x86 Instruction Set Reference

Moves a scalar single-precision floating-point value from the source operand (second operand) to the destination operand (first operand). The source and destination operands can be XMM registers or 32-bit memory locations. This instruction can be used to move a single-precision floating-point value to and from the low doubleword of an XMM register and a 32-bit memory location, or to move a single-precision floating-point value between the low doublewords of two XMM registers. The instruction cannot be used to transfer data between memory locations.

When the source and destination operands are XMM registers, the three high-order doublewords of the destination operand remain unchanged. When the source operand is a memory location and destination operand is an XMM registers, the three high-order doublewords of the destination operand are cleared to all 0s.

//MOVSS instruction when source and destination operands are XMM registers:
if(IsXMM(Source) && IsXMM(Destination)) Destination[0..31] = Source[0..31];
//Destination[32..127] remains unchanged
//MOVSS instruction when source operand is XMM register and destination operand is memory location:
else if(IsXMM(Source) && IsMemory(Destination)) Destination = Source[0..31];
//MOVSS instruction when source operand is memory location and destination operand is XMM register:
else {
	Destination[0..31] = Source;
	Destination[32..127] = 0;
}