clem_code.h

#include "clem_mem.h"
#include "clem_types.h"

//  inlined header
#include "clem_cycle.h"

static inline void _cpu_p_flags_n_data(struct Clemens65C816 *cpu, uint8_t data) {
    if (data & 0x80) {
        cpu->regs.P |= kClemensCPUStatus_Negative;
    } else {
        cpu->regs.P &= ~kClemensCPUStatus_Negative;
    }
}

static inline void _cpu_p_flags_n_data_16(struct Clemens65C816 *cpu, uint16_t data) {
    if (data & 0x8000) {
        cpu->regs.P |= kClemensCPUStatus_Negative;
    } else {
        cpu->regs.P &= ~kClemensCPUStatus_Negative;
    }
}

static inline void _cpu_p_flags_z_data(struct Clemens65C816 *cpu, uint8_t data) {
    if (data) {
        cpu->regs.P &= ~kClemensCPUStatus_Zero;
    } else {
        cpu->regs.P |= kClemensCPUStatus_Zero;
    }
}

static inline void _cpu_p_flags_z_data_16(struct Clemens65C816 *cpu, uint16_t data) {
    if (data) {
        cpu->regs.P &= ~kClemensCPUStatus_Zero;
    } else {
        cpu->regs.P |= kClemensCPUStatus_Zero;
    }
}

static inline void _cpu_p_flags_n_z_data(struct Clemens65C816 *cpu, uint8_t data) {
    _cpu_p_flags_n_data(cpu, data);
    _cpu_p_flags_z_data(cpu, data);
}

static inline void _cpu_p_flags_n_z_data_16(struct Clemens65C816 *cpu, uint16_t data) {
    _cpu_p_flags_n_data_16(cpu, data);
    _cpu_p_flags_z_data_16(cpu, data);
}

static inline void _cpu_p_flags_n_z_data_816(struct Clemens65C816 *cpu, uint16_t data, bool is8) {
    if (is8) {
        _cpu_p_flags_n_z_data(cpu, (uint8_t)data);
    } else {
        _cpu_p_flags_n_z_data_16(cpu, data);
    }
}

static inline void _cpu_p_flags_apply_m_x(struct Clemens65C816 *cpu) {
    bool idx8 = (cpu->regs.P & kClemensCPUStatus_Index) != 0;
    if (idx8) {
        cpu->regs.X &= 0xff;
        cpu->regs.Y &= 0xff;
    } else {
        cpu->regs.P &= ~kClemensCPUStatus_Index;
    }
}

static inline void _cpu_sp_dec3(struct Clemens65C816 *cpu) {
    uint16_t tmp = cpu->regs.S - 3;
    if (cpu->pins.emulation) {
        tmp = (cpu->regs.S & 0xff00) | (tmp & 0x00ff);
    }
    cpu->regs.S = tmp;
}

static inline void _cpu_sp_dec2(struct Clemens65C816 *cpu) {
    uint16_t tmp = cpu->regs.S - 2;
    if (cpu->pins.emulation) {
        tmp = (cpu->regs.S & 0xff00) | (tmp & 0x00ff);
    }
    cpu->regs.S = tmp;
}

static inline void _cpu_sp_dec(struct Clemens65C816 *cpu) {
    uint16_t tmp = cpu->regs.S - 1;
    if (cpu->pins.emulation) {
        tmp = (cpu->regs.S & 0xff00) | (tmp & 0x00ff);
    }
    cpu->regs.S = tmp;
}

static inline void _cpu_sp_inc3(struct Clemens65C816 *cpu) {
    uint16_t tmp = cpu->regs.S + 3;
    if (cpu->pins.emulation) {
        tmp = (cpu->regs.S & 0xff00) | (tmp & 0x00ff);
    }
    cpu->regs.S = tmp;
}

static inline void _cpu_sp_inc2(struct Clemens65C816 *cpu) {
    uint16_t tmp = cpu->regs.S + 2;
    if (cpu->pins.emulation) {
        tmp = (cpu->regs.S & 0xff00) | (tmp & 0x00ff);
    }
    cpu->regs.S = tmp;
}

static inline void _cpu_sp_inc(struct Clemens65C816 *cpu) {
    uint16_t tmp = cpu->regs.S + 1;
    if (cpu->pins.emulation) {
        tmp = (cpu->regs.S & 0xff00) | (tmp & 0x00ff);
    }
    cpu->regs.S = tmp;
}

/*  Memory Reads and Writes:
    Requirements:
        Handle FPI access to ROM
        Handle FPI and MEGA2 fast and slow accesses to RAM
        Handle Access based on the Shadow Register
*/
static inline void _clem_io_read_cycle(ClemensMachine *clem, uint16_t addr, uint16_t idx,
                                       uint8_t bank) {
    /* special rules for IO cycles called out here but decision to call
       determined by the caller (to minimize conditional logic)
       x = 0, crossing page boundaries on index, or write
    */
    uint8_t offset = (uint8_t)(addr & 0xff);
    uint8_t tmp_data;
    // read from DBR,AAH.AAL+YL per WDC 65816 spec
    addr = (addr & 0xff00) | (uint8_t)(offset + (idx & 0xff));
    clem_read(clem, &tmp_data, addr, bank, CLEM_MEM_FLAG_BUS_IO);
}

static inline void _clem_next_dbr(ClemensMachine *clem, uint8_t *next_dbr, uint8_t dbr) {
    if (!clem->cpu.pins.emulation) {
        *next_dbr = dbr + 1;
    } else {
        *next_dbr = dbr;
    }
}

static inline void _clem_write_16(ClemensMachine *clem, uint16_t data, uint16_t adr, uint8_t bank) {
    uint16_t adr_1 = adr + 1;
    uint16_t bank_1 = adr_1 ? bank : bank + 1;
    clem_write(clem, (uint8_t)data, adr, bank, CLEM_MEM_FLAG_DATA);
    clem_write(clem, (uint8_t)(data >> 8), adr_1, bank_1, CLEM_MEM_FLAG_DATA);
}

static inline void _clem_write_16_wrap(ClemensMachine *clem, uint16_t data, uint16_t adr, uint8_t bank) {
    clem_write(clem, (uint8_t)data, adr, bank, CLEM_MEM_FLAG_DATA);
    clem_write(clem, (uint8_t)(data >> 8), adr + 1, bank, CLEM_MEM_FLAG_DATA);
}

static inline void _clem_read_16(ClemensMachine *clem, uint16_t *data16, uint16_t adr, uint8_t bank,
                                 uint8_t flags) {
    uint16_t adr_1 = adr + 1;
    uint16_t bank_1 = adr_1 ? bank : bank + 1;
    uint8_t tmp_data;
    clem_read(clem, &tmp_data, adr, bank, flags);
    *data16 = tmp_data;
    clem_read(clem, &tmp_data, adr_1, bank_1, flags);
    *data16 = ((uint16_t)tmp_data << 8) | (*data16);
}

static inline void _clem_read_16_wrap(ClemensMachine *clem, uint16_t *data16, uint16_t adr, uint8_t bank,
                                 uint8_t flags) {
    uint8_t tmp_data;
    clem_read(clem, &tmp_data, adr, bank, flags);
    *data16 = tmp_data;
    clem_read(clem, &tmp_data, adr + 1, bank, flags);
    *data16 = ((uint16_t)tmp_data << 8) | (*data16);
}

static inline void _clem_read_pba(ClemensMachine *clem, uint8_t *data, uint16_t *pc) {
    clem_read(clem, data, (*pc)++, clem->cpu.regs.PBR, CLEM_MEM_FLAG_PROGRAM);
}

static inline void _clem_read_pba_16(ClemensMachine *clem, uint16_t *data16, uint16_t *pc) {
    uint8_t tmp_data;
    _clem_read_pba(clem, &tmp_data, pc);
    *data16 = tmp_data;
    _clem_read_pba(clem, &tmp_data, pc);
    *data16 = ((uint16_t)tmp_data << 8) | (*data16);
}

static inline void _clem_read_pba_816(ClemensMachine *clem, uint16_t *out, uint16_t *pc, bool is8) {
    uint8_t tmp_data;
    _clem_read_pba(clem, &tmp_data, pc);
    *out = tmp_data;
    if (!is8) {
        _clem_read_pba(clem, &tmp_data, pc);
        *out = ((uint16_t)tmp_data << 8) | *out;
    }
}
                        
static inline void _clem_read_data_816(ClemensMachine *clem, uint16_t *out, uint16_t addr,
                                       uint8_t dbr, bool is8) {
    uint8_t tmp_data;
    clem_read(clem, &tmp_data, addr, dbr, CLEM_MEM_FLAG_DATA);
    *out = tmp_data;
    if (!is8) {
        uint8_t next_dbr;
        ++addr;
        if (!addr) {
            _clem_next_dbr(clem, &next_dbr, dbr);
        } else {
            next_dbr = dbr;
        }
        clem_read(clem, &tmp_data, addr, next_dbr, CLEM_MEM_FLAG_DATA);
        *out = ((uint16_t)tmp_data << 8) | *out;
    }
}

static inline void _clem_read_data_indexed_816(ClemensMachine *clem, uint16_t *out, uint16_t addr,
                                               uint16_t index, uint8_t dbr, bool is_data_8,
                                               bool is_index_8) {
    uint8_t dbr_actual;
    uint16_t eff_index = is_index_8 ? (index & 0xff) : index;
    uint16_t eff_addr = addr + eff_index;
    if (eff_addr < addr && !clem->cpu.pins.emulation) {
        _clem_next_dbr(clem, &dbr_actual, dbr);
    } else {
        dbr_actual = dbr;
    }
    if (!is_index_8 || CLEM_UTIL_CROSSED_PAGE_BOUNDARY(addr, eff_addr)) {
        //  indexed address crossing a page boundary adds a cycle
        _clem_cycle(clem);
    }
    _clem_read_data_816(clem, out, eff_addr, dbr_actual, is_data_8);
}

static inline void _clem_opc_push_reg_816(ClemensMachine *clem, uint16_t data, bool is8) {
    struct Clemens65C816 *cpu = &clem->cpu;
    _clem_cycle(clem);
    if (!is8) {
        clem_write(clem, (uint8_t)(data >> 8), cpu->regs.S, 0x00, CLEM_MEM_FLAG_DATA);
        _cpu_sp_dec(cpu);
    }
    clem_write(clem, (uint8_t)(data), cpu->regs.S, 0x00, CLEM_MEM_FLAG_DATA);
    _cpu_sp_dec(cpu);
}

static inline void _clem_opc_push_reg_8(ClemensMachine *clem, uint8_t data) {
    struct Clemens65C816 *cpu = &clem->cpu;
    _clem_cycle(clem);
    clem_write(clem, data, cpu->regs.S, 0x00, CLEM_MEM_FLAG_DATA);
    _cpu_sp_dec(cpu);
}

static inline void _clem_opc_pull_reg_816(ClemensMachine *clem, uint16_t *data, bool is8) {
    struct Clemens65C816 *cpu = &clem->cpu;
    uint8_t data8;
    _clem_cycle_2(clem);
    _cpu_sp_inc(cpu);
    clem_read(clem, &data8, cpu->regs.S, 0x00, CLEM_MEM_FLAG_DATA);
    *data = CLEM_UTIL_set16_lo(*data, data8);
    if (!is8) {
        _cpu_sp_inc(cpu);
        clem_read(clem, &data8, cpu->regs.S, 0x00, CLEM_MEM_FLAG_DATA);
        *data = CLEM_UTIL_set16_lo((uint16_t)(data8) << 8, *data);
    }
}

static inline void _clem_opc_pull_reg_8(ClemensMachine *clem, uint8_t *data) {
    struct Clemens65C816 *cpu = &clem->cpu;
    _clem_cycle_2(clem);
    _cpu_sp_inc(cpu);
    clem_read(clem, data, cpu->regs.S, 0x00, CLEM_MEM_FLAG_DATA);
}

static inline void _clem_opc_push_status(ClemensMachine *clem, bool is_irq) {
    uint8_t tmp_p = clem->cpu.regs.P;
    if (clem->cpu.pins.emulation) {
        if (is_irq) {
            tmp_p &= ~kClemensCPUStatus_EmulatedBrk;
        } else {
            tmp_p |= kClemensCPUStatus_Index;
        }
        tmp_p |= kClemensCPUStatus_MemoryAccumulator;
    }
    clem_write(clem, tmp_p, clem->cpu.regs.S, 0x00, CLEM_MEM_FLAG_DATA);
    _cpu_sp_dec(&clem->cpu);
}

static inline void _clem_opc_pull_status(ClemensMachine *clem) {
    uint8_t tmp_p;
    _cpu_sp_inc(&clem->cpu);
    clem_read(clem, &tmp_p, clem->cpu.regs.S, 0x00, CLEM_MEM_FLAG_DATA);

    if (clem->cpu.pins.emulation) {
        tmp_p |= kClemensCPUStatus_MemoryAccumulator;
        tmp_p |= kClemensCPUStatus_Index;
    }
    clem->cpu.regs.P = tmp_p;
    _cpu_p_flags_apply_m_x(&clem->cpu);
}

static inline void _clem_opc_push_pc16(ClemensMachine *clem, uint16_t pc) {
    uint16_t tmp_s = clem->cpu.regs.S;
    //  stack receives last address of operand
    clem_write(clem, (uint8_t)(pc >> 8), tmp_s, 0x00, CLEM_MEM_FLAG_DATA);
    --tmp_s;
    if (clem->cpu.pins.emulation) {
        tmp_s = CLEM_UTIL_set16_lo(clem->cpu.regs.S, tmp_s);
    }
    clem_write(clem, (uint8_t)pc, tmp_s, 0x00, CLEM_MEM_FLAG_DATA);
    _cpu_sp_dec2(&clem->cpu);
}

/*  Handle opcode addressing modes
 */
static inline void _clem_read_pba_mode_imm_816(ClemensMachine *clem, uint16_t *imm, uint16_t *pc,
                                               bool is8) {
    _clem_read_pba_816(clem, imm, pc, is8);
}

static inline void _clem_read_pba_mode_abs(ClemensMachine *clem, uint16_t *addr, uint16_t *pc) {
    _clem_read_pba_16(clem, addr, pc);
}

static inline void _clem_read_pba_mode_absl(ClemensMachine *clem, uint16_t *addr, uint8_t *dbr,
                                            uint16_t *pc) {
    _clem_read_pba_16(clem, addr, pc);
    _clem_read_pba(clem, dbr, pc);
}

static inline void _clem_read_pba_mode_dp(ClemensMachine *clem, uint16_t *eff_addr, uint16_t *pc,
                                          uint8_t *offset, uint16_t index, bool is_index_8) {
    uint16_t D = clem->cpu.regs.D;
    uint16_t offset_index = is_index_8 ? (index & 0xff) : index;

    _clem_read_pba(clem, offset, pc);
    offset_index += *offset;
    if (clem->cpu.pins.emulation && !(D & 0xff)) {  // page boundary wrap?
        *eff_addr = (D & 0xff00) + ((D & 0xff) + offset_index) % 256;
    } else {
        *eff_addr = D + offset_index;
    }
    if (D & 0x00ff) {
        _clem_cycle(clem);
    }
}

static inline void _clem_read_pba_mode_dp_indirect(ClemensMachine *clem, uint16_t *eff_addr,
                                                   uint16_t *pc, uint8_t *offset, uint16_t index,
                                                   bool is_index_8) {
    uint16_t tmp_addr;
    _clem_read_pba_mode_dp(clem, &tmp_addr, pc, offset, index, is_index_8);
    _clem_read_16(clem, eff_addr, tmp_addr, 0x00, CLEM_MEM_FLAG_DATA);
}

static inline void _clem_read_pba_mode_dp_indirectl(ClemensMachine *clem, uint16_t *eff_addr,
                                                    uint8_t *eff_bank, uint16_t *pc,
                                                    uint8_t *offset, uint16_t index,
                                                    bool is_index_8) {
    /* read address located in direct page offset: lo, hi, bank ->
       eff_addr, eff_bank)
    */
    uint16_t tmp_addr;
    _clem_read_pba_mode_dp(clem, &tmp_addr, pc, offset, index, is_index_8);
    _clem_read_16(clem, eff_addr, tmp_addr, 0x00, CLEM_MEM_FLAG_DATA);
    //  TODO: direct page wrap? (DH, DL=255 + 1 = DH, 0)?
    clem_read(clem, eff_bank, tmp_addr + 2, 0x00, CLEM_MEM_FLAG_DATA);
}

static inline void _clem_read_pba_mode_stack_rel(ClemensMachine *clem, uint16_t *addr, uint16_t *pc,
                                                 uint8_t *offset) {
    _clem_read_pba(clem, offset, pc);
    _clem_cycle(clem); //  extra IO
    *addr = clem->cpu.regs.S + *offset;
}

static inline void _clem_read_pba_mode_stack_rel_indirect(ClemensMachine *clem, uint16_t *addr,
                                                          uint16_t *pc, uint8_t *offset) {
    uint16_t tmp_addr;
    _clem_read_pba_mode_stack_rel(clem, &tmp_addr, pc, offset);
    _clem_read_16(clem, addr, tmp_addr, 0x00, CLEM_MEM_FLAG_DATA);
    _clem_cycle(clem); //  extra IO
}

static inline void _cpu_adc(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    uint32_t adc;
    uint8_t p;
    bool carry = (cpu->regs.P & kClemensCPUStatus_Carry) != 0;
    if (is8) {
        value = value & 0xff;
        adc = (cpu->regs.A & 0xff) + value + carry;
        _cpu_p_flags_n_z_data(cpu, (uint8_t)adc);
        p = cpu->regs.P;
        if (((cpu->regs.A & 0xff) ^ adc) & (value ^ adc) & 0x80)
            p |= kClemensCPUStatus_Overflow;
        else
            p &= ~kClemensCPUStatus_Overflow;
        if (adc & 0x100)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, adc);
    } else {
        adc = cpu->regs.A + value + carry;
        _cpu_p_flags_n_z_data_16(cpu, (uint16_t)adc);
        p = cpu->regs.P;
        if ((cpu->regs.A ^ adc) & (value ^ adc) & 0x8000)
            p |= kClemensCPUStatus_Overflow;
        else
            p &= ~kClemensCPUStatus_Overflow;
        if (adc & 0x10000)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.A = (uint16_t)adc;
    }
    cpu->regs.P = p;
}

static inline void _cpu_adc_bcd(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    /* note, invalid BCD should still function according to specific rules. see
       https://math.stackexchange.com/questions/945320/why-do-we-add-6-in-bcd-addition
    */
    uint32_t adc;
    uint8_t p;
    bool carry = (cpu->regs.P & kClemensCPUStatus_Carry) != 0;
    if (is8) {
        value = value & 0xff;
        adc = (cpu->regs.A & 0x0f) + (value & 0x0f) + carry;
        if (adc > 0x09)
            adc += 0x06;
        carry = adc > 0x0f;
        adc = (cpu->regs.A & 0xf0) + (value & 0xf0) + (carry << 4) + (adc & 0x0f);
        p = cpu->regs.P;
        if (((cpu->regs.A & 0xff) ^ adc) & (value ^ adc) & 0x80)
            p |= kClemensCPUStatus_Overflow;
        else
            p &= ~kClemensCPUStatus_Overflow;
        if (adc > 0x9f)
            adc += 0x60;
        _cpu_p_flags_n_z_data(cpu, (uint8_t)adc);
        p = cpu->regs.P;
        if (adc & 0x100)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, adc);
    } else {
        adc = (cpu->regs.A & 0x0f) + (value & 0x0f) + carry;
        if (adc > 0x09)
            adc += 0x06;
        carry = adc > 0x0f;
        adc = (cpu->regs.A & 0xf0) + (value & 0xf0) + (carry << 4) + (adc & 0x0f);
        if (adc > 0x9f)
            adc += 0x60;
        carry = adc > 0xff;
        adc = (cpu->regs.A & 0xf00) + (value & 0xf00) + (carry << 8) + (adc & 0xff);
        if (adc > 0x9ff)
            adc += 0x600;
        carry = adc > 0xfff;
        adc = (cpu->regs.A & 0xf000) + (value & 0xf000) + (carry << 12) + (adc & 0xfff);
        p = cpu->regs.P;
        if ((cpu->regs.A ^ adc) & (value ^ adc) & 0x8000)
            p |= kClemensCPUStatus_Overflow;
        else
            p &= ~kClemensCPUStatus_Overflow;
        if (adc > 0x9fff)
            adc += 0x6000;
        _cpu_p_flags_n_z_data_16(cpu, (uint16_t)adc);
        p = cpu->regs.P;
        if (adc & 0x10000)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.A = (uint16_t)adc;
    }
    cpu->regs.P = p;
}

static inline void _cpu_sbc(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    /* inverse adc implementation a + (-b) */
    uint32_t adc;
    uint8_t p;
    bool carry = (cpu->regs.P & kClemensCPUStatus_Carry) != 0;
    if (is8) {
        uint16_t a = cpu->regs.A & 0xff;
        value = value & 0xff;
        value = value ^ 0xff; // convert to negative
        adc = a + value + carry;
        _cpu_p_flags_n_z_data(cpu, (uint8_t)adc);
        p = cpu->regs.P;
        if ((a ^ adc) & (value ^ adc) & 0x80)
            p |= kClemensCPUStatus_Overflow;
        else
            p &= ~kClemensCPUStatus_Overflow;
        if (adc & 0x100)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, adc);
    } else {
        value = value ^ 0xffff; // negative
        adc = cpu->regs.A + value + carry;
        _cpu_p_flags_n_z_data_16(cpu, (uint16_t)adc);
        p = cpu->regs.P;
        if ((cpu->regs.A ^ adc) & (value ^ adc) & 0x8000)
            p |= kClemensCPUStatus_Overflow;
        else
            p &= ~kClemensCPUStatus_Overflow;
        if (adc & 0x10000)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.A = (uint16_t)adc;
    }
    cpu->regs.P = p;
}

static inline void _cpu_sbc_bcd(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    /* note, invalid BCD should still function according to specific rules. see
       https://math.stackexchange.com/questions/945320/why-do-we-add-6-in-bcd-addition
    */
    uint32_t a_tmp;
    uint32_t sbc;
    uint32_t sbc_2comp;
    uint8_t p;
    bool carry = (cpu->regs.P & kClemensCPUStatus_Carry) != 0;
    if (is8) {
        a_tmp = (cpu->regs.A & 0x00ff);
        value = value & 0xff;
        sbc = (a_tmp & 0x0f) - (value & 0x0f) - !carry;
        if (sbc & 0x10) {
            /* borrow */
            sbc = (sbc - 0x06) & 0x0f;
            sbc |= ((a_tmp & 0xf0) - (value & 0xf0) - 0x10);
        } else {
            sbc = (sbc & 0x0f);
            sbc |= ((a_tmp & 0xf0) - (value & 0xf0));
        }
        if (sbc & 0x100)
            sbc -= 0x60;
        sbc_2comp = a_tmp - value - !carry;
        carry = (sbc_2comp < 0x100);
        _cpu_p_flags_n_z_data(cpu, (uint8_t)(sbc_2comp & 0xff));
        p = cpu->regs.P;
        if (((a_tmp ^ sbc_2comp) & 0x80) && ((a_tmp ^ value) & 0x80)) {
            p |= kClemensCPUStatus_Overflow;
        } else {
            p &= ~kClemensCPUStatus_Overflow;
        }
        if (carry) {
            p |= kClemensCPUStatus_Carry;
        } else {
            p &= ~kClemensCPUStatus_Carry;
        }
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, (uint16_t)(sbc & 0xff));
    } else {
        a_tmp = cpu->regs.A;
        sbc = (a_tmp & 0x0f) - (value & 0x0f) - !carry;
        if (sbc & 0x10) {
            /* borrow */
            sbc = (sbc - 0x06) & 0x0f;
            sbc |= ((a_tmp & 0xf0) - (value & 0xf0) - 0x10);
        } else {
            sbc = (sbc & 0x0f);
            sbc |= ((a_tmp & 0xf0) - (value & 0xf0));
        }
        if (sbc & 0x100) {
            sbc = (sbc - 0x60) & 0xff;
            sbc |= ((a_tmp & 0xf00) - (value & 0xf00) - 0x100);
        } else {
            sbc = (sbc & 0xff);
            sbc |= ((a_tmp & 0xf00) - (value & 0xf00));
        }
        if (sbc & 0x1000)
            sbc -= 0x600;
        sbc_2comp = a_tmp - value - !carry;
        carry = (sbc_2comp < 0x10000);
        _cpu_p_flags_n_z_data_16(cpu, (uint16_t)sbc_2comp);
        p = cpu->regs.P;
        if (((a_tmp ^ sbc) & 0x8000) && ((a_tmp ^ value) & 0x8000)) {
            p |= kClemensCPUStatus_Overflow;
        } else {
            p &= ~kClemensCPUStatus_Overflow;
        }
        if (carry) {
            p |= kClemensCPUStatus_Carry;
        } else {
            p &= ~kClemensCPUStatus_Carry;
        }
        cpu->regs.A = (uint16_t)sbc;
    }
    cpu->regs.P = p;
}

static inline void _cpu_asl(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    uint8_t p = cpu->regs.P;
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        if (v & 0x80)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        v <<= 1;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data(cpu, v);
        *value = CLEM_UTIL_set16_lo(*value, v);
    } else {
        if (*value & 0x8000)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        *value <<= 1;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data_16(cpu, *value);
    }
}

static inline void _cpu_rol(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    uint8_t p = cpu->regs.P;
    bool next_carry;
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        next_carry = (v & 0x80) != 0;
        v <<= 1;
        if (p & kClemensCPUStatus_Carry)
            v |= 0x01;
        else
            v &= 0xfe;
        if (next_carry)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data(cpu, v);
        *value = CLEM_UTIL_set16_lo(*value, v);
    } else {
        next_carry = (*value & 0x8000) != 0;
        *value <<= 1;
        if (p & kClemensCPUStatus_Carry)
            *value |= 0x01;
        else
            *value &= 0xfffe;
        if (next_carry)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data_16(cpu, *value);
    }
}

static inline void _cpu_lsr(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    uint8_t p = cpu->regs.P;
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        if (v & 0x01)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        v >>= 1;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data(cpu, v);
        *value = CLEM_UTIL_set16_lo(*value, v);
    } else {
        if (*value & 0x0001)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        *value >>= 1;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data_16(cpu, *value);
    }
}

static inline void _cpu_ror(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    uint8_t p = cpu->regs.P;
    bool next_carry = (*value & 0x01) != 0;
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        v >>= 1;
        if (p & kClemensCPUStatus_Carry)
            v |= 0x80;
        else
            v &= 0x7f;
        if (next_carry)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data(cpu, v);
        *value = CLEM_UTIL_set16_lo(*value, v);
    } else {
        *value >>= 1;
        if (p & kClemensCPUStatus_Carry)
            *value |= 0x8000;
        else
            *value &= 0x7fff;
        if (next_carry)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data_16(cpu, *value);
    }
}

static inline void _cpu_cmp(struct Clemens65C816 *cpu, uint16_t reg, uint16_t value, bool is8) {
    uint32_t cmp;
    uint8_t p = cpu->regs.P;
    if (is8) {
        value = value & 0xff;
        cmp = (reg & 0xff);
        if (cmp >= value)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cmp -= value;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data(cpu, (uint8_t)cmp);
    } else {
        if (reg >= value)
            p |= kClemensCPUStatus_Carry;
        else
            p &= ~kClemensCPUStatus_Carry;
        cmp = reg;
        cmp -= value;
        cpu->regs.P = p;
        _cpu_p_flags_n_z_data_16(cpu, (uint16_t)cmp);
    }
}

static inline void _cpu_and(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    uint16_t and;
    if (is8) {
        value = value & 0xff;
        and = (cpu->regs.A & 0xff) & value;
        _cpu_p_flags_n_z_data(cpu, (uint8_t) and);
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, and);
    } else {
        and = cpu->regs.A & value;
        _cpu_p_flags_n_z_data_16(cpu, and);
        cpu->regs.A = and;
    }
}

static inline void _cpu_eor(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    uint16_t eor;
    if (is8) {
        value = value & 0xff;
        eor = (cpu->regs.A & 0xff) ^ value;
        _cpu_p_flags_n_z_data(cpu, (uint8_t)eor);
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, eor);
    } else {
        eor = cpu->regs.A ^ value;
        _cpu_p_flags_n_z_data_16(cpu, eor);
        cpu->regs.A = eor;
    }
}

static inline void _cpu_ora(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    uint16_t ora;
    if (is8) {
        value = value & 0xff;
        ora = (cpu->regs.A & 0xff) | value;
        _cpu_p_flags_n_z_data(cpu, (uint8_t)ora);
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, ora);
    } else {
        ora = cpu->regs.A | value;
        _cpu_p_flags_n_z_data_16(cpu, ora);
        cpu->regs.A = ora;
    }
}

static inline void _cpu_bit(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    if (is8) {
        uint8_t v = (uint8_t)(value);
        uint8_t a = (uint8_t)(cpu->regs.A);
        if (v & 0x40)
            cpu->regs.P |= kClemensCPUStatus_Overflow;
        else
            cpu->regs.P &= ~kClemensCPUStatus_Overflow;
        _cpu_p_flags_n_data(cpu, v);
        _cpu_p_flags_z_data(cpu, v & a);

    } else {
        if (value & 0x4000)
            cpu->regs.P |= kClemensCPUStatus_Overflow;
        else
            cpu->regs.P &= ~kClemensCPUStatus_Overflow;
        _cpu_p_flags_n_data_16(cpu, value);
        _cpu_p_flags_z_data_16(cpu, value & cpu->regs.A);
    }
}

static inline void _cpu_bit_imm(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    // immediate mode only affects the Z flag
    if (is8) {
        uint8_t v = (uint8_t)(value);
        uint8_t a = (uint8_t)(cpu->regs.A);
        _cpu_p_flags_z_data(cpu, v & a);
    } else {
        _cpu_p_flags_z_data_16(cpu, value & cpu->regs.A);
    }
}

static inline void _cpu_inc(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        ++v;
        _cpu_p_flags_n_z_data(cpu, v);
        *value = CLEM_UTIL_set16_lo(*value, v);
    } else {
        *value += 1;
        _cpu_p_flags_n_z_data_16(cpu, *value);
    }
}

static inline void _cpu_dec(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        --v;
        _cpu_p_flags_n_z_data(cpu, v);
        *value = CLEM_UTIL_set16_lo(*value, v);
    } else {
        *value -= 1;
        _cpu_p_flags_n_z_data_16(cpu, *value);
    }
}

static inline void _cpu_lda(struct Clemens65C816 *cpu, uint16_t value, bool is8) {
    if (is8) {
        _cpu_p_flags_n_z_data(cpu, (uint8_t)value);
        cpu->regs.A = CLEM_UTIL_set16_lo(cpu->regs.A, value);
    } else {
        _cpu_p_flags_n_z_data_16(cpu, value);
        cpu->regs.A = value;
    }
}

static inline void _cpu_ldxy(struct Clemens65C816 *cpu, uint16_t *reg, uint16_t value, bool is8) {
    if (is8) {
        _cpu_p_flags_n_z_data(cpu, (uint8_t)value);
        *reg = CLEM_UTIL_set16_lo(*reg, value);
    } else {
        _cpu_p_flags_n_z_data_16(cpu, value);
        *reg = value;
    }
}

static inline void _cpu_trb(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        uint8_t a = (uint8_t)(cpu->regs.A);
        _cpu_p_flags_z_data(cpu, v & a);
        v &= ~a;
        *value = CLEM_UTIL_set16_lo(cpu->regs.A, v);
    } else {
        _cpu_p_flags_z_data_16(cpu, *value & cpu->regs.A);
        *value &= ~cpu->regs.A;
    }
}

static inline void _cpu_tsb(struct Clemens65C816 *cpu, uint16_t *value, bool is8) {
    if (is8) {
        uint8_t v = (uint8_t)(*value);
        uint8_t a = (uint8_t)(cpu->regs.A);
        _cpu_p_flags_z_data(cpu, v & a);
        v |= a;
        *value = CLEM_UTIL_set16_lo(cpu->regs.A, v);
    } else {
        _cpu_p_flags_z_data_16(cpu, *value & cpu->regs.A);
        *value |= cpu->regs.A;
    }
}

static inline void _clem_write_816(ClemensMachine *clem, uint16_t value, uint16_t addr, uint8_t dbr,
                                   bool is8) {
    if (is8) {
        clem_write(clem, (uint8_t)value, addr, dbr, CLEM_MEM_FLAG_DATA);
    } else {
        _clem_write_16(clem, value, addr, dbr);
    }
}

static inline void _clem_write_indexed_816(ClemensMachine *clem, uint16_t value, uint16_t addr,
                                           uint16_t index, uint8_t dbr, bool is_data_8,
                                           bool is_index_8) {
    uint16_t eff_index = is_index_8 ? (index & 0xff) : index;
    uint16_t eff_addr = addr + eff_index;
    uint8_t dbr_actual;
    if (eff_addr < addr && !clem->cpu.pins.emulation) {
        _clem_next_dbr(clem, &dbr_actual, dbr);
    } else {
        dbr_actual = dbr;
    }
    if (is_data_8) {
        clem_write(clem, (uint8_t)value, eff_addr, dbr_actual, CLEM_MEM_FLAG_DATA);
    } else {
        _clem_write_16(clem, value, eff_addr, dbr_actual);
    }
}

static inline void _clem_branch(ClemensMachine *clem, uint16_t *pc, int8_t offset, bool do_branch) {
    if (!do_branch)
        return;
    uint16_t tmp_addr = *pc + offset;
    if (clem->cpu.pins.emulation && CLEM_UTIL_CROSSED_PAGE_BOUNDARY(*pc, tmp_addr)) {
        _clem_cycle(clem);
    }
    _clem_cycle(clem);
    *pc = tmp_addr;
}

static inline uint16_t _clem_read_interrupt_vector(ClemensMachine *clem, uint16_t lo, uint16_t hi) {
    /* Tech Note # 68
       http://www.1000bit.it/support/manuali/apple/technotes/iigs/tn.iigs.068.html

       Note: Interrupt vectors are always pulled from ROM regardless of
       whether or not the language card soft-switches have ROM enabled,
       providing that the I/O shadowing for banks $00/01 is enabled
       -- which it always is when running Apple IIGS or Apple II system
       software
   */
    uint16_t tmp_addr;
    uint8_t tmp_data;
    uint8_t src_bank;

    if ((*clem->mem.mmio_niolc)(&clem->mem)) {
        /* this should map to RAM and override language card bank mapping */
        src_bank = 0x00;
    } else {
        /* grab the vector from ROM always */
        src_bank = 0xff;
    }
    clem_read(clem, &tmp_data, lo, src_bank, CLEM_MEM_FLAG_PROGRAM);
    tmp_addr = tmp_data;
    clem_read(clem, &tmp_data, hi, src_bank, CLEM_MEM_FLAG_PROGRAM);

    return ((uint16_t)tmp_data << 8) | tmp_addr;
}

static inline void _clem_irq_brk_setup(ClemensMachine *clem, uint8_t *pbr, uint16_t *pc,
                                       uint16_t vlo, uint16_t vhi, bool is_brk) {
    /*
        pass PC into function since instructions modify may modify the current
            PC register.

        if native push PBR
        push PCH, PCL
        push P
        irq disable, decimal mode cleared
        clear PBR
        3 cycles in emulation
        4 cycles in native (+PBR)
    */
    struct Clemens65C816 *cpu = &clem->cpu;
    if (!cpu->pins.emulation) {
        _clem_opc_push_reg_8(clem, cpu->regs.PBR);
    }
    _clem_opc_push_reg_816(clem, *pc, false);
    _clem_opc_push_status(clem, !is_brk);
    //  65816 always disables decimal mode on interrupts, even in emulation
    cpu->regs.P &= ~kClemensCPUStatus_Decimal;
    cpu->regs.P |= kClemensCPUStatus_IRQDisable;
    *pbr = 0x00;
    *pc = _clem_read_interrupt_vector(clem, vlo, vhi);
}

static inline uint16_t _clem_irq_brk_return(ClemensMachine *clem) {
    /*  called from RTI
        pop P
        pop PCL, PCH
        if native pull PBR
        +3/4 cycles (emulation/native)
    */
    uint16_t tmp_addr;
    uint8_t tmp_bnk0;

    struct Clemens65C816 *cpu = &clem->cpu;

    _clem_opc_pull_status(clem);
    _clem_opc_pull_reg_816(clem, &tmp_addr, false);
    if (!cpu->pins.emulation) {
        _clem_opc_pull_reg_8(clem, &tmp_bnk0);
        cpu->regs.PBR = tmp_bnk0;
    }
    return tmp_addr;
}