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BYTEXOR.PRG
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1991-08-16
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/*
* File......: BYTEXOR.PRG
* Author....: Forest Belt, Computer Diagnostic Services, Inc.
* Date......: $Date: 16 Aug 1991 19:35:48 $
* Revision..: $Revision: 1.3 $
* Log file..: $Logfile: E:/nanfor/src/bytexor.prv $
*
* This is an original work by Forest Belt and is placed in the
* public domain.
*
* Modification history:
* ---------------------
*
* $Log: E:/nanfor/src/bytexor.prv $
*
* Rev 1.3 16 Aug 1991 19:35:48 GLENN
* Don Caton corrected some spelling errors in doc
*
* Rev 1.2 15 Aug 1991 23:03:10 GLENN
* Forest Belt proofread/edited/cleaned up doc
*
* Rev 1.1 14 Jun 1991 19:51:18 GLENN
* Minor edit to file header
*
* Rev 1.0 01 Apr 1991 01:00:58 GLENN
* Nanforum Toolkit
*
*/
/* $DOC$
* $FUNCNAME$
* FT_BYTEXOR()
* $CATEGORY$
* String
* $ONELINER$
* Perform bit-wise XOR on two ASCII characters (bytes)
* $SYNTAX$
* FT_BYTEXOR( <cByte1>, <cByte2> ) -> cNewByte
* $ARGUMENTS$
* <cByte1> and <cByte2> are characters from CHR(0) to CHR(255).
* May be passed in CHR() form, as character literals, or
* as expressions evaluating to CHR() values.
* $RETURNS$
* Returns resulting byte, in CHR() form. If parameters are faulty,
* returns NIL.
* $DESCRIPTION$
* Can be used for bit-wise byte manipulation. In effect, this is a
* bit-by-bit XOR operation. Equivalent to XOR assembler instruction.
*
* This function is presented to illustrate that bit-wise operations
* are possible with Clipper code. For greater speed, write .C or
* .ASM versions and use the Clipper Extend system.
* $EXAMPLES$
* This code performs a bit-wise XOR on two bytes represented
* by CHR(32) and CHR(55):
*
* cNewByte := FT_BYTEXOR( CHR(32), CHR(55) )
* ? ASC( cNewByte ) // result: 23
* ? cNewByte // result: non-printable character
*
* For a demonstration of Clipper bit manipulations, compile and
* link the program BITTEST.PRG in the Nanforum Toolkit source code.
* $SEEALSO$
* FT_BYTEOR() FT_BYTENOT() FT_BYTENEG() FT_BYTEAND()
* $END$
*/
FUNCTION FT_BYTEXOR(cByte1, cByte2)
LOCAL nCounter, cNewByte
IF valtype(cByte1) != "C" .or. valtype(cByte2) != "C" // parameter check
cNewByte := NIL
ELSE
cNewByte := chr(0)
FOR nCounter := 0 to 7 // test each bit position
IF FT_ISBIT(cByte1, nCounter) .or. FT_ISBIT(cByte2, nCounter)
IF .not. (FT_ISBIT(cByte1, nCounter) .and. FT_ISBIT(cByte2, nCounter))
cNewByte := FT_BITSET(cNewByte, nCounter)
ENDIF
ENDIF
NEXT
ENDIF
RETURN cNewByte