Bit Manipulation in FoxPro for Data Encryption
ID: Q98700
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The information in this article applies to:
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Microsoft Visual FoxPro for Windows, version 3.0
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Microsoft FoxPro for MS-DOS, versions 2.0, 2.5, 2.5a
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Microsoft FoxPro for Windows, versions 2.5, 2.5a
SUMMARY
Because FoxPro uses characters that have values between 0 and 255 (1 byte),
these character values and thus the bit pattern can be manipulated once the
characters are converted to numeric values using the ASC() command. This
sort of operation could be used for data encryption.
The program below illustrates how the bit pattern of an entire string can
be swapped by rotating the bit patterns of each character one at a time and
placing the resulting characters in reverse order in the output string.
MORE INFORMATION
*PROGRAM SHIFTSTR.PRG
* (RUN BY TYPING 'DO SHIFTSTR.PRG WITH <STRING>')
PARAMETERS A
?A
A=shift(A)
?A
PROCEDURE shift
PARAMETERS in_str
result=[]
SET DECIMAL TO 0
lngth=LEN(in_str)
DIMENSION out_array(lngth)
FOR char_num=1 TO lngth
x=ASC(SUBSTR(in_str,char_num,1))
y=0
FOR bit=7 TO 0 STEP -1
IF x>((2^bit)-1)
x=x-(2^bit)
y=y+(2^(7-bit))
ENDIF
ENDFOR
out_array(lngth-char_num+1)=CHR(y)
ENDFOR
FOR char_num=1 TO lngth
result=result+out_array(char_num)
ENDFOR
RETURN result
Additional query words:
VFoxWin FoxDos FoxWin encrypt password
Keywords : kbcode FxprgGeneral
Version : 2.00 2.50 2.50a | 2.50 2.50a 3.0
Platform : MS-DOS WINDOWS
Issue type :