| 1 | /* adler32.c -- compute the Adler-32 checksum of a data stream |
| 2 | * Copyright (C) 1995-1998 Mark Adler |
| 3 | * For conditions of distribution and use, see copyright notice in zlib.h |
| 4 | */ |
| 5 | |
| 6 | /* @(#) $Id$ */ |
| 7 | |
| 8 | #include "../zlib/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 | /* ========================================================================= */ |
| 21 | #if defined(__VISAGECPP__) /* Visualage can't handle this antiquated interface */ |
| 22 | uLong ZEXPORT adler32 (uLong adler, const Bytef* buf, uInt len) |
| 23 | #else |
| 24 | uLong ZEXPORT adler32(adler, buf, len) |
| 25 | uLong adler; |
| 26 | const Bytef *buf; |
| 27 | uInt len; |
| 28 | #endif |
| 29 | { |
| 30 | unsigned long s1 = adler & 0xffff; |
| 31 | unsigned long s2 = (adler >> 16) & 0xffff; |
| 32 | int k; |
| 33 | |
| 34 | if (buf == Z_NULL) return 1L; |
| 35 | |
| 36 | while (len > 0) { |
| 37 | k = len < NMAX ? len : NMAX; |
| 38 | len -= k; |
| 39 | while (k >= 16) { |
| 40 | DO16(buf); |
| 41 | buf += 16; |
| 42 | k -= 16; |
| 43 | } |
| 44 | if (k != 0) do { |
| 45 | s1 += *buf++; |
| 46 | s2 += s1; |
| 47 | } while (--k); |
| 48 | s1 %= BASE; |
| 49 | s2 %= BASE; |
| 50 | } |
| 51 | return (s2 << 16) | s1; |
| 52 | } |