/src/freetype/src/gzip/adler32.c

 1/* adler32.c -- compute the Adler-32 checksum of a data stream
 2 * Copyright (C) 1995-2002 Mark Adler
 3 * For conditions of distribution and use, see copyright notice in zlib.h
 4 */
 5
 6/* @(#) $Id$ */
 7
 8#include "zlib.h"
 9
10#define BASE 65521L /* largest prime smaller than 65536 */
11#define NMAX 5552
12/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13
14#define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
15#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
16#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
17#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
18#define DO16(buf)   DO8(buf,0); DO8(buf,8);
19
20/* ========================================================================= */
21ZEXPORT(uLong) adler32( /* adler, buf, len) */
22    uLong adler,
23    const Bytef *buf,
24    uInt len )
25{
26    unsigned long s1 = adler & 0xffff;
27    unsigned long s2 = (adler >> 16) & 0xffff;
28    int k;
29
30    if (buf == Z_NULL) return 1L;
31
32    while (len > 0) {
33        k = len < NMAX ? len : NMAX;
34        len -= k;
35        while (k >= 16) {
36            DO16(buf);
37            buf += 16;
38            k -= 16;
39        }
40        if (k != 0) do {
41            s1 += *buf++;
42            s2 += s1;
43        } while (--k);
44        s1 %= BASE;
45        s2 %= BASE;
46    }
47    return (s2 << 16) | s1;
48}