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 /* ========================================================================= */
adler32(adler,buf,len)60 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 sum2 = (adler >> 16) & 0xffff;
70 adler &= 0xffff;
71
72 /* in case user likes doing a byte at a time, keep it fast */
73 if (len == 1) {
74 adler += buf[0];
75 if (adler >= BASE)
76 adler -= BASE;
77 sum2 += adler;
78 if (sum2 >= BASE)
79 sum2 -= BASE;
80 return adler | (sum2 << 16);
81 }
82
83 /* initial Adler-32 value (deferred check for len == 1 speed) */
84 if (buf == Z_NULL)
85 return 1L;
86
87 /* in case short lengths are provided, keep it somewhat fast */
88 if (len < 16) {
89 while (len--) {
90 adler += *buf++;
91 sum2 += adler;
92 }
93 if (adler >= BASE)
94 adler -= BASE;
95 MOD4(sum2); /* only added so many BASE's */
96 return adler | (sum2 << 16);
97 }
98
99 /* do length NMAX blocks -- requires just one modulo operation */
100 while (len >= NMAX) {
101 len -= NMAX;
102 n = NMAX / 16; /* NMAX is divisible by 16 */
103 do {
104 DO16(buf); /* 16 sums unrolled */
105 buf += 16;
106 } while (--n);
107 MOD(adler);
108 MOD(sum2);
109 }
110
111 /* do remaining bytes (less than NMAX, still just one modulo) */
112 if (len) { /* avoid modulos if none remaining */
113 while (len >= 16) {
114 len -= 16;
115 DO16(buf);
116 buf += 16;
117 }
118 while (len--) {
119 adler += *buf++;
120 sum2 += adler;
121 }
122 MOD(adler);
123 MOD(sum2);
124 }
125
126 /* return recombined sums */
127 return adler | (sum2 << 16);
128 }
129
130 /* ========================================================================= */
adler32_combine_(adler1,adler2,len2)131 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 rem = (unsigned)(len2 % BASE);
142 sum1 = adler1 & 0xffff;
143 sum2 = rem * sum1;
144 MOD(sum2);
145 sum1 += (adler2 & 0xffff) + BASE - 1;
146 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
147 if (sum1 >= BASE) sum1 -= BASE;
148 if (sum1 >= BASE) sum1 -= BASE;
149 if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
150 if (sum2 >= BASE) sum2 -= BASE;
151 return sum1 | (sum2 << 16);
152 }
153
154 /* ========================================================================= */
adler32_combine(adler1,adler2,len2)155 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
156 uLong adler1;
157 uLong adler2;
158 z_off_t len2;
159 {
160 return adler32_combine_(adler1, adler2, len2);
161 }
162
adler32_combine64(adler1,adler2,len2)163 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
164 uLong adler1;
165 uLong adler2;
166 z_off64_t len2;
167 {
168 return adler32_combine_(adler1, adler2, len2);
169 }
170