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