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- {
- Copyright (c) 2000-2002 by Free Pascal Development Team
- Routines to compute CRC values
- This program is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
- (at your option) any later version.
- This program is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- GNU General Public License for more details.
- You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software
- Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- ****************************************************************************
- }
- Unit fpccrc;
- {$i fpcdefs.inc}
- Interface
- Function UpdateCrc32(InitCrc:cardinal;const InBuf;InLen:integer):cardinal;
- Implementation
- {*****************************************************************************
- Crc 32
- *****************************************************************************}
- var
- Crc32Tbl : array[0..255] of cardinal;
- procedure MakeCRC32Tbl;
- var
- crc : cardinal;
- i,n : integer;
- begin
- for i:=0 to 255 do
- begin
- crc:=i;
- for n:=1 to 8 do
- if (crc and 1)<>0 then
- crc:=(crc shr 1) xor cardinal($edb88320)
- else
- crc:=crc shr 1;
- Crc32Tbl[i]:=crc;
- end;
- end;
- Function UpdateCrc32(InitCrc:cardinal;const InBuf;InLen:Integer):cardinal;
- var
- i : integer;
- p : pchar;
- begin
- if Crc32Tbl[1]=0 then
- MakeCrc32Tbl;
- p:=@InBuf;
- result:=not InitCrc;
- for i:=1 to InLen do
- begin
- result:=Crc32Tbl[byte(result) xor byte(p^)] xor (result shr 8);
- inc(p);
- end;
- result:=not result;
- end;
- end.
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