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