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  Title:    Compare String                        Flags: O D I T S Z A P C
                                                         ═════════════════
  Syntax:   CMPS dest,src                                ±       ± ± ± ± ±
            CMPSB
            CMPSW
            CMPSD (80386/486 Only)
 
  See also: REPE, SCAS, JCXZ, CLD, CMP
 
  Description:
 
     Compares two strings. DS:SI must point to the source string and
     ES:DI must point to the destination string (even if operands are
     given). For each comparison, the destination element is subtracted
     from the source element and the flags are updated to reflect the
     result (although the result is not stored).
 
     DI and SI are adjusted according to the size of the operands and
     the status of the direction flag. They are increased if the
     direction flag has been cleared with CLD, or decreased if the
     direction flag has been set with STD.
 
     If the CMPS form of the instruction is used, operands must be
     provided to indicate the size of the data elements to be
     processed. A segment override can be given for the source (but not
     for the destination). If CMPSB (bytes), CMPSW (words), or CMPSD
     (doublewords) is used, the instruction determines the size of the
     data elements to be processed.
 
     CMPS and its variations are normally used with repeat prefixes:
     REPNE (or REPNZ) finds the first match between two strings; REPE
     (or REPZ) finds the first mismatch.
 
     Before the comparison, CX should contain the maximum number of
     elements to compare. After a REPNE CMPS, the zero flag is
     clear if no match was found. After REPE CMPS, the zero flag
     is set if no mismatch was found. Otherwise, SI and DI will
     point to the element after the first match or nonmatch.
 
     When the instruction finishes, ES:DI and DS:SI point to the
     element that follows (if the direction flag is clear) or
     precedes (if the direction flag is set) the match or mismatch.
     If CX decrements to 0, ES:DI and DS:SI point to the element
     that follows or precedes the last comparison. The zero flag is
     set or clear according to the result of the last comparison, not
     according to the value of CX.
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