A.5.149 MAXSD: Return Scalar Double-Precision FP Maximum
MAXSD xmm1,xmm2/m64 ; F2 0F 5F /r [WILLAMETTE,SSE2]
MAXSD compares the low-order double-precision FP numbers from xmm1 and
xmm2/mem, and stores the maximum value in xmm1. If the values being
compared are both zeroes, source2 (xmm2/m64) would be returned. If
source2 (xmm2/m64) is an SNaN, this SNaN is forwarded unchanged to the
destination (i.e., a QNaN version of the SNaN is not returned). The high
quadword of the destination is left unchanged.