NASM 2.05 based x86 Instruction Reference[ch172]
A.5.150 MAXSS: Return Scalar Single-Precision FP Maximum MAXSS xmm1,xmm2/m32 ; F3 0F 5F /r [KATMAI,SSE] MAXSS compares the low-order single-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/m32) would be returned. If source2 (xmm2/m32) is an SNaN, this SNaN is forwarded unchanged to the destination (i.e., a QNaN version of the SNaN is not returned). The high three doublewords of the destination are left unchanged.