1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2003 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
12 #define BASE 65521UL /* largest prime smaller than 65536 */
14 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
16 #define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
17 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
18 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
19 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
20 #define DO16(buf) DO8(buf,0); DO8(buf,8);
25 if (a >= (BASE << 16)) a -= (BASE << 16); \
26 if (a >= (BASE << 15)) a -= (BASE << 15); \
27 if (a >= (BASE << 14)) a -= (BASE << 14); \
28 if (a >= (BASE << 13)) a -= (BASE << 13); \
29 if (a >= (BASE << 12)) a -= (BASE << 12); \
30 if (a >= (BASE << 11)) a -= (BASE << 11); \
31 if (a >= (BASE << 10)) a -= (BASE << 10); \
32 if (a >= (BASE << 9)) a -= (BASE << 9); \
33 if (a >= (BASE << 8)) a -= (BASE << 8); \
34 if (a >= (BASE << 7)) a -= (BASE << 7); \
35 if (a >= (BASE << 6)) a -= (BASE << 6); \
36 if (a >= (BASE << 5)) a -= (BASE << 5); \
37 if (a >= (BASE << 4)) a -= (BASE << 4); \
38 if (a >= (BASE << 3)) a -= (BASE << 3); \
39 if (a >= (BASE << 2)) a -= (BASE << 2); \
40 if (a >= (BASE << 1)) a -= (BASE << 1); \
41 if (a >= BASE) a -= BASE; \
44 # define MOD(a) a %= BASE
47 /* ========================================================================= */
48 uLong ZEXPORT adler32(adler, buf, len)
53 unsigned long s1 = adler & 0xffff;
54 unsigned long s2 = (adler >> 16) & 0xffff;
57 if (buf == Z_NULL) return 1L;
60 k = len < NMAX ? (int)len : NMAX;
74 return (s2 << 16) | s1;