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(nasm.info)Section B.4.73

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B.4.73. `FCOM', `FCOMP', `FCOMPP', `FCOMI', `FCOMIP': Floating-Point Compare
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     FCOM mem32                    ; D8 /2                [8086,FPU]
     FCOM mem64                    ; DC /2                [8086,FPU]
     FCOM fpureg                   ; D8 D0+r              [8086,FPU]
     FCOM ST0,fpureg               ; D8 D0+r              [8086,FPU]

     FCOMP mem32                   ; D8 /3                [8086,FPU]
     FCOMP mem64                   ; DC /3                [8086,FPU]
     FCOMP fpureg                  ; D8 D8+r              [8086,FPU]
     FCOMP ST0,fpureg              ; D8 D8+r              [8086,FPU]

     FCOMPP                        ; DE D9                [8086,FPU]

     FCOMI fpureg                  ; DB F0+r              [P6,FPU]
     FCOMI ST0,fpureg              ; DB F0+r              [P6,FPU]

     FCOMIP fpureg                 ; DF F0+r              [P6,FPU]
     FCOMIP ST0,fpureg             ; DF F0+r              [P6,FPU]

   `FCOM' compares `ST0' with the given operand, and sets the FPU flags
accordingly. `ST0' is treated as the left-hand side of the comparison,
so that the carry flag is set (for a `less-than' result) if `ST0' is
less than the given operand.

   `FCOMP' does the same as `FCOM', but pops the register stack
afterwards. `FCOMPP' compares `ST0' with `ST1' and then pops the
register stack twice.

   `FCOMI' and `FCOMIP' work like the corresponding forms of `FCOM' and
`FCOMP', but write their results directly to the CPU flags register
rather than the FPU status word, so they can be immediately followed by
conditional jump or conditional move instructions.

   The `FCOM' instructions differ from the `FUCOM' instructions (*Note
Section B.4.108::) only in the way they handle quiet NaNs: `FUCOM' will
handle them silently and set the condition code flags to an `unordered'
result, whereas `FCOM' will generate an exception.