1 /*
2 * Copyright (c) 2008-2016 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 /* ========================================================================= */
90 uLong ZEXPORT
adler32(uLong adler,const Bytef * buf,uInt len)91 adler32(uLong adler, const Bytef *buf, uInt len)
92 {
93 unsigned long sum2;
94 unsigned n;
95
96 /* split Adler-32 into component sums */
97 sum2 = (adler >> 16) & 0xffff;
98 adler &= 0xffff;
99
100 /* in case user likes doing a byte at a time, keep it fast */
101 if (len == 1) {
102 adler += buf[0];
103 if (adler >= BASE)
104 adler -= BASE;
105 sum2 += adler;
106 if (sum2 >= BASE)
107 sum2 -= BASE;
108 return adler | (sum2 << 16);
109 }
110
111 /* initial Adler-32 value (deferred check for len == 1 speed) */
112 if (buf == Z_NULL)
113 return 1L;
114
115 /* in case short lengths are provided, keep it somewhat fast */
116 if (len < 16) {
117 while (len--) {
118 adler += *buf++;
119 sum2 += adler;
120 }
121 if (adler >= BASE)
122 adler -= BASE;
123 MOD4(sum2); /* only added so many BASE's */
124 return adler | (sum2 << 16);
125 }
126
127
128 /* do length NMAX blocks -- requires just one modulo operation */
129 while (len >= NMAX) {
130 len -= NMAX;
131 n = NMAX / 16; /* NMAX is divisible by 16 */
132 do {
133 DO16(buf); /* 16 sums unrolled */
134 buf += 16;
135 } while (--n);
136 MOD(adler);
137 MOD(sum2);
138 }
139
140 /* do remaining bytes (less than NMAX, still just one modulo) */
141 if (len) { /* avoid modulos if none remaining */
142 while (len >= 16) {
143 len -= 16;
144 DO16(buf);
145 buf += 16;
146 }
147 while (len--) {
148 adler += *buf++;
149 sum2 += adler;
150 }
151 MOD(adler);
152 MOD(sum2);
153 }
154
155 /* return recombined sums */
156 return adler | (sum2 << 16);
157 }
158
159 /* ========================================================================= */
160 uLong ZEXPORT
adler32_combine(uLong adler1,uLong adler2,z_off_t len2)161 adler32_combine(uLong adler1, uLong adler2, z_off_t len2)
162 {
163 unsigned long sum1;
164 unsigned long sum2;
165 unsigned rem;
166
167 /* the derivation of this formula is left as an exercise for the reader */
168 rem = (unsigned)(len2 % BASE);
169 sum1 = adler1 & 0xffff;
170 sum2 = rem * sum1;
171 MOD(sum2);
172 sum1 += (adler2 & 0xffff) + BASE - 1;
173 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
174 if (sum1 > BASE) sum1 -= BASE;
175 if (sum1 > BASE) sum1 -= BASE;
176 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
177 if (sum2 > BASE) sum2 -= BASE;
178 return sum1 | (sum2 << 16);
179 }
180