1/*
2 * Copyright (c) 2008 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
24 * limitations under the License.
25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28/* adler32.c -- compute the Adler-32 checksum of a data stream
29 * Copyright (C) 1995-2004 Mark Adler
30 * For conditions of distribution and use, see copyright notice in zlib.h
31 */
32
33/* @(#) $Id$ */
34
35
36#define ZLIB_INTERNAL
37#if KERNEL
38    #include <libkern/zlib.h>
39#else
40    #include "zlib.h"
41#endif /* KERNEL */
42
43
44#define BASE 65521UL    /* largest prime smaller than 65536 */
45#define NMAX 5552
46/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
47
48#define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
49#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
50#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
51#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
52#define DO16(buf)   DO8(buf,0); DO8(buf,8);
53
54/* use NO_DIVIDE if your processor does not do division in hardware */
55#ifdef NO_DIVIDE
56#  define MOD(a) \
57    do { \
58        if (a >= (BASE << 16)) a -= (BASE << 16); \
59        if (a >= (BASE << 15)) a -= (BASE << 15); \
60        if (a >= (BASE << 14)) a -= (BASE << 14); \
61        if (a >= (BASE << 13)) a -= (BASE << 13); \
62        if (a >= (BASE << 12)) a -= (BASE << 12); \
63        if (a >= (BASE << 11)) a -= (BASE << 11); \
64        if (a >= (BASE << 10)) a -= (BASE << 10); \
65        if (a >= (BASE << 9)) a -= (BASE << 9); \
66        if (a >= (BASE << 8)) a -= (BASE << 8); \
67        if (a >= (BASE << 7)) a -= (BASE << 7); \
68        if (a >= (BASE << 6)) a -= (BASE << 6); \
69        if (a >= (BASE << 5)) a -= (BASE << 5); \
70        if (a >= (BASE << 4)) a -= (BASE << 4); \
71        if (a >= (BASE << 3)) a -= (BASE << 3); \
72        if (a >= (BASE << 2)) a -= (BASE << 2); \
73        if (a >= (BASE << 1)) a -= (BASE << 1); \
74        if (a >= BASE) a -= BASE; \
75    } while (0)
76#  define MOD4(a) \
77    do { \
78        if (a >= (BASE << 4)) a -= (BASE << 4); \
79        if (a >= (BASE << 3)) a -= (BASE << 3); \
80        if (a >= (BASE << 2)) a -= (BASE << 2); \
81        if (a >= (BASE << 1)) a -= (BASE << 1); \
82        if (a >= BASE) a -= BASE; \
83    } while (0)
84#else
85#  define MOD(a) a %= BASE
86#  define MOD4(a) a %= BASE
87#endif
88
89/* ========================================================================= */
90uLong ZEXPORT adler32(adler, buf, len)
91    uLong adler;
92    const Bytef *buf;
93    uInt len;
94{
95    unsigned long sum2;
96    unsigned n;
97
98    /* split Adler-32 into component sums */
99    sum2 = (adler >> 16) & 0xffff;
100    adler &= 0xffff;
101
102    /* in case user likes doing a byte at a time, keep it fast */
103    if (len == 1) {
104        adler += buf[0];
105        if (adler >= BASE)
106            adler -= BASE;
107        sum2 += adler;
108        if (sum2 >= BASE)
109            sum2 -= BASE;
110        return adler | (sum2 << 16);
111    }
112
113    /* initial Adler-32 value (deferred check for len == 1 speed) */
114    if (buf == Z_NULL)
115        return 1L;
116
117    /* in case short lengths are provided, keep it somewhat fast */
118    if (len < 16) {
119        while (len--) {
120            adler += *buf++;
121            sum2 += adler;
122        }
123        if (adler >= BASE)
124            adler -= BASE;
125        MOD4(sum2);             /* only added so many BASE's */
126        return adler | (sum2 << 16);
127    }
128
129
130    /* do length NMAX blocks -- requires just one modulo operation */
131    while (len >= NMAX) {
132        len -= NMAX;
133        n = NMAX / 16;          /* NMAX is divisible by 16 */
134        do {
135            DO16(buf);          /* 16 sums unrolled */
136            buf += 16;
137        } while (--n);
138        MOD(adler);
139        MOD(sum2);
140    }
141
142    /* do remaining bytes (less than NMAX, still just one modulo) */
143    if (len) {                  /* avoid modulos if none remaining */
144        while (len >= 16) {
145            len -= 16;
146            DO16(buf);
147            buf += 16;
148        }
149        while (len--) {
150            adler += *buf++;
151            sum2 += adler;
152        }
153        MOD(adler);
154        MOD(sum2);
155    }
156
157    /* return recombined sums */
158    return adler | (sum2 << 16);
159}
160
161/* ========================================================================= */
162uLong ZEXPORT adler32_combine(adler1, adler2, len2)
163    uLong adler1;
164    uLong adler2;
165    z_off_t len2;
166{
167    unsigned long sum1;
168    unsigned long sum2;
169    unsigned rem;
170
171    /* the derivation of this formula is left as an exercise for the reader */
172    rem = (unsigned)(len2 % BASE);
173    sum1 = adler1 & 0xffff;
174    sum2 = rem * sum1;
175    MOD(sum2);
176    sum1 += (adler2 & 0xffff) + BASE - 1;
177    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
178    if (sum1 > BASE) sum1 -= BASE;
179    if (sum1 > BASE) sum1 -= BASE;
180    if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
181    if (sum2 > BASE) sum2 -= BASE;
182    return sum1 | (sum2 << 16);
183}
184