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 5769 : 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 5769 : sum2 = (adler >> 16) & 0xffff;
70 5769 : adler &= 0xffff;
71 :
72 : /* in case user likes doing a byte at a time, keep it fast */
73 5769 : if (len == 1) {
74 0 : adler += buf[0];
75 0 : if (adler >= BASE)
76 0 : adler -= BASE;
77 0 : sum2 += adler;
78 0 : if (sum2 >= BASE)
79 0 : sum2 -= BASE;
80 0 : return adler | (sum2 << 16);
81 : }
82 :
83 : /* initial Adler-32 value (deferred check for len == 1 speed) */
84 5769 : if (buf == Z_NULL)
85 5256 : return 1L;
86 :
87 : /* in case short lengths are provided, keep it somewhat fast */
88 513 : if (len < 16) {
89 1082 : while (len--) {
90 922 : adler += *buf++;
91 922 : sum2 += adler;
92 : }
93 80 : if (adler >= BASE)
94 0 : adler -= BASE;
95 80 : MOD4(sum2); /* only added so many BASE's */
96 80 : return adler | (sum2 << 16);
97 : }
98 :
99 : /* do length NMAX blocks -- requires just one modulo operation */
100 867 : while (len >= NMAX) {
101 1 : len -= NMAX;
102 1 : n = NMAX / 16; /* NMAX is divisible by 16 */
103 : do {
104 347 : DO16(buf); /* 16 sums unrolled */
105 347 : buf += 16;
106 347 : } while (--n);
107 1 : MOD(adler);
108 1 : MOD(sum2);
109 : }
110 :
111 : /* do remaining bytes (less than NMAX, still just one modulo) */
112 433 : if (len) { /* avoid modulos if none remaining */
113 5113 : while (len >= 16) {
114 4247 : len -= 16;
115 4247 : DO16(buf);
116 4247 : buf += 16;
117 : }
118 1550 : while (len--) {
119 684 : adler += *buf++;
120 684 : sum2 += adler;
121 : }
122 433 : MOD(adler);
123 433 : MOD(sum2);
124 : }
125 :
126 : /* return recombined sums */
127 433 : return adler | (sum2 << 16);
128 : }
129 :
130 : /* ========================================================================= */
131 0 : 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 0 : rem = (unsigned)(len2 % BASE);
142 0 : sum1 = adler1 & 0xffff;
143 0 : sum2 = rem * sum1;
144 0 : MOD(sum2);
145 0 : sum1 += (adler2 & 0xffff) + BASE - 1;
146 0 : sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
147 0 : if (sum1 >= BASE) sum1 -= BASE;
148 0 : if (sum1 >= BASE) sum1 -= BASE;
149 0 : if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
150 0 : if (sum2 >= BASE) sum2 -= BASE;
151 0 : return sum1 | (sum2 << 16);
152 : }
153 :
154 : /* ========================================================================= */
155 0 : uLong ZEXPORT adler32_combine(adler1, adler2, len2)
156 : uLong adler1;
157 : uLong adler2;
158 : z_off_t len2;
159 : {
160 0 : return adler32_combine_(adler1, adler2, len2);
161 : }
162 :
163 0 : uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
164 : uLong adler1;
165 : uLong adler2;
166 : z_off64_t len2;
167 : {
168 0 : return adler32_combine_(adler1, adler2, len2);
169 : }
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