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INSTRUCTION SET REFERENCE
UCOMISS—Unordered Scalar Single-FP compare and set EFLAGS
(Continued)
Virtual 8086 Mode Exceptions
Same exceptions as in Real Address Mode.
#AC
For unaligned memory reference if the current privilege level is 3.
#PF (fault-code) For a page fault.
Comments
UCOMISS differs from COMISS in that it signals an invalid numeric exception when a source
operand is an sNaN; COMISS signals invalid if a source operand is either a qNaN or an sNaN.
The usage of Repeat (F2H, F3H) and Operand-size (66H) prefixes with UCOMISS is reserved.
Different processor implementations may handle these prefixes differently. Usage of these
prefixes with UCOMISS risks incompatibility with future processors.
