A.5.318 UCOMISD: Unordered Scalar Double-Precision FP compare and set EFLAGS
UCOMISD xmm1,xmm2/m128 ; 66 0F 2E /r [WILLAMETTE,SSE2]
UCOMISD compares the low-order double-precision FP numbers in the two
operands, and sets the ZF, PF and CF bits in the EFLAGS register. In
addition, the OF, SF and AF bits in the EFLAGS register are zeroed out.
The unordered predicate (ZF, PF and CF all set) is returned if either
source operand is a "NaN" ("qNaN" or "sNaN").