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Source at commit 1085 created 13 years 1 month ago. By azimutz, Runaway "min"; fixes build. | |
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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 | ␊ |
12 | local 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 | /* ========================================================================= */␊ |
60 | uLong 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 | /* ========================================================================= */␊ |
131 | local 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 | /* ========================================================================= */␊ |
155 | uLong 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 | ␊ |
163 | uLong 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 | }␊ |
170 |