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