CRC

 BBS: Inland Empire Archive
Date: 03-06-93 (23:46)             Number: 359
From: CORIDON HENSHAW              Refer#: NONE
  To: CABELL CLARKE                 Recvd: NO  
Subj: CRC                            Conf: (2) Quik_Bas

Hello Cabell!

Friday March 05 1993, Cabell Clarke writes to All:

 CC> Does anyone have or know of a routine to compute a crc
 CC> 32 from a string?  I
 CC> am in dire need of such as beast and would kill to get my hands on one.

Here's some BASIC source for CRC32 and CRC26.  I also have
a ASM version of the CRC32 code, if you want it.

=== BEGIN ===
DECLARE FUNCTION CRC16& (Block$)
DECLARE FUNCTION CRC32& (Block$)

DEFINT A-Z
FUNCTION CRC16& (B$)      'Calculates CRC for Each Block

DIM Power(0 TO 7)                              'For the 8 Powers of 2
DIM CRC AS LONG

FOR I = 0 TO 7                                 'Calculate Once Per Block to
   Power(I) = 2 ^ I                            ' Increase Speed Within FOR J
NEXT I                                         ' Loop
CRC = 0                                        'Reset for Each Text Block
FOR I = 1 TO LEN(B$)                           'Calculate for Length of Block
   ByteVal = ASC(MID$(B$, I, 1))
   FOR J = 7 TO 0 STEP -1
      TestBit = ((CRC AND 32768) = 32768) XOR ((ByteVal AND
Power(J)) = _ Power(J))
      CRC = ((CRC AND 32767&) * 2&)
      IF TestBit THEN CRC = CRC XOR &H1021&     ' <-- This for 16 Bit CRC
   NEXT J
NEXT I
CRC16& = CRC                               'Return the Word Value
END FUNCTION


DEFSNG A-Z
FUNCTION CRC32& (B$)      'Calculates CRC for Each Block

DIM Power(0 TO 7)                              'For the 8 Powers of 2
DIM CRC AS LONG

FOR I = 0 TO 7                                 'Calculate Once Per Block to
   Power(I) = 2 ^ I                            ' Increase Speed Within FOR J
NEXT I                                         ' Loop
CRC = 0                                        'Reset for Each Text Block
FOR I = 1 TO LEN(B$)                           'Calculate for Length of Block
   ByteVal = ASC(MID$(B$, I, 1))
   FOR J = 7 TO 0 STEP -1
      TestBit = ((CRC AND 32768) = 32768) XOR ((ByteVal AND
Power(J)) =_ Power(J))
      CRC = ((CRC AND 32767&) * 2&)
      IF TestBit THEN CRC = CRC XOR &H8005&     ' <-- This for 32 Bit CRC
   NEXT J
NEXT I
CRC32& = CRC                               'Return the Word Value
END FUNCTION
=== END ===

Coridon Henshaw / Sirrus Software / QBCIMR FTSC Standards Technician / SM DEV

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