Line data Source code
1 : /* $OpenBSD: adler32.c,v 1.10 2011/07/07 02:57:24 deraadt Exp $ */
2 : /* adler32.c -- compute the Adler-32 checksum of a data stream
3 : * Copyright (C) 1995-2004 Mark Adler
4 : * For conditions of distribution and use, see copyright notice in zlib.h
5 : */
6 :
7 : #define ZLIB_INTERNAL
8 : #include "zlib.h"
9 :
10 : #define BASE 65521UL /* largest prime smaller than 65536 */
11 : #define NMAX 5552
12 : /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13 :
14 : #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
15 : #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
16 : #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
17 : #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
18 : #define DO16(buf) DO8(buf,0); DO8(buf,8);
19 :
20 : /* use NO_DIVIDE if your processor does not do division in hardware */
21 : #ifdef NO_DIVIDE
22 : # define MOD(a) \
23 : do { \
24 : if (a >= (BASE << 16)) a -= (BASE << 16); \
25 : if (a >= (BASE << 15)) a -= (BASE << 15); \
26 : if (a >= (BASE << 14)) a -= (BASE << 14); \
27 : if (a >= (BASE << 13)) a -= (BASE << 13); \
28 : if (a >= (BASE << 12)) a -= (BASE << 12); \
29 : if (a >= (BASE << 11)) a -= (BASE << 11); \
30 : if (a >= (BASE << 10)) a -= (BASE << 10); \
31 : if (a >= (BASE << 9)) a -= (BASE << 9); \
32 : if (a >= (BASE << 8)) a -= (BASE << 8); \
33 : if (a >= (BASE << 7)) a -= (BASE << 7); \
34 : if (a >= (BASE << 6)) a -= (BASE << 6); \
35 : if (a >= (BASE << 5)) a -= (BASE << 5); \
36 : if (a >= (BASE << 4)) a -= (BASE << 4); \
37 : if (a >= (BASE << 3)) a -= (BASE << 3); \
38 : if (a >= (BASE << 2)) a -= (BASE << 2); \
39 : if (a >= (BASE << 1)) a -= (BASE << 1); \
40 : if (a >= BASE) a -= BASE; \
41 : } while (0)
42 : # define MOD4(a) \
43 : do { \
44 : if (a >= (BASE << 4)) a -= (BASE << 4); \
45 : if (a >= (BASE << 3)) a -= (BASE << 3); \
46 : if (a >= (BASE << 2)) a -= (BASE << 2); \
47 : if (a >= (BASE << 1)) a -= (BASE << 1); \
48 : if (a >= BASE) a -= BASE; \
49 : } while (0)
50 : #else
51 : # define MOD(a) a %= BASE
52 : # define MOD4(a) a %= BASE
53 : #endif
54 :
55 : /* ========================================================================= */
56 0 : uLong ZEXPORT adler32(adler, buf, len)
57 : uLong adler;
58 : const Bytef *buf;
59 : uInt len;
60 : {
61 : unsigned long sum2;
62 : unsigned n;
63 :
64 : /* split Adler-32 into component sums */
65 0 : sum2 = (adler >> 16) & 0xffff;
66 0 : adler &= 0xffff;
67 :
68 : /* in case user likes doing a byte at a time, keep it fast */
69 0 : if (len == 1) {
70 0 : adler += buf[0];
71 0 : if (adler >= BASE)
72 0 : adler -= BASE;
73 0 : sum2 += adler;
74 0 : if (sum2 >= BASE)
75 0 : sum2 -= BASE;
76 0 : return adler | (sum2 << 16);
77 : }
78 :
79 : /* initial Adler-32 value (deferred check for len == 1 speed) */
80 0 : if (buf == Z_NULL)
81 0 : return 1L;
82 :
83 : /* in case short lengths are provided, keep it somewhat fast */
84 0 : if (len < 16) {
85 0 : while (len--) {
86 0 : adler += *buf++;
87 0 : sum2 += adler;
88 : }
89 0 : if (adler >= BASE)
90 0 : adler -= BASE;
91 0 : MOD4(sum2); /* only added so many BASE's */
92 0 : return adler | (sum2 << 16);
93 : }
94 :
95 : /* do length NMAX blocks -- requires just one modulo operation */
96 0 : while (len >= NMAX) {
97 0 : len -= NMAX;
98 : n = NMAX / 16; /* NMAX is divisible by 16 */
99 0 : do {
100 0 : DO16(buf); /* 16 sums unrolled */
101 0 : buf += 16;
102 0 : } while (--n);
103 0 : MOD(adler);
104 0 : MOD(sum2);
105 : }
106 :
107 : /* do remaining bytes (less than NMAX, still just one modulo) */
108 0 : if (len) { /* avoid modulos if none remaining */
109 0 : while (len >= 16) {
110 0 : len -= 16;
111 0 : DO16(buf);
112 0 : buf += 16;
113 : }
114 0 : while (len--) {
115 0 : adler += *buf++;
116 0 : sum2 += adler;
117 : }
118 0 : MOD(adler);
119 0 : MOD(sum2);
120 0 : }
121 :
122 : /* return recombined sums */
123 0 : return adler | (sum2 << 16);
124 0 : }
125 :
126 : /* ========================================================================= */
127 0 : uLong ZEXPORT adler32_combine(adler1, adler2, len2)
128 : uLong adler1;
129 : uLong adler2;
130 : z_off_t len2;
131 : {
132 : unsigned long sum1;
133 : unsigned long sum2;
134 : unsigned rem;
135 :
136 : /* the derivation of this formula is left as an exercise for the reader */
137 0 : rem = (unsigned)(len2 % BASE);
138 0 : sum1 = adler1 & 0xffff;
139 0 : sum2 = rem * sum1;
140 0 : MOD(sum2);
141 0 : sum1 += (adler2 & 0xffff) + BASE - 1;
142 0 : sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
143 0 : if (sum1 > BASE) sum1 -= BASE;
144 0 : if (sum1 > BASE) sum1 -= BASE;
145 0 : if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
146 0 : if (sum2 > BASE) sum2 -= BASE;
147 0 : return sum1 | (sum2 << 16);
148 : }
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