle_read_inc_oam_bug(gb, gb->registers[GB_REGISTER_SP]++);
    gb->registers[register_id] |= cycle_read(gb, gb->registers[GB_REGISTER_SP]++) << 8;
    gb->registers[GB_REGISTER_AF] &= 0xFFF0; // Make sure we don't set impossible flags on F! See Blargg's PUSH AF test.
}

static void jp_cc_a16(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t addr = cycle_read_inc_oam_bug(gb, gb->pc++);
    addr |= (cycle_read_inc_oam_bug(gb, gb->pc++) << 8);
    if (condition_code(gb, opcode)) {
        cycle_no_access(gb);
        gb->pc = addr;
    }
}

static void jp_a16(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t addr = cycle_read_inc_oam_bug(gb, gb->pc);
    addr |= (cycle_read_inc_oam_bug(gb, gb->pc + 1) << 8);
    cycle_no_access(gb);
    gb->pc = addr;
    
}

static void call_cc_a16(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t call_addr = gb->pc - 1;
    uint16_t addr = cycle_read_inc_oam_bug(gb, gb->pc++);
    addr |= (cycle_read_inc_oam_bug(gb, gb->pc++) << 8);
    if (condition_code(gb, opcode)) {
        cycle_oam_bug(gb, GB_REGISTER_SP);
        cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) >> 8);
        cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) & 0xFF);
        gb->pc = addr;

        GB_debugger_call_hook(gb, call_addr);
    }
}

static void push_rr(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t register_id;
    cycle_oam_bug(gb, GB_REGISTER_SP);
    register_id = ((opcode >> 4) + 1) & 3;
    cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->registers[register_id]) >> 8);
    cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->registers[register_id]) & 0xFF);
}

static void add_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = (a + value) << 8;
    if ((uint8_t) (a + value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) + (value & 0xF) > 0x0F) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (((unsigned long) a) + ((unsigned long) value) > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void adc_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a, carry;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;
    gb->registers[GB_REGISTER_AF] = (a + value + carry) << 8;

    if (gb->registers[GB_REGISTER_AF] == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) + (value & 0xF) + carry > 0x0F) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (((unsigned long) a) + ((unsigned long) value) + carry > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void sub_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = ((a - value) << 8) | GB_SUBTRACT_FLAG;
    if (a == value) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) < (value & 0xF)) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (a < value) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void sbc_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a, carry;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;
    gb->registers[GB_REGISTER_AF] = ((a - value - carry) << 8) | GB_SUBTRACT_FLAG;

    if ((uint8_t) (a - value - carry) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) < (value & 0xF) + carry) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (((unsigned long) a) - ((unsigned long) value) - carry > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void and_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = ((a & value) << 8) | GB_HALF_CARRY_FLAG;
    if ((a & value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void xor_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = (a ^ value) << 8;
    if ((a ^ value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void or_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] = (a | value) << 8;
    if ((a | value) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void cp_a_d8(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value, a;
    value = cycle_read_inc_oam_bug(gb, gb->pc++);
    a = gb->registers[GB_REGISTER_AF] >> 8;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    gb->registers[GB_REGISTER_AF] |= GB_SUBTRACT_FLAG;
    if (a == value) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
    if ((a & 0xF) < (value & 0xF)) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }
    if (a < value) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void rst(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t call_addr = gb->pc - 1;
    cycle_oam_bug(gb, GB_REGISTER_SP);
    cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) >> 8);
    cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) & 0xFF);
    gb->pc = opcode ^ 0xC7;
    GB_debugger_call_hook(gb, call_addr);
}

static void ret(GB_gameboy_t *gb, uint8_t opcode)
{
    GB_debugger_ret_hook(gb);
    gb->pc = cycle_read_inc_oam_bug(gb, gb->registers[GB_REGISTER_SP]++);
    gb->pc |= cycle_read(gb, gb->registers[GB_REGISTER_SP]++) << 8;
    cycle_no_access(gb);
}

static void reti(GB_gameboy_t *gb, uint8_t opcode)
{
    ret(gb, opcode);
    gb->ime = true;
}

static void ret_cc(GB_gameboy_t *gb, uint8_t opcode)
{
    if (condition_code(gb, opcode)) {
        cycle_no_access(gb);
        ret(gb, opcode);
    }
    else {
        cycle_no_access(gb);
    }
}

static void call_a16(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t call_addr = gb->pc - 1;
    uint16_t addr = cycle_read_inc_oam_bug(gb, gb->pc++);
    addr |= (cycle_read_inc_oam_bug(gb, gb->pc++) << 8);
    cycle_oam_bug(gb, GB_REGISTER_SP);
    cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) >> 8);
    cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) & 0xFF);
    gb->pc = addr;
    GB_debugger_call_hook(gb, call_addr);
}

static void ld_da8_a(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t temp = cycle_read_inc_oam_bug(gb, gb->pc++);
    cycle_write(gb, 0xFF00 + temp, gb->registers[GB_REGISTER_AF] >> 8);
}

static void ld_a_da8(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] &= 0xFF;
    uint8_t temp = cycle_read_inc_oam_bug(gb, gb->pc++);
    gb->registers[GB_REGISTER_AF] |= cycle_read(gb, 0xFF00 + temp) << 8;
}

static void ld_dc_a(GB_gameboy_t *gb, uint8_t opcode)
{
    cycle_write(gb, 0xFF00 + (gb->registers[GB_REGISTER_BC] & 0xFF), gb->registers[GB_REGISTER_AF] >> 8);
}

static void ld_a_dc(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_AF] &= 0xFF;
    gb->registers[GB_REGISTER_AF] |= cycle_read(gb, 0xFF00 + (gb->registers[GB_REGISTER_BC] & 0xFF)) << 8;
}

static void add_sp_r8(GB_gameboy_t *gb, uint8_t opcode)
{
    int16_t offset;
    uint16_t sp = gb->registers[GB_REGISTER_SP];
    offset = (int8_t) cycle_read_inc_oam_bug(gb, gb->pc++);
    cycle_no_access(gb);
    cycle_no_access(gb);
    gb->registers[GB_REGISTER_SP] += offset;

    gb->registers[GB_REGISTER_AF] &= 0xFF00;

    /* A new instruction, a new meaning for Half Carry! */
    if ((sp & 0xF) + (offset & 0xF) > 0xF) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((sp & 0xFF) + (offset & 0xFF) > 0xFF)  {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void jp_hl(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->pc = gb->registers[GB_REGISTER_HL];
}

static void ld_da16_a(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t addr;
    addr = cycle_read_inc_oam_bug(gb, gb->pc++);
    addr |= cycle_read_inc_oam_bug(gb, gb->pc++) << 8;
    cycle_write(gb, addr, gb->registers[GB_REGISTER_AF] >> 8);
}

static void ld_a_da16(GB_gameboy_t *gb, uint8_t opcode)
{
    uint16_t addr;
    gb->registers[GB_REGISTER_AF] &= 0xFF;
    addr = cycle_read_inc_oam_bug(gb, gb->pc++);
    addr |= cycle_read_inc_oam_bug(gb, gb->pc++) << 8 ;
    gb->registers[GB_REGISTER_AF] |= cycle_read(gb, addr) << 8;
}

static void di(GB_gameboy_t *gb, uint8_t opcode)
{
    /* DI is NOT delayed, not even on a CGB. Mooneye's di_timing-GS test fails on a CGB
       for different reasons. */
    gb->ime = false;
}

static void ei(GB_gameboy_t *gb, uint8_t opcode)
{
    /* ei is actually "disable interrupts for one instruction, then enable them". */
    if (!gb->ime && !gb->ime_toggle) {
        gb->ime_toggle = true;
    }
}

static void ld_hl_sp_r8(GB_gameboy_t *gb, uint8_t opcode)
{
    int16_t offset;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    offset = (int8_t) cycle_read_inc_oam_bug(gb, gb->pc++);
    cycle_no_access(gb);
    gb->registers[GB_REGISTER_HL] = gb->registers[GB_REGISTER_SP] + offset;

    if ((gb->registers[GB_REGISTER_SP] & 0xF) + (offset & 0xF) > 0xF) {
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
    }

    if ((gb->registers[GB_REGISTER_SP] & 0xFF)  + (offset & 0xFF) > 0xFF) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
}

static void ld_sp_hl(GB_gameboy_t *gb, uint8_t opcode)
{
    gb->registers[GB_REGISTER_SP] = gb->registers[GB_REGISTER_HL];
    cycle_no_access(gb);
}

static void rlc_r(GB_gameboy_t *gb, uint8_t opcode)
{
    bool carry;
    uint8_t value;
    value = get_src_value(gb, opcode);
    carry = (value & 0x80) != 0;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    set_src_value(gb, opcode, (value << 1) | carry);
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    if (!(value << 1)) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void rrc_r(GB_gameboy_t *gb, uint8_t opcode)
{
    bool carry;
    uint8_t value;
    value = get_src_value(gb, opcode);
    carry = (value & 0x01) != 0;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    value = (value >> 1) | (carry << 7);
    set_src_value(gb, opcode, value);
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    if (value == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void rl_r(GB_gameboy_t *gb, uint8_t opcode)
{
    bool carry;
    uint8_t value;
    bool bit7;
    value = get_src_value(gb, opcode);
    carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;
    bit7 = (value & 0x80) != 0;

    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    value = (value << 1) | carry;
    set_src_value(gb, opcode, value);
    if (bit7) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    if (value == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void rr_r(GB_gameboy_t *gb, uint8_t opcode)
{
    bool carry;
    uint8_t value;
    bool bit1;

    value = get_src_value(gb, opcode);
    carry = (gb->registers[GB_REGISTER_AF] & GB_CARRY_FLAG) != 0;
    bit1 = (value & 0x1) != 0;

    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    value = (value >> 1) | (carry << 7);
    set_src_value(gb, opcode, value);
    if (bit1) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    if (value == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void sla_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value;
    bool carry;
    value = get_src_value(gb, opcode);
    carry = (value & 0x80) != 0;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    set_src_value(gb, opcode, (value << 1));
    if (carry) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    if ((value & 0x7F) == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void sra_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t bit7;
    uint8_t value;
    value = get_src_value(gb, opcode);
    bit7 = value & 0x80;
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    if (value & 1) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    value = (value >> 1) | bit7;
    set_src_value(gb, opcode, value);
    if (value == 0) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void srl_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value;
    value = get_src_value(gb, opcode);
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    set_src_value(gb, opcode, (value >> 1));
    if (value & 1) {
        gb->registers[GB_REGISTER_AF] |= GB_CARRY_FLAG;
    }
    if (!(value >> 1)) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void swap_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value;
    value = get_src_value(gb, opcode);
    gb->registers[GB_REGISTER_AF] &= 0xFF00;
    set_src_value(gb, opcode, (value >> 4) | (value << 4));
    if (!value) {
        gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
    }
}

static void bit_r(GB_gameboy_t *gb, uint8_t opcode)
{
    uint8_t value;
    uint8_t bit;
    value = get_src_value(gb, opcode);
    bit = 1 << ((opcode >> 3) & 7);
    if ((opcode & 0xC0) == 0x40) { /* Bit */
        gb->registers[GB_REGISTER_AF] &= 0xFF00 | GB_CARRY_FLAG;
        gb->registers[GB_REGISTER_AF] |= GB_HALF_CARRY_FLAG;
        if (!(bit & value)) {
            gb->registers[GB_REGISTER_AF] |= GB_ZERO_FLAG;
        }
    }
    else if ((opcode & 0xC0) == 0x80) { /* res */
        set_src_value(gb, opcode, value & ~bit) ;
    }
    else if ((opcode & 0xC0) == 0xC0) { /* set */
        set_src_value(gb, opcode, value | bit) ;
    }
}

static void cb_prefix(GB_gameboy_t *gb, uint8_t opcode)
{
    opcode = cycle_read_inc_oam_bug(gb, gb->pc++);
    switch (opcode >> 3) {
        case 0:
            rlc_r(gb, opcode);
            break;
        case 1:
            rrc_r(gb, opcode);
            break;
        case 2:
            rl_r(gb, opcode);
            break;
        case 3:
            rr_r(gb, opcode);
            break;
        case 4:
            sla_r(gb, opcode);
            break;
        case 5:
            sra_r(gb, opcode);
            break;
        case 6:
            swap_r(gb, opcode);
            break;
        case 7:
            srl_r(gb, opcode);
            break;
        default:
            bit_r(gb, opcode);
            break;
    }
}

static GB_opcode_t *opcodes[256] = {
    /*  X0          X1          X2          X3          X4          X5          X6          X7                */
    /*  X8          X9          Xa          Xb          Xc          Xd          Xe          Xf                */
    nop,        ld_rr_d16,  ld_drr_a,   inc_rr,     inc_hr,     dec_hr,     ld_hr_d8,   rlca,       /* 0X */
    ld_da16_sp, add_hl_rr,  ld_a_drr,   dec_rr,     inc_lr,     dec_lr,     ld_lr_d8,   rrca,
    stop,       ld_rr_d16,  ld_drr_a,   inc_rr,     inc_hr,     dec_hr,     ld_hr_d8,   rla,        /* 1X */
    jr_r8,      add_hl_rr,  ld_a_drr,   dec_rr,     inc_lr,     dec_lr,     ld_lr_d8,   rra,
    jr_cc_r8,   ld_rr_d16,  ld_dhli_a,  inc_rr,     inc_hr,     dec_hr,     ld_hr_d8,   daa,        /* 2X */
    jr_cc_r8,   add_hl_rr,  ld_a_dhli,  dec_rr,     inc_lr,     dec_lr,     ld_lr_d8,   cpl,
    jr_cc_r8,   ld_rr_d16,  ld_dhld_a,  inc_rr,     inc_dhl,    dec_dhl,    ld_dhl_d8,  scf,        /* 3X */
    jr_cc_r8,   add_hl_rr,  ld_a_dhld,  dec_rr,     inc_hr,     dec_hr,     ld_hr_d8,   ccf,
    nop,        ld_b_c,     ld_b_d,     ld_b_e,     ld_b_h,     ld_b_l,     ld_b_dhl,   ld_b_a,     /* 4X */
    ld_c_b,     nop,        ld_c_d,     ld_c_e,     ld_c_h,     ld_c_l,     ld_c_dhl,   ld_c_a,
    ld_d_b,     ld_d_c,     nop,        ld_d_e,     ld_d_h,     ld_d_l,     ld_d_dhl,   ld_d_a,     /* 5X */
    ld_e_b,     ld_e_c,     ld_e_d,     nop,        ld_e_h,     ld_e_l,     ld_e_dhl,   ld_e_a,
    ld_h_b,     ld_h_c,     ld_h_d,     ld_h_e,     nop,        ld_h_l,     ld_h_dhl,   ld_h_a,     /* 6X */
    ld_l_b,     ld_l_c,     ld_l_d,     ld_l_e,     ld_l_h,     nop,        ld_l_dhl,   ld_l_a,
    ld_dhl_b,   ld_dhl_c,   ld_dhl_d,   ld_dhl_e,   ld_dhl_h,   ld_dhl_l,   halt,       ld_dhl_a,   /* 7X */
    ld_a_b,     ld_a_c,     ld_a_d,     ld_a_e,     ld_a_h,     ld_a_l,     ld_a_dhl,   nop,
    add_a_r,    add_a_r,    add_a_r,    add_a_r,    add_a_r,    add_a_r,    add_a_r,    add_a_r,    /* 8X */
    adc_a_r,    adc_a_r,    adc_a_r,    adc_a_r,    adc_a_r,    adc_a_r,    adc_a_r,    adc_a_r,
    sub_a_r,    sub_a_r,    sub_a_r,    sub_a_r,    sub_a_r,    sub_a_r,    sub_a_r,    sub_a_r,    /* 9X */
    sbc_a_r,    sbc_a_r,    sbc_a_r,    sbc_a_r,    sbc_a_r,    sbc_a_r,    sbc_a_r,    sbc_a_r,
    and_a_r,    and_a_r,    and_a_r,    and_a_r,    and_a_r,    and_a_r,    and_a_r,    and_a_r,    /* aX */
    xor_a_r,    xor_a_r,    xor_a_r,    xor_a_r,    xor_a_r,    xor_a_r,    xor_a_r,    xor_a_r,
    or_a_r,     or_a_r,     or_a_r,     or_a_r,     or_a_r,     or_a_r,     or_a_r,     or_a_r,     /* bX */
    cp_a_r,     cp_a_r,     cp_a_r,     cp_a_r,     cp_a_r,     cp_a_r,     cp_a_r,     cp_a_r,
    ret_cc,     pop_rr,     jp_cc_a16,  jp_a16,     call_cc_a16,push_rr,    add_a_d8,   rst,        /* cX */
    ret_cc,     ret,        jp_cc_a16,  cb_prefix,  call_cc_a16,call_a16,   adc_a_d8,   rst,
    ret_cc,     pop_rr,     jp_cc_a16,  ill,        call_cc_a16,push_rr,    sub_a_d8,   rst,        /* dX */
    ret_cc,     reti,       jp_cc_a16,  ill,        call_cc_a16,ill,        sbc_a_d8,   rst,
    ld_da8_a,   pop_rr,     ld_dc_a,    ill,        ill,        push_rr,    and_a_d8,   rst,        /* eX */
    add_sp_r8,  jp_hl,      ld_da16_a,  ill,        ill,        ill,        xor_a_d8,   rst,
    ld_a_da8,   pop_rr,     ld_a_dc,    di,         ill,        push_rr,    or_a_d8,    rst,        /* fX */
    ld_hl_sp_r8,ld_sp_hl,   ld_a_da16,  ei,         ill,        ill,        cp_a_d8,    rst,
};
void GB_cpu_run(GB_gameboy_t *gb)
{
    if (gb->hdma_on) {
        GB_advance_cycles(gb, 4);
        return;
    }
    if (gb->stopped) {
        GB_timing_sync(gb);
        GB_advance_cycles(gb, 4);
        if ((gb->io_registers[GB_IO_JOYP] & 0xF) != 0xF) {
            leave_stop_mode(gb);
            GB_advance_cycles(gb, 8);
        }
        return;
    }
    
    if ((gb->interrupt_enable & 0x10) && (gb->ime || gb->halted)) {
        GB_timing_sync(gb);
    }
    
    if (gb->halted && !GB_is_cgb(gb) && !gb->just_halted) {
        GB_advance_cycles(gb, 2);
    }
    
    uint8_t interrupt_queue = gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F;
    
    if (gb->halted) {
        GB_advance_cycles(gb, (GB_is_cgb(gb) || gb->just_halted) ? 4 : 2);
    }
    gb->just_halted = false;

    bool effective_ime = gb->ime;
    if (gb->ime_toggle) {
        gb->ime = !gb->ime;
        gb->ime_toggle = false;
    }

    /* Wake up from HALT mode without calling interrupt code. */
    if (gb->halted && !effective_ime && interrupt_queue) {
        gb->halted = false;
    }
    
    /* Call interrupt */
    else if (effective_ime && interrupt_queue) {
        gb->halted = false;
        uint16_t call_addr = gb->pc;
        
        cycle_no_access(gb);
        cycle_no_access(gb);
        GB_trigger_oam_bug(gb, gb->registers[GB_REGISTER_SP]); /* Todo: test T-cycle timing */
        cycle_no_access(gb);
        
        cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) >> 8);
        interrupt_queue = gb->interrupt_enable;
        
        if (gb->registers[GB_REGISTER_SP] == GB_IO_IF + 0xFF00 + 1) {
            gb->registers[GB_REGISTER_SP]--;
            interrupt_queue &= cycle_write_if(gb, (gb->pc) & 0xFF);
        }
        else {
            cycle_write(gb, --gb->registers[GB_REGISTER_SP], (gb->pc) & 0xFF);
            interrupt_queue &= (gb->io_registers[GB_IO_IF]) & 0x1F;
        }
        
        if (interrupt_queue) {
            uint8_t interrupt_bit = 0;
            while (!(interrupt_queue & 1)) {
                interrupt_queue >>= 1;
                interrupt_bit++;
            }
            gb->io_registers[GB_IO_IF] &= ~(1 << interrupt_bit);
            gb->pc = interrupt_bit * 8 + 0x40;
        }
        else {
            gb->pc = 0;
        }
        gb->ime = false;
        GB_debugger_call_hook(gb, call_addr);
    }
    /* Run mode */
    else if(!gb->halted) {
        gb->last_opcode_read = cycle_read_inc_oam_bug(gb, gb->pc++);
        if (gb->halt_bug) {
            gb->pc--;
            gb->halt_bug = false;
        }
        opcodes[gb->last_opcode_read](gb, gb->last_opcode_read);
    }
    
    flush_pending_cycles(gb);

    if (gb->hdma_starting) {
        gb->hdma_starting = false;
        gb->hdma_on = true;
        gb->hdma_cycles = -8;
    }
}