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Cleanup SBC functions

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This commit is contained in:
Palindromic Bread Loaf
2025-07-28 12:26:21 -04:00
parent ecca099d81
commit 015b039fff
2 changed files with 45 additions and 196 deletions
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238
src/cpu.cpp
View File

@@ -478,6 +478,26 @@ uint16_t CPU::SBC16_Decimal(const uint16_t a, const uint16_t operand, const bool
return final_result;
}
void CPU::SBC_FromAddress(const uint32_t address, const int base_cycles_8bit, const int base_cycles_16bit) {
if (P & FLAG_M) {
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += base_cycles_8bit;
} else {
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += base_cycles_16bit;
}
}
void CPU::SBC_FromAddress_PageCross(const uint32_t address, const uint16_t base_address, const uint16_t offset, const int base_cycles_8bit, const int base_cycles_16bit) {
SBC_FromAddress(address, base_cycles_8bit, base_cycles_16bit);
if ((base_address & 0xFF00) != ((base_address + offset) & 0xFF00)) {
cycles++;
}
}
void CPU::ExecuteInstruction() {
switch (const uint8_t opcode = bus->Read(PC++)) {
// ADC - Add with Carry
@@ -4416,15 +4436,11 @@ void CPU::RTI() {
void CPU::SBC_Immediate() {
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(PC++);
SBC8(operand);
SBC8(ReadByte(PC++));
cycles += 2;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(PC);
SBC16(ReadWord(PC));
PC += 2;
SBC16(operand);
cycles += 3;
}
}
@@ -4432,35 +4448,12 @@ void CPU::SBC_Immediate() {
void CPU::SBC_Absolute() {
const uint16_t address = ReadWord(PC);
PC += 2;
const uint32_t full_address = (DB << 16) | address;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(full_address);
SBC8(operand);
cycles += 4;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(full_address);
SBC16(operand);
cycles += 5;
}
SBC_FromAddress((DB << 16) | address, 4, 5);
}
void CPU::SBC_AbsoluteLong() {
const uint32_t address = ReadByte(PC++) | (ReadByte(PC++) << 8) | (ReadByte(PC++) << 16);
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 5;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 6;
}
SBC_FromAddress(address, 5, 6);
}
void CPU::SBC_AbsoluteX() {
@@ -4469,41 +4462,14 @@ void CPU::SBC_AbsoluteX() {
const uint16_t x_offset = (P & FLAG_X) ? (X & 0xFF) : X;
const uint32_t address = (DB << 16) | (base_address + x_offset);
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 4;
if ((base_address & 0xFF00) != ((base_address + x_offset) & 0xFF00)) {
cycles++;
}
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 5;
if ((base_address & 0xFF00) != ((base_address + x_offset) & 0xFF00)) {
cycles++;
}
}
SBC_FromAddress_PageCross(address, base_address, x_offset, 4, 5);
}
void CPU::SBC_AbsoluteLongX() {
const uint32_t base_address = ReadByte(PC++) | (ReadByte(PC++) << 8) | (ReadByte(PC++) << 16);
const uint16_t x_offset = (P & FLAG_X) ? (X & 0xFF) : X;
const uint32_t address = base_address + x_offset;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 5;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 6;
}
SBC_FromAddress(base_address + x_offset, 5, 6);
}
void CPU::SBC_AbsoluteY() {
@@ -4512,41 +4478,14 @@ void CPU::SBC_AbsoluteY() {
const uint16_t y_offset = (P & FLAG_X) ? (Y & 0xFF) : Y;
const uint32_t address = (DB << 16) | (base_address + y_offset);
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 4;
if ((base_address & 0xFF00) != ((base_address + y_offset) & 0xFF00)) {
cycles++;
}
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 5;
if ((base_address & 0xFF00) != ((base_address + y_offset) & 0xFF00)) {
cycles++;
}
}
SBC_FromAddress_PageCross(address, base_address, y_offset, 4, 5);
}
void CPU::SBC_DirectPage() {
const uint8_t offset = ReadByte(PC++);
const uint32_t address = D + offset;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 3;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 4;
}
SBC_FromAddress(address, 3, 4);
if (D & 0xFF) cycles++;
}
@@ -4555,18 +4494,7 @@ void CPU::SBC_DirectPageX() {
const uint16_t x_offset = (P & FLAG_X) ? (X & 0xFF) : X;
const uint32_t address = D + offset + x_offset;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 4;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 5;
}
SBC_FromAddress(address, 4, 5);
if (D & 0xFF) cycles++;
}
@@ -4576,40 +4504,18 @@ void CPU::SBC_DirectPageIndirect() {
const uint16_t address = ReadWord(indirect_addr);
const uint32_t final_address = (DB << 16) | address;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(final_address);
SBC8(operand);
cycles += 5;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(final_address);
SBC16(operand);
cycles += 6;
}
SBC_FromAddress(final_address, 5, 6);
if (D & 0xFF) cycles++;
}
void CPU::SBC_DirectPageIndirectLong() {
const uint8_t offset = ReadByte(PC++);
const uint32_t indirect_addr = D + offset;
const uint32_t address = ReadByte(indirect_addr) |
(ReadByte(indirect_addr + 1) << 8) |
(ReadByte(indirect_addr + 2) << 16);
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 6;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 7;
}
const uint32_t address = ReadByte(indirect_addr)
| (ReadByte(indirect_addr + 1) << 8)
| (ReadByte(indirect_addr + 2) << 16);
SBC_FromAddress(address, 6, 7);
if (D & 0xFF) cycles++;
}
@@ -4620,48 +4526,19 @@ void CPU::SBC_DirectPageIndirectY() {
const uint16_t y_offset = (P & FLAG_X) ? (Y & 0xFF) : Y;
const uint32_t address = (DB << 16) | (base_address + y_offset);
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 5;
if ((base_address & 0xFF00) != ((base_address + y_offset) & 0xFF00)) {
cycles++;
}
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 6;
if ((base_address & 0xFF00) != ((base_address + y_offset) & 0xFF00)) {
cycles++;
}
}
SBC_FromAddress_PageCross(address, base_address, y_offset, 5, 6);
if (D & 0xFF) cycles++;
}
void CPU::SBC_DirectPageIndirectLongY() {
const uint8_t offset = ReadByte(PC++);
const uint32_t indirect_addr = D + offset;
const uint32_t base_address = ReadByte(indirect_addr) |
(ReadByte(indirect_addr + 1) << 8) |
(ReadByte(indirect_addr + 2) << 16);
const uint32_t base_address = ReadByte(indirect_addr)
| (ReadByte(indirect_addr + 1) << 8)
| (ReadByte(indirect_addr + 2) << 16);
const uint16_t y_offset = (P & FLAG_X) ? (Y & 0xFF) : Y;
const uint32_t address = base_address + y_offset;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 6;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 7;
}
SBC_FromAddress(base_address + y_offset, 6, 7);
if (D & 0xFF) cycles++;
}
@@ -4672,18 +4549,7 @@ void CPU::SBC_DirectPageIndirectX() {
const uint16_t address = ReadWord(indirect_addr);
const uint32_t final_address = (DB << 16) | address;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(final_address);
SBC8(operand);
cycles += 6;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(final_address);
SBC16(operand);
cycles += 7;
}
SBC_FromAddress(final_address, 6, 7);
if (D & 0xFF) cycles++;
}
@@ -4691,17 +4557,7 @@ void CPU::SBC_StackRelative() {
const uint8_t offset = ReadByte(PC++);
const uint32_t address = SP + offset;
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 4;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 5;
}
SBC_FromAddress(address, 4, 5);
}
void CPU::SBC_StackRelativeIndirectY() {
@@ -4711,17 +4567,7 @@ void CPU::SBC_StackRelativeIndirectY() {
const uint16_t y_offset = (P & FLAG_X) ? (Y & 0xFF) : Y;
const uint32_t address = (DB << 16) | (base_address + y_offset);
if (P & FLAG_M) {
// 8-bit mode
const uint8_t operand = ReadByte(address);
SBC8(operand);
cycles += 7;
} else {
// 16-bit mode
const uint16_t operand = ReadWord(address);
SBC16(operand);
cycles += 8;
}
SBC_FromAddress(address, 7, 8);
}
void CPU::SEC() {

3
src/cpu.h
View File

@@ -91,6 +91,9 @@ class CPU {
void SBC16(uint16_t operand);
uint8_t SBC8_Decimal(uint8_t a, uint8_t operand, bool carry);
uint16_t SBC16_Decimal(uint16_t a, uint16_t operand, bool carry);
void SBC_FromAddress(uint32_t address, int base_cycles_8bit, int base_cycles_16bit);
void SBC_FromAddress_PageCross(uint32_t address, uint16_t base_address, uint16_t offset, int base_cycles_8bit,
int base_cycles_16bit);
public:
explicit CPU(Bus* memory_bus) : bus(memory_bus) {