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//	6502.h
//	Core elements of the 6502 CPU

typedef unsigned char byte;
typedef unsigned short address;
byte acc, X, Y, P, S = 0x00;
address PC = 0x0000;
byte Memory[4096]; // TO DO. Add expansion capability to memory.

//	FLAGS
#define flag_N 0x80 // Negative
#define flag_V 0x40	// Overflow
#define flag_B 0x10	// BRK command
#define flag_D 0x08	// Decimal mode
#define flag_I 0x04	// IRQ disable
#define flag_Z 0x02	// Zero
#define flag_C 0x01	// Carry

byte getFlag(byte flag) {
	return ((P & flag) == flag) ? 1 : 0;
}

void setFlag(byte flag, int x) {
	if (x == 1){
		if ((P & flag) == 0x0)	P += flag;
	}else if (x == 0){
		if ((P & flag) == flag)	P -= flag;
	}
	else{
		fprintf(stderr, "setFlag() passed arg neither 0 or 1");
	}
}

void flagSet(byte flag){
	P |= flag;
}

void flagClear(byte flag){
	P &= ~flag;
}


//	BCD
// need to actually look into BCD on the 6502
byte toBCD(byte x){
	if (x < 100){
		byte a = ((x / 10) << 4);
		byte b = (x % 10);
		return (a + b);
	}
	else{
		fprintf(stderr, "Number greater than 99 passed to toBCD()");
	}
}

byte fromBCD(byte x){
	byte a = ((x >> 4) * 10);
	byte b = (x & 0xF);
	return (a + b);
}


//	Functions which perform reusable routines for finding if a specific flag should be set.

void setFlagN(byte x){
	if (x & flag_N == flag_N)
		setFlag(flag_N, 1);
	else
		setFlag(flag_N, 0);
}

//Perform prior to any changes
void setFlagV(byte x, byte y){
	if ((x & flag_N) == (y & flag_N)){
		if (((x + y) & (flag_N ^ 0xFF)) > 0x7F) setFlag(flag_V, 1);
		else setFlag(flag_V, 0);
	}else{
		if (((x - y) & (flag_N ^ 0xFF)) > 0x7F) setFlag(flag_V, 1);
		else setFlag(flag_V, 0);
	}
}

/*void setFlagB(){ //WORK ON
	setFlag(flag_B, 1);
}*/ //Dont really need since its dependent on the BRK insturction

/*void setFlagD(){
	setFlag(flag_D, 1);
}*/

/*void setFlagI(){ //WORK ON
	setFlag(flag_Z, 1);
}*/

void setFlagZ(int x){
	if (x == 0)
		setFlag(flag_Z, 1);
	else
		setFlag(flag_Z, 0);
}

//Only 6 instructions, 2 not including stack instructions, use the carry flag.
// Need to look further into implementation details for this.
/*void setFlagC(){
	setFlag(flag_Z, 1);
}*/