hedgewars/adler32.pas
author nemo
Thu, 07 Apr 2011 11:30:56 -0400
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unit Adler32;
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{ZLib - Adler32 checksum function}
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interface
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(*************************************************************************
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 DESCRIPTION     :  ZLib - Adler32 checksum function
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 REQUIREMENTS    :  TP5-7, D1-D7/D9-D10/D12, FPC, VP
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 EXTERNAL DATA   :  ---
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 MEMORY USAGE    :  ---
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 DISPLAY MODE    :  ---
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 REFERENCES      :  RFC 1950 (http://tools.ietf.org/html/rfc1950)
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 Version  Date      Author      Modification
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 -------  --------  -------     ------------------------------------------
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 0.10     30.08.03  W.Ehrhardt  Initial version based on MD5 layout
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 2.10     30.08.03  we          Common vers., XL versions for Win32
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 2.20     27.09.03  we          FPC/go32v2
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 2.30     05.10.03  we          STD.INC, TP5.0
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 2.40     10.10.03  we          common version, english comments
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 3.00     01.12.03  we          Common version 3.0
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 3.01     22.05.05  we          Adler32UpdateXL (i,n: integer)
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 3.02     17.12.05  we          Force $I- in Adler32File
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 3.03     07.08.06  we          $ifdef BIT32: (const fname: shortstring...)
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 3.04     10.02.07  we          Adler32File: no eof, XL and filemode via $ifdef
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 3.05     04.07.07  we          BASM16: speed-up factor 15
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 3.06     12.11.08  we          uses BTypes, Ptr2Inc and/or Str255
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 3.07     25.04.09  we          updated RFC URL(s)
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 3.08     19.07.09  we          D12 fix: assign with typecast string(fname)
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**************************************************************************)
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(*-------------------------------------------------------------------------
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 (C) Copyright 2002-2009 Wolfgang Ehrhardt
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 This software is provided 'as-is', without any express or implied warranty.
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 In no event will the authors be held liable for any damages arising from
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 the use of this software.
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 Permission is granted to anyone to use this software for any purpose,
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 including commercial applications, and to alter it and redistribute it
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 freely, subject to the following restrictions:
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 1. The origin of this software must not be misrepresented; you must not
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    claim that you wrote the original software. If you use this software in
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    a product, an acknowledgment in the product documentation would be
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    appreciated but is not required.
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 2. Altered source versions must be plainly marked as such, and must not be
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    misrepresented as being the original software.
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 3. This notice may not be removed or altered from any source distribution.
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----------------------------------------------------------------------------*)
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(*
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As per the license above, noting that this implementation of adler32 was stripped of everything we didn't need.
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That means no btypes, file loading, and the assembly version disabled.
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*)
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procedure Adler32Update(var adler: longint; Msg: pointer; Len: longint);
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implementation
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(*
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$ifdef BASM16
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procedure Adler32Update(var adler: longint; Msg: pointer; Len: longint);
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  //-update Adler32 with Msg data
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const
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  BASE = 65521; // max. prime < 65536
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  NMAX =  5552; // max. n with 255n(n+1)/2 + (n+1)(BASE-1) < 2^32
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type
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  LH    = packed record
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            L,H: word;
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          end;
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var
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  s1,s2: longint;
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  n: integer;
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begin
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  s1 := LH(adler).L;
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  s2 := LH(adler).H;
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  while Len > 0 do begin
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    if Len<NMAX then n := Len else n := NMAX;
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    //BASM increases speed from about 52 cyc/byte to about 3.7 cyc/byte
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    asm
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                    mov  cx,[n]
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            db $66; mov  ax,word ptr [s1]
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            db $66; mov  di,word ptr [s2]
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                    les  si,[msg]
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      @@1:  db $66, $26, $0f, $b6, $1c      // movzx ebx,es:[si]
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                    inc  si
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            db $66; add  ax,bx              // inc(s1, pByte(Msg)^)
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            db $66; add  di,ax              // inc(s2, s1
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                    dec  cx
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                    jnz  @@1
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            db $66; sub  cx,cx
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                    mov  cx,BASE
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            db $66; sub  dx,dx
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            db $66; div  cx
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            db $66; mov  word ptr [s1],dx   // s1 := s1 mod BASE
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            db $66; sub  dx,dx
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            db $66; mov  ax,di
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            db $66; div  cx
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            db $66; mov  word ptr [s2],dx   // s2 := s2 mod BASE
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                    mov  word ptr [msg],si  // save offset for next chunk
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    end;
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    dec(len, n);
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  end;
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  LH(adler).L := word(s1);
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  LH(adler).H := word(s2);
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end;
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*)
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procedure Adler32Update(var adler: longint; Msg: pointer; Len: longint);
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  {-update Adler32 with Msg data}
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const
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  BASE = 65521; {max. prime < 65536 }
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  NMAX =  3854; {max. n with 255n(n+1)/2 + (n+1)(BASE-1) < 2^31}
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type
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  LH    = packed record
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            L,H: word;
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          end;
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var
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  s1,s2: longint;
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  i,n: integer;
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begin
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  s1 := LH(adler).L;
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  s2 := LH(adler).H;
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  while Len > 0 do begin
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    if Len<NMAX then n := Len else n := NMAX;
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    for i:=1 to n do begin
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      inc(s1, pByte(Msg)^);
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      inc(Msg);
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      inc(s2, s1);
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    end;
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    s1 := s1 mod BASE;
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    s2 := s2 mod BASE;
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    dec(len, n);
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  end;
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  LH(adler).L := word(s1);
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  LH(adler).H := word(s2);
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end;
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end.