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  Title:    Unordered Compare
            80387/486 Only
 
  Syntax:   FUCOM [src]
            FUCOMP [src]
            FUCOMPP
 
  See also: FCOM, FTST, Status Word
 
  Description:
 
     Compares the specified source to ST and sets the condition codes
     of the status word according to the result. The instruction
     subtracts the source operand from ST without changing either
     operand. Memory operands are not allowed.
 
     If no operand is specified or if two pops are specified, ST is
     compared to ST(1). If one pop is specified with an operand, the
     given register is compared to ST.
 
     Unlike FCOM, FUCOM does not cause an invalid-operation exception
     if one of the operands is a NAN. Instead, the condition codes are
     set to unordered.
 
     The condition codes for FUCOM are as follows:
 
     C3     C2     C1     C0     Meaning
 
     0      0      ?      0      ST > source
     0      0      ?      1      ST < source
     1      0      ?      0      ST = source
     1      1      ?      1      Unordered
                                    -♦-