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96 lines
2.4 KiB
ObjectPascal
96 lines
2.4 KiB
ObjectPascal
{
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Copyright (c) 2000-2002 by Free Pascal Development Team
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Routines to compute CRC values
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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****************************************************************************
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}
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Unit fpccrc;
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{$i fpcdefs.inc}
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Interface
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Function UpdateCrc32(InitCrc:cardinal;const InBuf;InLen:integer):cardinal;
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{ If needed trims the string to maxlen, adding at the end the CRC32 of discarded chars.
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The resulting string is guaranteed to be not longer than maxlen. }
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function TrimStrCRC32(const s: ansistring; maxlen: longint): ansistring;
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Implementation
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{*****************************************************************************
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Crc 32
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*****************************************************************************}
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var
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Crc32Tbl : array[0..255] of cardinal;
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procedure MakeCRC32Tbl;
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var
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crc : cardinal;
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i,n : integer;
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begin
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for i:=0 to 255 do
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begin
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crc:=i;
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for n:=1 to 8 do
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if (crc and 1)<>0 then
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crc:=(crc shr 1) xor cardinal($edb88320)
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else
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crc:=crc shr 1;
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Crc32Tbl[i]:=crc;
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end;
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end;
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Function UpdateCrc32(InitCrc:cardinal;const InBuf;InLen:Integer):cardinal;
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var
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i : integer;
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p : pchar;
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begin
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if Crc32Tbl[1]=0 then
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MakeCrc32Tbl;
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p:=@InBuf;
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result:=not InitCrc;
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for i:=1 to InLen do
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begin
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result:=Crc32Tbl[byte(result) xor byte(p^)] xor (result shr 8);
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inc(p);
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end;
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result:=not result;
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end;
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function TrimStrCRC32(const s: ansistring; maxlen: longint): ansistring;
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var
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crc: DWord;
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len: longint;
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begin
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len:=length(s);
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if (len<=maxlen) or (len<12) then
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result:=s
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else
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begin
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dec(maxlen,11);
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crc:=0;
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crc:=UpdateCrc32(crc,s[maxlen+1],len-maxlen);
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result:=copy(s,1,maxlen)+'$CRC'+hexstr(crc,8);
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end;
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end;
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end.
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