88 lines
2.8 KiB
Plaintext
88 lines
2.8 KiB
Plaintext
{
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$Project$
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$Workfile$
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$Revision$
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$DateUTC$
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$Id$
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This file is part of the Indy (Internet Direct) project, and is offered
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under the dual-licensing agreement described on the Indy website.
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(http://www.indyproject.org/)
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Copyright:
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(c) 1993-2005, Chad Z. Hower and the Indy Pit Crew. All rights reserved.
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}
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{
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$Log$
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}
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{
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Rev 1.0 11/13/2002 08:30:30 AM JPMugaas
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Initial import from FTP VC.
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}
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{*===========================================================================*}
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{* DESCRIPTION *}
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{*****************************************************************************}
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{* PROJECT : Indy 10 *}
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{* AUTHOR : Bas Gooijen *}
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{* MAINTAINER : Bas Gooijen *}
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{*...........................................................................*}
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{* DESCRIPTION *}
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{* *}
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{* Implementation of the Adler 32 hash algoritm *}
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{* Adler 32 is almost as reliable as CRC32, but faster *}
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{* *}
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{*...........................................................................*}
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{* HISTORY *}
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{* DATE VERSION AUTHOR REASONS *}
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{* *}
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{* 17/10/2002 1.0 Bas Gooijen Initial start *}
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{*****************************************************************************}
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unit IdHashAdler32;
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interface
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{$i IdCompilerDefines.inc}
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uses
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IdHash;
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type
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TIdHashAdler32 = class(TIdHash32)
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public
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procedure HashStart(var VRunningHash : LongWord); override;
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procedure HashByte(var VRunningHash : LongWord; const AByte : Byte); override;
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end;
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implementation
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const
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BASE = 65521; { largest prime smaller than 65536 }
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NMAX = 5552; { NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 }
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{ TIdHashAdler32 }
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procedure TIdHashAdler32.HashStart(var VRunningHash : LongWord);
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begin
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VRunningHash := 1;
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end;
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procedure TIdHashAdler32.HashByte(var VRunningHash : LongWord; const AByte : Byte);
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var
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s1, s2: LongWord;
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begin
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s1 := VRunningHash and $FFFF;
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s2 := (VRunningHash shr 16) and $FFFF;
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Inc(s1, AByte);
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Inc(s2, s1);
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s1 := s1 mod BASE;
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s2 := s2 mod BASE;
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VRunningHash := (s2 shl 16) or s1;
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end;
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end.
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