NASM 2.05 based x86 Instruction Reference[ch348]
A.5.322 UNPCKHPD: Unpack and Interleave High Packed Double-Precision FP Values UNPCKHPD xmm1,xmm2/m128 ; 66 0F 15 /r [WILLAMETTE,SSE2] UNPCKHPD performs an interleaved unpack of the high-order data elements of the source and destination operands, saving the result in "xmm1". It ignores the lower half of the sources. The operation of this instruction is: dst[63-0] := dst[127-64]; dst[127-64] := src[127-64].