| John Criswell | 2a9d717 | 2004-02-06 16:36:42 +0000 | [diff] [blame] | 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 |
| 4 | */ |
| 5 | |
| 6 | /* @(#) $Id$ */ |
| 7 | |
| 8 | #define ZLIB_INTERNAL |
| 9 | #include "zlib.h" |
| 10 | |
| 11 | #define BASE 65521UL /* largest prime smaller than 65536 */ |
| 12 | #define NMAX 5552 |
| 13 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ |
| 14 | |
| 15 | #define DO1(buf,i) {s1 += buf[i]; s2 += s1;} |
| 16 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); |
| 17 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); |
| 18 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); |
| 19 | #define DO16(buf) DO8(buf,0); DO8(buf,8); |
| 20 | |
| 21 | #ifdef NO_DIVIDE |
| 22 | # define MOD(a) \ |
| 23 | do { \ |
| 24 | if (a >= (BASE << 16)) a -= (BASE << 16); \ |
| 25 | if (a >= (BASE << 15)) a -= (BASE << 15); \ |
| 26 | if (a >= (BASE << 14)) a -= (BASE << 14); \ |
| 27 | if (a >= (BASE << 13)) a -= (BASE << 13); \ |
| 28 | if (a >= (BASE << 12)) a -= (BASE << 12); \ |
| 29 | if (a >= (BASE << 11)) a -= (BASE << 11); \ |
| 30 | if (a >= (BASE << 10)) a -= (BASE << 10); \ |
| 31 | if (a >= (BASE << 9)) a -= (BASE << 9); \ |
| 32 | if (a >= (BASE << 8)) a -= (BASE << 8); \ |
| 33 | if (a >= (BASE << 7)) a -= (BASE << 7); \ |
| 34 | if (a >= (BASE << 6)) a -= (BASE << 6); \ |
| 35 | if (a >= (BASE << 5)) a -= (BASE << 5); \ |
| 36 | if (a >= (BASE << 4)) a -= (BASE << 4); \ |
| 37 | if (a >= (BASE << 3)) a -= (BASE << 3); \ |
| 38 | if (a >= (BASE << 2)) a -= (BASE << 2); \ |
| 39 | if (a >= (BASE << 1)) a -= (BASE << 1); \ |
| 40 | if (a >= BASE) a -= BASE; \ |
| 41 | } while (0) |
| 42 | #else |
| 43 | # define MOD(a) a %= BASE |
| 44 | #endif |
| 45 | |
| 46 | /* ========================================================================= */ |
| 47 | uLong ZEXPORT adler32(adler, buf, len) |
| 48 | uLong adler; |
| 49 | const Bytef *buf; |
| 50 | uInt len; |
| 51 | { |
| 52 | unsigned long s1 = adler & 0xffff; |
| 53 | unsigned long s2 = (adler >> 16) & 0xffff; |
| 54 | int k; |
| 55 | |
| 56 | if (buf == Z_NULL) return 1L; |
| 57 | |
| 58 | while (len > 0) { |
| 59 | k = len < NMAX ? (int)len : NMAX; |
| 60 | len -= k; |
| 61 | while (k >= 16) { |
| 62 | DO16(buf); |
| 63 | buf += 16; |
| 64 | k -= 16; |
| 65 | } |
| 66 | if (k != 0) do { |
| 67 | s1 += *buf++; |
| 68 | s2 += s1; |
| 69 | } while (--k); |
| 70 | MOD(s1); |
| 71 | MOD(s2); |
| 72 | } |
| 73 | return (s2 << 16) | s1; |
| 74 | } |