src/lib/vampimg/ZLib/imadler.pas

   1 Unit imadler;
   2
   3 {
   4   adler32.c -- compute the Adler-32 checksum of a data stream
   5   Copyright (C) 1995-1998 Mark Adler
   6
   7   Pascal tranlastion
   8   Copyright (C) 1998 by Jacques Nomssi Nzali
   9   For conditions of distribution and use, see copyright notice in readme.txt
  10 }
  11
  12 interface
  13
  14 {$I imzconf.inc}
  15
  16 uses
  17   imzutil;
  18
  19 function adler32(adler : uLong; buf : pBytef; len : uInt) : uLong;
  20
  21 {    Update a running Adler-32 checksum with the bytes buf[0..len-1] and
  22    return the updated checksum. If buf is NIL, this function returns
  23    the required initial value for the checksum.
  24    An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
  25    much faster. Usage example:
  26
  27    var
  28      adler : uLong;
  29    begin
  30      adler := adler32(0, Z_NULL, 0);
  31
  32      while (read_buffer(buffer, length) <> EOF) do
  33        adler := adler32(adler, buffer, length);
  34
  35      if (adler <> original_adler) then
  36        error();
  37    end;
  38 }
  39
  40 implementation
  41
  42 const
  43   BASE = uLong(65521); { largest prime smaller than 65536 }
  44   {NMAX = 5552; original code with unsigned 32 bit integer }
  45   { NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 }
  46   NMAX = 3854;        { code with signed 32 bit integer }
  47   { NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^31-1 }
  48   { The penalty is the time loss in the extra MOD-calls. }
  49
  50
  51 { ========================================================================= }
  52
  53 function adler32(adler : uLong; buf : pBytef; len : uInt) : uLong;
  54 var
  55   s1, s2 : uLong;
  56   k : int;
  57 begin
  58   s1 := adler and $ffff;
  59   s2 := (adler shr 16) and $ffff;
  60
  61   if not Assigned(buf) then
  62   begin
  63     adler32 := uLong(1);
  64     exit;
  65   end;
  66
  67   while (len > 0) do
  68   begin
  69     if len < NMAX then
  70       k := len
  71     else
  72       k := NMAX;
  73     Dec(len, k);
  74     {
  75     while (k >= 16) do
  76     begin
  77       DO16(buf);
  78       Inc(buf, 16);
  79       Dec(k, 16);
  80     end;
  81     if (k <> 0) then
  82     repeat
  83       Inc(s1, buf^);
  84       Inc(puf);
  85       Inc(s2, s1);
  86       Dec(k);
  87     until (k = 0);
  88     }
  89     while (k > 0) do
  90     begin
  91       Inc(s1, buf^);
  92       Inc(s2, s1);
  93       Inc(buf);
  94       Dec(k);
  95     end;
  96     s1 := s1 mod BASE;
  97     s2 := s2 mod BASE;
  98   end;
  99   adler32 := (s2 shl 16) or s1;
 100 end;
 101
 102 {
 103 #define DO1(buf,i)
 104   begin
 105     Inc(s1, buf[i]);
 106     Inc(s2, s1);
 107   end;
 108 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
 109 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
 110 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
 111 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
 112 }
 113 end.