Function encodeAddress

NULLC/Translator_X86.cpp:24–87

encode [base], [base+displacement], [index*multiplier+displacement] and [index*multiplier+base+displacement]

// encode [base], [base+displacement], [index*multiplier+displacement] and [index*multiplier+base+displacement]
unsigned int	encodeAddress(unsigned char* stream, x86Reg index, int multiplier, x86Reg base, int displacement, char spareField)
{
	assert(index != rESP);
	unsigned char* start = stream;

	bool dispImm8 = (char)(displacement) == displacement && base != rNONE;

	unsigned char mod = 0;
	if(displacement)
	{
		if(dispImm8)
			mod = 1 << 6;
		else
			mod = 2 << 6;
	}

	// special case: [ebp] should be encoded as [ebp+0]
	if(displacement == 0 && base == rEBP)
		mod = 1 << 6;
	if(index == rNONE && base == rNONE)
		mod = 0;

	unsigned char spare = spareField << 3;

	unsigned char RM = regCode[rEBP]; // by default, it's simply [displacement]
	if(base != rNONE)
		RM = regCode[base];	// this is [base + displacement]
	if(index != rNONE)
		RM = regCode[rESP];	// this changes mode to [index*multiplier + base + displacement]

	unsigned char sibBase = regCode[base];

	if(index != rNONE && base == rNONE)
	{
		mod = 0;
		sibBase = regCode[rEBP];
	}

	*stream++ = mod | spare | RM;
	unsigned char sibScale = 0;
	if(multiplier == 2)
		sibScale = 1 << 6;
	else if(multiplier == 4)
		sibScale = 2 << 6;
	else if(multiplier == 8)
		sibScale = 3 << 6;
	assert(multiplier == 0 || multiplier == 1 || multiplier == 2 || multiplier == 4 || multiplier == 8);

	unsigned char sibIndex = (index != rNONE ? regCode[index] << 3 : regCode[rESP] << 3);
	
	if(index != rNONE || base == rESP)
		*stream++ = sibScale | sibIndex | sibBase;
	
	if(dispImm8)
	{
		*stream = (char)displacement;
		if(mod)
			stream++;