Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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FTST Instruction
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  Title:    Test for Zero
 
  Syntax:   FTST
 
  See also: FCOM, Status Word
 
  Description:
 
     Compares ST with +0.0 and sets the condition of the status word
     according to the result.
 
     The condition codes for FTST are as follows:
 
     C3     C2     C1     C0     Meaning
 
     0      0      ?      0      ST is positive
     0      0      ?      1      ST is negative
     1      0      ?      0      ST is 0
     1      1      ?      1      ST is not comparable (NAN or
                                 projective infinity)
                                    -♦-