A.5.32 COMISD: Scalar Ordered Double-Precision FP Compare and Set EFLAGS
COMISD xmm1,xmm2/mem64 ; 66 0F 2F /r [WILLAMETTE,SSE2]
COMISD compares the low-order double-precision FP value in the two
source operands. ZF, PF and CF are set according to the result. OF, AF
and AF are cleared. The unordered result is returned if either source is
a NaN (QNaN or SNaN).
The destination operand is an XMM register. The source can be either an
XMM register or a memory location.
The flags are set according to the following rules:
Result Flags Values
UNORDERED: ZF,PF,CF <-- 111;
GREATER_THAN: ZF,PF,CF <-- 000;
LESS_THAN: ZF,PF,CF <-- 001;
EQUAL: ZF,PF,CF <-- 100;