source: rtems/cpukit/zlib/adler32.c @ 959f7df2

4.104.114.84.9
Last change on this file since 959f7df2 was 959f7df2, checked in by Ralf Corsepius <ralf.corsepius@…>, on Oct 28, 2005 at 7:22:42 AM

Import of zlib-1.2.2.2.tar.gz

  • Property mode set to 100644
File size: 4.5 KB
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1/* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2004 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)  {adler += (buf)[i]; sum2 += adler;}
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/* use NO_DIVIDE if your processor does not do division in hardware */
22#ifdef NO_DIVIDE
23#  define MOD(a) \
24    do { \
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; \
42    } while (0)
43#  define MOD4(a) \
44    do { \
45        if (a >= (BASE << 4)) a -= (BASE << 4); \
46        if (a >= (BASE << 3)) a -= (BASE << 3); \
47        if (a >= (BASE << 2)) a -= (BASE << 2); \
48        if (a >= (BASE << 1)) a -= (BASE << 1); \
49        if (a >= BASE) a -= BASE; \
50    } while (0)
51#else
52#  define MOD(a) a %= BASE
53#  define MOD4(a) a %= BASE
54#endif
55
56/* ========================================================================= */
57uLong ZEXPORT adler32(adler, buf, len)
58    uLong adler;
59    const Bytef *buf;
60    uInt len;
61{
62    unsigned long sum2;
63    unsigned n;
64
65    /* split Adler-32 into component sums */
66    sum2 = (adler >> 16) & 0xffff;
67    adler &= 0xffff;
68
69    /* in case user likes doing a byte at a time, keep it fast */
70    if (len == 1) {
71        adler += buf[0];
72        if (adler >= BASE)
73            adler -= BASE;
74        sum2 += adler;
75        if (sum2 >= BASE)
76            sum2 -= BASE;
77        return adler | (sum2 << 16);
78    }
79
80    /* initial Adler-32 value (deferred check for len == 1 speed) */
81    if (buf == Z_NULL)
82        return 1L;
83
84    /* in case short lengths are provided, keep it somewhat fast */
85    if (len < 16) {
86        while (len--) {
87            adler += *buf++;
88            sum2 += adler;
89        }
90        if (adler >= BASE)
91            adler -= BASE;
92        MOD4(sum2);             /* only added so many BASE's */
93        return adler | (sum2 << 16);
94    }
95
96    /* do length NMAX blocks -- requires just one modulo operation */
97    while (len >= NMAX) {
98        len -= NMAX;
99        n = NMAX / 16;          /* NMAX is divisible by 16 */
100        do {
101            DO16(buf);          /* 16 sums unrolled */
102            buf += 16;
103        } while (--n);
104        MOD(adler);
105        MOD(sum2);
106    }
107
108    /* do remaining bytes (less than NMAX, still just one modulo) */
109    if (len) {                  /* avoid modulos if none remaining */
110        while (len >= 16) {
111            len -= 16;
112            DO16(buf);
113            buf += 16;
114        }
115        while (len--) {
116            adler += *buf++;
117            sum2 += adler;
118        }
119        MOD(adler);
120        MOD(sum2);
121    }
122
123    /* return recombined sums */
124    return adler | (sum2 << 16);
125}
126
127/* ========================================================================= */
128uLong ZEXPORT adler32_combine(adler1, adler2, len2)
129    uLong adler1;
130    uLong adler2;
131    z_off_t len2;
132{
133    unsigned long sum1;
134    unsigned long sum2;
135    unsigned rem;
136
137    /* the derivation of this formula is left as an exercise for the reader */
138    rem = (unsigned)(len2 % BASE);
139    sum1 = adler1 & 0xffff;
140    sum2 = rem * sum1;
141    MOD(sum2);
142    sum1 += (adler2 & 0xffff) + BASE - 1;
143    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
144    if (sum1 > BASE) sum1 -= BASE;
145    if (sum1 > BASE) sum1 -= BASE;
146    if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
147    if (sum2 > BASE) sum2 -= BASE;
148    return sum1 | (sum2 << 16);
149}
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