| 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: adler32.cc,v 1.1 2005/05/12 21:04:53 duns Exp $ */
|
|---|
| 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(uLong adler, const Bytef *buf, uInt len)
|
|---|
| 48 | {
|
|---|
| 49 | unsigned long s1 = adler & 0xffff;
|
|---|
| 50 | unsigned long s2 = (adler >> 16) & 0xffff;
|
|---|
| 51 | int k;
|
|---|
| 52 |
|
|---|
| 53 | if (buf == Z_NULL) return 1L;
|
|---|
| 54 |
|
|---|
| 55 | while (len > 0) {
|
|---|
| 56 | k = len < NMAX ? (int)len : NMAX;
|
|---|
| 57 | len -= k;
|
|---|
| 58 | while (k >= 16) {
|
|---|
| 59 | DO16(buf);
|
|---|
| 60 | buf += 16;
|
|---|
| 61 | k -= 16;
|
|---|
| 62 | }
|
|---|
| 63 | if (k != 0) do {
|
|---|
| 64 | s1 += *buf++;
|
|---|
| 65 | s2 += s1;
|
|---|
| 66 | } while (--k);
|
|---|
| 67 | MOD(s1);
|
|---|
| 68 | MOD(s2);
|
|---|
| 69 | }
|
|---|
| 70 | return (s2 << 16) | s1;
|
|---|
| 71 | }
|
|---|
