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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;
{$i fpcdefs.inc}
Interface
Function UpdateCrc32(InitCrc:cardinal;const InBuf;InLen:integer):cardinal;
{ If needed trims the string to maxlen, adding at the end the CRC32 of discarded chars.
The resulting string is guaranteed to be not longer than maxlen. }
function TrimStrCRC32(const s: ansistring; maxlen: longint): ansistring;
Implementation
{*****************************************************************************
Crc 32
*****************************************************************************}
var
Crc32Tbl : array[0..255] of cardinal;
procedure MakeCRC32Tbl;
var
crc : cardinal;
i,n : integer;
begin
for i:=0 to 255 do
begin
crc:=i;
for n:=1 to 8 do
if (crc and 1)<>0 then
crc:=(crc shr 1) xor cardinal($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;
function TrimStrCRC32(const s: ansistring; maxlen: longint): ansistring;
var
crc: DWord;
len: longint;
begin
len:=length(s);
if (len<=maxlen) or (len<12) then
result:=s
else
begin
dec(maxlen,11);
crc:=0;
crc:=UpdateCrc32(crc,s[maxlen+1],len-maxlen);
result:=copy(s,1,maxlen)+'$CRC'+hexstr(crc,8);
end;
end;
end.
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