NASM 2.05 based x86 Instruction Reference[ch026]
A.5.7 ADDSS: ADD Scalar Single-Precision FP Values ADDSS xmm1,xmm2/mem32 ; F3 0F 58 /r [WILLAMETTE,SSE2] ADDSS adds the low single-precision FP values from the source and destination operands and stores the single-precision FP result in the destination operand. dst[0-31] := dst[0-31] + src[0-31], dst[32-127] remains unchanged. The destination is an XMM register. The source operand can be either an XMM register or a 32-bit memory location.