path: root/src/cpu/instructions.c

//	instructions.c
//	Definition of all instruction functions, handling effect of instruction and flags.

#include"instructions.h"

struct State state;


// Load and Store Instructions

void PageBoundary(Addressing r) {
	switch(r)
		{
		case eAbsoluteIndexedX: 
			if ((state.address & 0xFF00) != ((state.address + X) & 0xFF00))
				state.cycles++;
			break;
		case eAbsoluteIndexedY: 
			if ((state.address & 0xFF00) != ((state.address + Y) & 0xFF00))
				state.cycles++;
			break;
		case eIndirectIndexed:
			if ((state.address & 0xFF00) != (state.address - Y & 0xFF00))
				state.cycles++;
			break;
		case eRelative:
			// Assuming that this goes at the end of the break function.
			if ((PC & 0xFF00) != ((PC - (char)state.value) & 0xFF00))
				state.cycles++;
			break;
		}
}


void LDA(Addressing addr){
	acc = state.value;
	SetFlag_N(acc);
	SetFlag_Z(acc);
	PageBoundary(addr);
}

void LDX(Addressing addr){
	X = state.value;
	SetFlag_N(X);
	SetFlag_Z(X);
	PageBoundary(addr);
}

void LDY(Addressing addr){
	Y = state.value;
	SetFlag_N(Y);
	SetFlag_Z(Y);
	PageBoundary(addr);
}

void STA(Addressing addr){
	SetMemory(state.address, acc);
}

void STX(Addressing addr){
	SetMemory(state.address, X);
}

void STY(Addressing addr){
	SetMemory(state.address, Y);
}

// Arithmetic Instructions
// TODO: Add BCD arithmetic modes.

void ADC(Addressing addr){
	byte buffer = acc + state.value + GetFlag(flag_C);

	SetFlag_V(buffer, acc);

	SetFlag(flag_C, (buffer < acc) ? 1 : 0);
	
	acc = buffer;
	SetFlag_N(acc);
	SetFlag_Z(acc);
	PageBoundary(addr);
}

void SBC(Addressing addr){
	byte buffer = acc - state.value - !GetFlag(flag_C);
        
	SetFlag_V(buffer, acc);

	SetFlag(flag_C, (buffer > acc) ? 0 : 1);

	acc = buffer;
	
	SetFlag_N(acc);
	SetFlag_Z(acc);
	PageBoundary(addr);
}


//Increment and Decrement Instructions

void INC(Addressing addr){
	byte a = state.value;
	SetMemory(state.address, ++a);
	SetFlag_N(a);
	SetFlag_Z(a);
}

void INX(Addressing addr){
	X++;
	SetFlag_N(X);
	SetFlag_Z(X);
}

void INY(Addressing addr){
	Y++;
	SetFlag_N(Y);
	SetFlag_Z(Y);
}

void DEC(Addressing addr){
	byte a = state.value;
	SetMemory(state.address, --a);
	SetFlag_N(a);
	SetFlag_Z(a);
}

void DEX(Addressing addr){
	X--;
	SetFlag_N(X);
	SetFlag_Z(X);
}

void DEY(Addressing addr){
	Y--;
	SetFlag_N(Y);
	SetFlag_Z(Y);
}


// Logical Instructions

void AND(Addressing addr){
	acc &= state.value;
	SetFlag_N(acc);
	SetFlag_Z(acc);
	PageBoundary(addr);
}

void ORA(Addressing addr){
	acc |= state.value;
	SetFlag_N(acc);
	SetFlag_Z(acc);
	PageBoundary(addr);
}

void EOR(Addressing addr){
	acc ^= state.value;
	SetFlag_N(acc);
	SetFlag_Z(acc);
	PageBoundary(addr);
}


// Jump, Branch, Compare, and Test Bits

void JMP(Addressing addr){
	PC = state.address - state.length;
}

void BCC(Addressing addr){
	if (GetFlag(flag_C) == 0) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BCS(Addressing addr){
	if (GetFlag(flag_C) == 1) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BEQ(Addressing addr){
	if (GetFlag(flag_Z) == 1) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BNE(Addressing addr){
	if (GetFlag(flag_Z) == 0) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BMI(Addressing addr){
	if (GetFlag(flag_N) == 1) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BPL(Addressing addr){
	if (GetFlag(flag_N) == 0) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BVS(Addressing addr){
	if (GetFlag(flag_V) == 1) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void BVC(Addressing addr){
	if (GetFlag(flag_V) == 0) {
		PC += (char)state.value;
		state.cycles++;
		PageBoundary(addr);
	}
}

void CMP(Addressing addr){
	SetFlag(flag_C, (acc >= state.value) ? 1 : 0);
	SetFlag(flag_Z, (acc == state.value) ? 1 : 0);
	SetFlag(flag_N, (acc  < state.value) ? 1 : 0);
	PageBoundary(addr);
}

void CPX(Addressing addr){
	SetFlag(flag_C, (X >= state.value) ? 1 : 0);
	SetFlag(flag_Z, (X == state.value) ? 1 : 0);
	SetFlag(flag_N, (X  < state.value) ? 1 : 0);
}

void CPY(Addressing addr){
	SetFlag(flag_C, (Y >= state.value) ? 1 : 0);
	SetFlag(flag_Z, (Y == state.value) ? 1 : 0);
	SetFlag(flag_N, (Y  < state.value) ? 1 : 0);
}

void BIT(Addressing addr){
	SetFlag(flag_N, ((state.value & flag_N) != 0));
	SetFlag(flag_V, ((state.value & flag_V) != 0));
	SetFlag(flag_Z, ((state.value &    acc) == 0));
}


// Shift and Rotate Instructions

void ASL(Addressing addr){
	byte m = (addr == eAccumulator) ? acc : state.value;
	
	SetFlag(flag_C, (m & 0b10000000));
	m = (m << 1) & 0b11111110;
	SetFlag_N(m);
	SetFlag_Z(m);
	
	(addr == eAccumulator)
	?	acc = m
	:	SetMemory(state.address, m);
}

void LSR(Addressing addr) {
	byte m = (addr == eAccumulator) ? acc : state.value;
	
	SetFlag(flag_C, (m & 0b00000001));
	m = (m >> 1) & 0b01111111;
	SetFlag_N(m);
	SetFlag_Z(m);
	
	(addr == eAccumulator)
	?	acc = m
	:	SetMemory(state.address, m);
}

void ROL(Addressing addr){
	byte m = (addr == eAccumulator) ? acc : state.value;
	
	byte flag_store = (m & 0b10000000);
	m = (m << 1) & 0b11111110;
	m |= (GetFlag(flag_C)) ? 0b00000001 : 0;
	SetFlag(flag_C, flag_store);
	SetFlag_N(m);
	SetFlag_Z(m);
	
	(addr == eAccumulator)
	?	acc = m
	:	SetMemory(state.address, m);
}

void ROR(Addressing addr){
	byte m = (addr == eAccumulator) ? acc : state.value;

	byte flag_store = (m & 0b00000001);
	m = (m >> 1) & 0b01111111;
	m |= (GetFlag(flag_C)) ? 0b10000000 : 0;
	SetFlag(flag_C, flag_store);
	SetFlag_N(m);
	SetFlag_Z(m);
	
	
	(addr == eAccumulator)
	?	acc = m
	:	SetMemory(state.address, m);
}


// Transfer Instructions

void TAX(Addressing addr){
	X = acc;
	SetFlag_N(X);
	SetFlag_Z(X);
}

void TAY(Addressing addr){
	Y = acc;
	SetFlag_N(Y);
	SetFlag_Z(Y);
}

void TXA(Addressing addr){
	acc = X;
	SetFlag_N(acc);
	SetFlag_Z(acc);
}

void TYA(Addressing addr){
	acc = Y;
	SetFlag_N(acc);
	SetFlag_Z(acc);
}


// Stack Instructions

void TSX(Addressing addr){
	X = S;
}

void TXS(Addressing addr){
	S = X;
}

void PHA(Addressing addr){
	SetStack(acc);
}

void PHP(Addressing addr){
	SetStack(P);
}

void PLA(Addressing addr){
	acc = GetStack();
}

void PLP(Addressing addr){
	P = GetStack();
}


// Subroutine Instructions

void JSR(Addressing addr){
	SetStack ((PC+state.length) >> 8);
	SetStack(((PC+state.length) & 0x00FF) - 1);
	PC = state.address;
	PC -= state.length;
}

void RTS(Addressing addr){
	PC  =  (address)(GetStack()) + 1;
	PC += ((address)(GetStack())) << 8;
	PC -= state.length;
}

void RTI(Addressing addr){
	P = GetStack();
	PC  = (address)(GetStack());
	PC += (address)(GetStack() << 8);
}


// Set/Reset Insutrctions

void CLC(Addressing addr){
	SetFlag(flag_C, 0);
}

void CLD(Addressing addr){
	SetFlag(flag_D, 0);
}

void CLI(Addressing addr){
	SetFlag(flag_I, 0);
}

void CLV(Addressing addr){
	SetFlag(flag_V, 0);
}

void SEC(Addressing addr){
	SetFlag(flag_C, 1);
}

void SED(Addressing addr){
	SetFlag(flag_D, 1);
}

void SEI(Addressing addr){
	SetFlag(flag_I, 1);
}


// NOP/BRK Instructions

void NOP(Addressing addr){
}

void BRK(Addressing addr){
	SetStack((((PC+2) & 0xFF00) >> 8));
	SetStack((PC+2) & 0x00FF);
	SetStack(P);
	PC = (address)(GetMemory(0xFFFE));
	PC += ((address)(GetMemory(0xFFFF)) << 8);
}