{
    $Id: crc.pas,v 1.1 2000/07/13 06:29:48 michael Exp $
    Copyright (c) 2000 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 CRC;

Interface
Function Crc32(Const HStr:String):longint;
Function UpdateCrc32(InitCrc:longint;var InBuf;InLen:Longint):longint;
Function UpdCrc32(InitCrc:longint;b:byte):longint;


Implementation

{*****************************************************************************
                                   Crc 32
*****************************************************************************}

var
  Crc32Tbl : array[0..255] of longint;

procedure MakeCRC32Tbl;
var
  crc : longint;
  i,n : byte;
begin
  for i:=0 to 255 do
   begin
     crc:=i;
     for n:=1 to 8 do
      if odd(crc) then
       crc:=(crc shr 1) xor longint($edb88320)
      else
       crc:=crc shr 1;
     Crc32Tbl[i]:=crc;
   end;
end;


{$ifopt R+}
{$define Range_check_on}
{$endif opt R+}

{$R- needed here }
{CRC 32}
Function Crc32(Const HStr:String):longint;
var
  i,InitCrc : longint;
begin
  if Crc32Tbl[1]=0 then
   MakeCrc32Tbl;
  InitCrc:=longint($ffffffff);
  for i:=1 to Length(Hstr) do
   InitCrc:=Crc32Tbl[byte(InitCrc) xor ord(Hstr[i])] xor (InitCrc shr 8);
  Crc32:=InitCrc;
end;



Function UpdateCrc32(InitCrc:longint;var InBuf;InLen:Longint):longint;
var
  i : word;
  p : pchar;
begin
  if Crc32Tbl[1]=0 then
   MakeCrc32Tbl;
  p:=@InBuf;
  for i:=1 to InLen do
   begin
     InitCrc:=Crc32Tbl[byte(InitCrc) xor byte(p^)] xor (InitCrc shr 8);
     inc(longint(p));
   end;
  UpdateCrc32:=InitCrc;
end;



Function UpdCrc32(InitCrc:longint;b:byte):longint;
begin
  if Crc32Tbl[1]=0 then
   MakeCrc32Tbl;
  UpdCrc32:=Crc32Tbl[byte(InitCrc) xor b] xor (InitCrc shr 8);
end;

{$ifdef Range_check_on}
{$R+}
{$undef Range_check_on}
{$endif Range_check_on}

end.