1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
9 #define BASE 65521L /* largest prime smaller than 65536 */
11 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13 #define DO1(buf) {s1 += *buf++; s2 += s1;}
14 #define DO2(buf) DO1(buf); DO1(buf);
15 #define DO4(buf) DO2(buf); DO2(buf);
16 #define DO8(buf) DO4(buf); DO4(buf);
17 #define DO16(buf) DO8(buf); DO8(buf);
19 unsigned long av_adler32_update(unsigned long adler, const uint8_t *buf, unsigned int len)
21 unsigned long s1 = adler & 0xffff;
22 unsigned long s2 = (adler >> 16) & 0xffff;
25 if (buf == NULL) return 1L;
28 k = len < NMAX ? len : NMAX;
40 return (s2 << 16) | s1;