NASM 2.05 based x86 Instruction Reference[ch025]
A.5.6 ADDSD: ADD Scalar Double-Precision FP Values ADDSD xmm1,xmm2/mem64 ; F2 0F 58 /r [KATMAI,SSE] ADDSD adds the low double-precision FP values from the source and destination operands and stores the double-precision FP result in the destination operand. dst[0-63] := dst[0-63] + src[0-63], dst[64-127) remains unchanged. The destination is an XMM register. The source operand can be either an XMM register or a 64-bit memory location.