1/*
2 * Adler-32 checksum
3 *
4 * Copyright (c) 2003 by Joergen Ibsen / Jibz
5 * All Rights Reserved
6 *
7 * http://www.ibsensoftware.com/
8 *
9 * This software is provided 'as-is', without any express
10 * or implied warranty. In no event will the authors be
11 * held liable for any damages arising from the use of
12 * this software.
13 *
14 * Permission is granted to anyone to use this software
15 * for any purpose, including commercial applications,
16 * and to alter it and redistribute it freely, subject to
17 * the following restrictions:
18 *
19 * 1. The origin of this software must not be
20 * misrepresented; you must not claim that you
21 * wrote the original software. If you use this
22 * software in a product, an acknowledgment in
23 * the product documentation would be appreciated
24 * but is not required.
25 *
26 * 2. Altered source versions must be plainly marked
27 * as such, and must not be misrepresented as
28 * being the original software.
29 *
30 * 3. This notice may not be removed or altered from
31 * any source distribution.
32 */
33
34/*
35 * Adler-32 algorithm taken from the zlib source, which is
36 * Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
37 */
38
39#include "tinf.h"
40
41#define A32_BASE 65521
42#define A32_NMAX 5552
43
44uint32_t uzlib_adler32(const void *data, unsigned int length, uint32_t prev_sum /* 1 */)
45{
46 const unsigned char *buf = (const unsigned char *)data;
47
48 unsigned int s1 = prev_sum & 0xffff;
49 unsigned int s2 = prev_sum >> 16;
50
51 while (length > 0)
52 {
53 int k = length < A32_NMAX ? length : A32_NMAX;
54 int i;
55
56 for (i = k / 16; i; --i, buf += 16)
57 {
58 s1 += buf[0]; s2 += s1; s1 += buf[1]; s2 += s1;
59 s1 += buf[2]; s2 += s1; s1 += buf[3]; s2 += s1;
60 s1 += buf[4]; s2 += s1; s1 += buf[5]; s2 += s1;
61 s1 += buf[6]; s2 += s1; s1 += buf[7]; s2 += s1;
62
63 s1 += buf[8]; s2 += s1; s1 += buf[9]; s2 += s1;
64 s1 += buf[10]; s2 += s1; s1 += buf[11]; s2 += s1;
65 s1 += buf[12]; s2 += s1; s1 += buf[13]; s2 += s1;
66 s1 += buf[14]; s2 += s1; s1 += buf[15]; s2 += s1;
67 }
68
69 for (i = k % 16; i; --i) { s1 += *buf++; s2 += s1; }
70
71 s1 %= A32_BASE;
72 s2 %= A32_BASE;
73
74 length -= k;
75 }
76
77 return (s2 << 16) | s1;
78}
79