Line data Source code
1 : /* adler32.c -- compute the Adler-32 checksum of a data stream
2 : * Copyright (C) 1995-2011, 2016 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 : local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
11 :
12 : #define BASE 65521U /* largest prime smaller than 65536 */
13 : #define NMAX 5552
14 : /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
15 :
16 : #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
17 : #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
18 : #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
19 : #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
20 : #define DO16(buf) DO8(buf,0); DO8(buf,8);
21 :
22 : /* use NO_DIVIDE if your processor does not do division in hardware --
23 : try it both ways to see which is faster */
24 : #ifdef NO_DIVIDE
25 : /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
26 : (thank you to John Reiser for pointing this out) */
27 : # define CHOP(a) \
28 : do { \
29 : unsigned long tmp = a >> 16; \
30 : a &= 0xffffUL; \
31 : a += (tmp << 4) - tmp; \
32 : } while (0)
33 : # define MOD28(a) \
34 : do { \
35 : CHOP(a); \
36 : if (a >= BASE) a -= BASE; \
37 : } while (0)
38 : # define MOD(a) \
39 : do { \
40 : CHOP(a); \
41 : MOD28(a); \
42 : } while (0)
43 : # define MOD63(a) \
44 : do { /* this assumes a is not negative */ \
45 : z_off64_t tmp = a >> 32; \
46 : a &= 0xffffffffL; \
47 : a += (tmp << 8) - (tmp << 5) + tmp; \
48 : tmp = a >> 16; \
49 : a &= 0xffffL; \
50 : a += (tmp << 4) - tmp; \
51 : tmp = a >> 16; \
52 : a &= 0xffffL; \
53 : a += (tmp << 4) - tmp; \
54 : if (a >= BASE) a -= BASE; \
55 : } while (0)
56 : #else
57 : # define MOD(a) a %= BASE
58 : # define MOD28(a) a %= BASE
59 : # define MOD63(a) a %= BASE
60 : #endif
61 :
62 : /* ========================================================================= */
63 1808 : uLong ZEXPORT adler32_z(adler, buf, len)
64 : uLong adler;
65 : const Bytef *buf;
66 : z_size_t len;
67 : {
68 : unsigned long sum2;
69 : unsigned n;
70 :
71 : /* split Adler-32 into component sums */
72 1808 : sum2 = (adler >> 16) & 0xffff;
73 1808 : adler &= 0xffff;
74 :
75 : /* in case user likes doing a byte at a time, keep it fast */
76 1808 : if (len == 1) {
77 0 : adler += buf[0];
78 0 : if (adler >= BASE)
79 0 : adler -= BASE;
80 0 : sum2 += adler;
81 0 : if (sum2 >= BASE)
82 0 : sum2 -= BASE;
83 0 : return adler | (sum2 << 16);
84 : }
85 :
86 : /* initial Adler-32 value (deferred check for len == 1 speed) */
87 1808 : if (buf == Z_NULL)
88 266 : return 1L;
89 :
90 : /* in case short lengths are provided, keep it somewhat fast */
91 1542 : if (len < 16) {
92 0 : while (len--) {
93 0 : adler += *buf++;
94 0 : sum2 += adler;
95 : }
96 0 : if (adler >= BASE)
97 0 : adler -= BASE;
98 0 : MOD28(sum2); /* only added so many BASE's */
99 0 : return adler | (sum2 << 16);
100 : }
101 :
102 : /* do length NMAX blocks -- requires just one modulo operation */
103 3252 : while (len >= NMAX) {
104 168 : len -= NMAX;
105 168 : n = NMAX / 16; /* NMAX is divisible by 16 */
106 : do {
107 58296 : DO16(buf); /* 16 sums unrolled */
108 58296 : buf += 16;
109 58296 : } while (--n);
110 168 : MOD(adler);
111 168 : MOD(sum2);
112 : }
113 :
114 : /* do remaining bytes (less than NMAX, still just one modulo) */
115 1542 : if (len) { /* avoid modulos if none remaining */
116 17822 : while (len >= 16) {
117 14738 : len -= 16;
118 14738 : DO16(buf);
119 14738 : buf += 16;
120 : }
121 5073 : while (len--) {
122 1989 : adler += *buf++;
123 1989 : sum2 += adler;
124 : }
125 1542 : MOD(adler);
126 1542 : MOD(sum2);
127 : }
128 :
129 : /* return recombined sums */
130 1542 : return adler | (sum2 << 16);
131 : }
132 :
133 : /* ========================================================================= */
134 1808 : uLong ZEXPORT adler32(adler, buf, len)
135 : uLong adler;
136 : const Bytef *buf;
137 : uInt len;
138 : {
139 1808 : return adler32_z(adler, buf, len);
140 : }
141 :
142 : /* ========================================================================= */
143 0 : local uLong adler32_combine_(adler1, adler2, len2)
144 : uLong adler1;
145 : uLong adler2;
146 : z_off64_t len2;
147 : {
148 : unsigned long sum1;
149 : unsigned long sum2;
150 : unsigned rem;
151 :
152 : /* for negative len, return invalid adler32 as a clue for debugging */
153 0 : if (len2 < 0)
154 0 : return 0xffffffffUL;
155 :
156 : /* the derivation of this formula is left as an exercise for the reader */
157 0 : MOD63(len2); /* assumes len2 >= 0 */
158 0 : rem = (unsigned)len2;
159 0 : sum1 = adler1 & 0xffff;
160 0 : sum2 = rem * sum1;
161 0 : MOD(sum2);
162 0 : sum1 += (adler2 & 0xffff) + BASE - 1;
163 0 : sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
164 0 : if (sum1 >= BASE) sum1 -= BASE;
165 0 : if (sum1 >= BASE) sum1 -= BASE;
166 0 : if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
167 0 : if (sum2 >= BASE) sum2 -= BASE;
168 0 : return sum1 | (sum2 << 16);
169 : }
170 :
171 : /* ========================================================================= */
172 0 : uLong ZEXPORT adler32_combine(adler1, adler2, len2)
173 : uLong adler1;
174 : uLong adler2;
175 : z_off_t len2;
176 : {
177 0 : return adler32_combine_(adler1, adler2, len2);
178 : }
179 :
180 0 : uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
181 : uLong adler1;
182 : uLong adler2;
183 : z_off64_t len2;
184 : {
185 0 : return adler32_combine_(adler1, adler2, len2);
186 : }
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