1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2011, 2016 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6 #include "zutil.h"
7
8 #define BASE 65521U /* largest prime smaller than 65536 */
9 #define NMAX 5552
10 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
11
12 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
13 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
14 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
15 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
16 #define DO16(buf) DO8(buf,0); DO8(buf,8);
17
18 /* use NO_DIVIDE if your processor does not do division in hardware --
19 try it both ways to see which is faster */
20 #ifdef NO_DIVIDE
21 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
22 (thank you to John Reiser for pointing this out) */
23 # define CHOP(a) \
24 do { \
25 unsigned long tmp = a >> 16; \
26 a &= 0xffffUL; \
27 a += (tmp << 4) - tmp; \
28 } while (0)
29 # define MOD28(a) \
30 do { \
31 CHOP(a); \
32 if (a >= BASE) a -= BASE; \
33 } while (0)
34 # define MOD(a) \
35 do { \
36 CHOP(a); \
37 MOD28(a); \
38 } while (0)
39 # define MOD63(a) \
40 do { /* this assumes a is not negative */ \
41 z_off64_t tmp = a >> 32; \
42 a &= 0xffffffffL; \
43 a += (tmp << 8) - (tmp << 5) + tmp; \
44 tmp = a >> 16; \
45 a &= 0xffffL; \
46 a += (tmp << 4) - tmp; \
47 tmp = a >> 16; \
48 a &= 0xffffL; \
49 a += (tmp << 4) - tmp; \
50 if (a >= BASE) a -= BASE; \
51 } while (0)
52 #else
53 # define MOD(a) a %= BASE
54 # define MOD28(a) a %= BASE
55 # define MOD63(a) a %= BASE
56 #endif
57
58 /* ========================================================================= */
adler32_z(uLong adler,const Bytef * buf,z_size_t len)59 uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len) {
60 unsigned long sum2;
61 unsigned n;
62
63 /* split Adler-32 into component sums */
64 sum2 = (adler >> 16) & 0xffff;
65 adler &= 0xffff;
66
67 /* in case user likes doing a byte at a time, keep it fast */
68 if (len == 1) {
69 adler += buf[0];
70 if (adler >= BASE)
71 adler -= BASE;
72 sum2 += adler;
73 if (sum2 >= BASE)
74 sum2 -= BASE;
75 return adler | (sum2 << 16);
76 }
77
78 /* initial Adler-32 value (deferred check for len == 1 speed) */
79 if (buf == Z_NULL)
80 return 1L;
81
82 /* in case short lengths are provided, keep it somewhat fast */
83 if (len < 16) {
84 while (len--) {
85 adler += *buf++;
86 sum2 += adler;
87 }
88 if (adler >= BASE)
89 adler -= BASE;
90 MOD28(sum2); /* only added so many BASE's */
91 return adler | (sum2 << 16);
92 }
93
94 /* do length NMAX blocks -- requires just one modulo operation */
95 while (len >= NMAX) {
96 len -= NMAX;
97 n = NMAX / 16; /* NMAX is divisible by 16 */
98 do {
99 DO16(buf); /* 16 sums unrolled */
100 buf += 16;
101 } while (--n);
102 MOD(adler);
103 MOD(sum2);
104 }
105
106 /* do remaining bytes (less than NMAX, still just one modulo) */
107 if (len) { /* avoid modulos if none remaining */
108 while (len >= 16) {
109 len -= 16;
110 DO16(buf);
111 buf += 16;
112 }
113 while (len--) {
114 adler += *buf++;
115 sum2 += adler;
116 }
117 MOD(adler);
118 MOD(sum2);
119 }
120
121 /* return recombined sums */
122 return adler | (sum2 << 16);
123 }
124
125 /* ========================================================================= */
adler32(uLong adler,const Bytef * buf,uInt len)126 uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len) {
127 return adler32_z(adler, buf, len);
128 }
129
130 /* ========================================================================= */
adler32_combine_(uLong adler1,uLong adler2,z_off64_t len2)131 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2) {
132 unsigned long sum1;
133 unsigned long sum2;
134 unsigned rem;
135
136 /* for negative len, return invalid adler32 as a clue for debugging */
137 if (len2 < 0)
138 return 0xffffffffUL;
139
140 /* the derivation of this formula is left as an exercise for the reader */
141 MOD63(len2); /* assumes len2 >= 0 */
142 rem = (unsigned)len2;
143 sum1 = adler1 & 0xffff;
144 sum2 = rem * sum1;
145 MOD(sum2);
146 sum1 += (adler2 & 0xffff) + BASE - 1;
147 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
148 if (sum1 >= BASE) sum1 -= BASE;
149 if (sum1 >= BASE) sum1 -= BASE;
150 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
151 if (sum2 >= BASE) sum2 -= BASE;
152 return sum1 | (sum2 << 16);
153 }
154
155 /* ========================================================================= */
adler32_combine(uLong adler1,uLong adler2,z_off_t len2)156 uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2) {
157 return adler32_combine_(adler1, adler2, len2);
158 }
159
adler32_combine64(uLong adler1,uLong adler2,z_off64_t len2)160 uLong ZEXPORT adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2) {
161 return adler32_combine_(adler1, adler2, len2);
162 }
163