source: rtems/cpukit/zlib/adler32.c @ f369a50

4.11
Last change on this file since f369a50 was f369a50, checked in by Ralf Corsepius <ralf.corsepius@…>, on Mar 18, 2011 at 10:11:04 AM

Import from zlib-1.2.4

  • Property mode set to 100644
File size: 4.9 KB
Line 
1/* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2007 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6/* @(#) $Id$ */
7
8#include "zutil.h"
9
10#define local static
11
12local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
13
14#define BASE 65521UL    /* largest prime smaller than 65536 */
15#define NMAX 5552
16/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
17
18#define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
19#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
20#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
21#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
22#define DO16(buf)   DO8(buf,0); DO8(buf,8);
23
24/* use NO_DIVIDE if your processor does not do division in hardware */
25#ifdef NO_DIVIDE
26#  define MOD(a) \
27    do { \
28        if (a >= (BASE << 16)) a -= (BASE << 16); \
29        if (a >= (BASE << 15)) a -= (BASE << 15); \
30        if (a >= (BASE << 14)) a -= (BASE << 14); \
31        if (a >= (BASE << 13)) a -= (BASE << 13); \
32        if (a >= (BASE << 12)) a -= (BASE << 12); \
33        if (a >= (BASE << 11)) a -= (BASE << 11); \
34        if (a >= (BASE << 10)) a -= (BASE << 10); \
35        if (a >= (BASE << 9)) a -= (BASE << 9); \
36        if (a >= (BASE << 8)) a -= (BASE << 8); \
37        if (a >= (BASE << 7)) a -= (BASE << 7); \
38        if (a >= (BASE << 6)) a -= (BASE << 6); \
39        if (a >= (BASE << 5)) a -= (BASE << 5); \
40        if (a >= (BASE << 4)) a -= (BASE << 4); \
41        if (a >= (BASE << 3)) a -= (BASE << 3); \
42        if (a >= (BASE << 2)) a -= (BASE << 2); \
43        if (a >= (BASE << 1)) a -= (BASE << 1); \
44        if (a >= BASE) a -= BASE; \
45    } while (0)
46#  define MOD4(a) \
47    do { \
48        if (a >= (BASE << 4)) a -= (BASE << 4); \
49        if (a >= (BASE << 3)) a -= (BASE << 3); \
50        if (a >= (BASE << 2)) a -= (BASE << 2); \
51        if (a >= (BASE << 1)) a -= (BASE << 1); \
52        if (a >= BASE) a -= BASE; \
53    } while (0)
54#else
55#  define MOD(a) a %= BASE
56#  define MOD4(a) a %= BASE
57#endif
58
59/* ========================================================================= */
60uLong ZEXPORT adler32(adler, buf, len)
61    uLong adler;
62    const Bytef *buf;
63    uInt len;
64{
65    unsigned long sum2;
66    unsigned n;
67
68    /* split Adler-32 into component sums */
69    sum2 = (adler >> 16) & 0xffff;
70    adler &= 0xffff;
71
72    /* in case user likes doing a byte at a time, keep it fast */
73    if (len == 1) {
74        adler += buf[0];
75        if (adler >= BASE)
76            adler -= BASE;
77        sum2 += adler;
78        if (sum2 >= BASE)
79            sum2 -= BASE;
80        return adler | (sum2 << 16);
81    }
82
83    /* initial Adler-32 value (deferred check for len == 1 speed) */
84    if (buf == Z_NULL)
85        return 1L;
86
87    /* in case short lengths are provided, keep it somewhat fast */
88    if (len < 16) {
89        while (len--) {
90            adler += *buf++;
91            sum2 += adler;
92        }
93        if (adler >= BASE)
94            adler -= BASE;
95        MOD4(sum2);             /* only added so many BASE's */
96        return adler | (sum2 << 16);
97    }
98
99    /* do length NMAX blocks -- requires just one modulo operation */
100    while (len >= NMAX) {
101        len -= NMAX;
102        n = NMAX / 16;          /* NMAX is divisible by 16 */
103        do {
104            DO16(buf);          /* 16 sums unrolled */
105            buf += 16;
106        } while (--n);
107        MOD(adler);
108        MOD(sum2);
109    }
110
111    /* do remaining bytes (less than NMAX, still just one modulo) */
112    if (len) {                  /* avoid modulos if none remaining */
113        while (len >= 16) {
114            len -= 16;
115            DO16(buf);
116            buf += 16;
117        }
118        while (len--) {
119            adler += *buf++;
120            sum2 += adler;
121        }
122        MOD(adler);
123        MOD(sum2);
124    }
125
126    /* return recombined sums */
127    return adler | (sum2 << 16);
128}
129
130/* ========================================================================= */
131local uLong adler32_combine_(adler1, adler2, len2)
132    uLong adler1;
133    uLong adler2;
134    z_off64_t len2;
135{
136    unsigned long sum1;
137    unsigned long sum2;
138    unsigned rem;
139
140    /* the derivation of this formula is left as an exercise for the reader */
141    rem = (unsigned)(len2 % BASE);
142    sum1 = adler1 & 0xffff;
143    sum2 = rem * sum1;
144    MOD(sum2);
145    sum1 += (adler2 & 0xffff) + BASE - 1;
146    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
147    if (sum1 >= BASE) sum1 -= BASE;
148    if (sum1 >= BASE) sum1 -= BASE;
149    if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
150    if (sum2 >= BASE) sum2 -= BASE;
151    return sum1 | (sum2 << 16);
152}
153
154/* ========================================================================= */
155uLong ZEXPORT adler32_combine(adler1, adler2, len2)
156    uLong adler1;
157    uLong adler2;
158    z_off_t len2;
159{
160    return adler32_combine_(adler1, adler2, len2);
161}
162
163uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
164    uLong adler1;
165    uLong adler2;
166    z_off64_t len2;
167{
168    return adler32_combine_(adler1, adler2, len2);
169}
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