81 lines
2.4 KiB
Plaintext
81 lines
2.4 KiB
Plaintext
/*
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* File......: BYTEAND.PRG
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* Author....: Forest Belt, Computer Diagnostic Services, Inc.
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* CIS ID....: ?
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*
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* This is an original work by Forest Belt and is placed in the
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* public domain.
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*
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* Modification history:
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* ---------------------
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*
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* Rev 1.2 15 Aug 1991 23:03:02 GLENN
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* Forest Belt proofread/edited/cleaned up doc
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*
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* Rev 1.1 14 Jun 1991 19:51:12 GLENN
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* Minor edit to file header
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*
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* Rev 1.0 01 Apr 1991 01:00:50 GLENN
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* Nanforum Toolkit
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*
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*/
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/* $DOC$
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* $FUNCNAME$
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* FT_BYTEAND()
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* $CATEGORY$
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* String
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* $ONELINER$
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* Perform bit-wise AND on two ASCII characters (bytes)
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* $SYNTAX$
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* FT_BYTEAND( <cByte1>, <cByte2> ) -> cByte
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* $ARGUMENTS$
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* <cByte1> and <cByte2> are characters from CHR(0) TO CHR(255).
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* May be passed in CHR() form, as character literals, or as expressions
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* evaluating to CHR() values.
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* $RETURNS$
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* Returns resulting byte, in CHR() form. If parameters are faulty,
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* returns NIL.
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* $DESCRIPTION$
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* Can be used for any bit-wise masking operation. In effect, this is a
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* bit-by-bit AND operation. Equivalent to AND assembler instruction.
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*
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* This function is presented to illustrate that bit-wise operations
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* are possible with Clipper code. For greater speed, write .C or
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* .ASM versions and use the Clipper Extend system.
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* $EXAMPLES$
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* This code would mask out the high nibble (four most significant bits)
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* of the byte represented by chr(123) and leave the low nibble bits as in
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* the parameter byte.
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*
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* cNewbyte := FT_BYTEAND( CHR(123), CHR(15) )
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* ? asc(cNewByte) // result: 11
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* ? cNewByte // result: non-printable character
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*
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* For a demonstration of Clipper bit manipulations, compile and
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* link the program BITTEST.PRG in the Nanforum Toolkit source code.
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* $SEEALSO$
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* FT_BYTEOR() FT_BYTEXOR() FT_BYTENOT() FT_BYTENEG()
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* $END$
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*/
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FUNCTION FT_BYTEAND(cByte1, cByte2)
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LOCAL nCounter, cNewByte
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IF valtype(cByte1) != "C" .or. valtype(cByte2) != "C" // parameter check
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cNewByte := NIL
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ELSE
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cNewByte := chr(0)
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for nCounter := 0 to 7 // test each bit position
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if FT_ISBIT(cByte1, nCounter) .and. FT_ISBIT(cByte2, nCounter)
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cNewByte := FT_BITSET(cNewByte, nCounter)
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endif
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next
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ENDIF
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RETURN cNewByte
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