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 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
9
10 #define BASE 65521U /* largest prime smaller than 65536 */
11 #define NMAX 5552
12 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13
14 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
15 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
16 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
17 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
18 #define DO16(buf) DO8(buf,0); DO8(buf,8);
19
20 /* use NO_DIVIDE if your processor does not do division in hardware --
21 try it both ways to see which is faster */
22 #ifdef NO_DIVIDE
23 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
24 (thank you to John Reiser for pointing this out) */
25 # define CHOP(a) \
26 do { \
27 unsigned long tmp = a >> 16; \
28 a &= 0xffffUL; \
29 a += (tmp << 4) - tmp; \
30 } while (0)
31 # define MOD28(a) \
32 do { \
33 CHOP(a); \
34 if (a >= BASE) a -= BASE; \
35 } while (0)
36 # define MOD(a) \
37 do { \
38 CHOP(a); \
39 MOD28(a); \
40 } while (0)
41 # define MOD63(a) \
42 do { /* this assumes a is not negative */ \
43 z_off64_t tmp = a >> 32; \
44 a &= 0xffffffffL; \
45 a += (tmp << 8) - (tmp << 5) + tmp; \
46 tmp = a >> 16; \
47 a &= 0xffffL; \
48 a += (tmp << 4) - tmp; \
49 tmp = a >> 16; \
50 a &= 0xffffL; \
51 a += (tmp << 4) - tmp; \
52 if (a >= BASE) a -= BASE; \
53 } while (0)
54 #else
55 # define MOD(a) a %= BASE
56 # define MOD28(a) a %= BASE
57 # define MOD63(a) a %= BASE
58 #endif
59
60 /* ========================================================================= */
adler32_z(uLong adler,const Bytef * buf,z_size_t len)61 uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len)
62 {
63 unsigned long sum2;
64 unsigned n;
65
66 /* split Adler-32 into component sums */
67 sum2 = (adler >> 16) & 0xffff;
68 adler &= 0xffff;
69
70 /* in case user likes doing a byte at a time, keep it fast */
71 if (len == 1) {
72 adler += buf[0];
73 if (adler >= BASE)
74 adler -= BASE;
75 sum2 += adler;
76 if (sum2 >= BASE)
77 sum2 -= BASE;
78 return adler | (sum2 << 16);
79 }
80
81 /* initial Adler-32 value (deferred check for len == 1 speed) */
82 if (buf == Z_NULL)
83 return 1L;
84
85 /* in case short lengths are provided, keep it somewhat fast */
86 if (len < 16) {
87 while (len--) {
88 adler += *buf++;
89 sum2 += adler;
90 }
91 if (adler >= BASE)
92 adler -= BASE;
93 MOD28(sum2); /* only added so many BASE's */
94 return adler | (sum2 << 16);
95 }
96
97 /* do length NMAX blocks -- requires just one modulo operation */
98 while (len >= NMAX) {
99 len -= NMAX;
100 n = NMAX / 16; /* NMAX is divisible by 16 */
101 do {
102 DO16(buf); /* 16 sums unrolled */
103 buf += 16;
104 } while (--n);
105 MOD(adler);
106 MOD(sum2);
107 }
108
109 /* do remaining bytes (less than NMAX, still just one modulo) */
110 if (len) { /* avoid modulos if none remaining */
111 while (len >= 16) {
112 len -= 16;
113 DO16(buf);
114 buf += 16;
115 }
116 while (len--) {
117 adler += *buf++;
118 sum2 += adler;
119 }
120 MOD(adler);
121 MOD(sum2);
122 }
123
124 /* return recombined sums */
125 return adler | (sum2 << 16);
126 }
127
128 /* ========================================================================= */
adler32(uLong adler,const Bytef * buf,uInt len)129 uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)
130 {
131 return adler32_z(adler, buf, len);
132 }
133
134 /* ========================================================================= */
adler32_combine_(uLong adler1,uLong adler2,z_off64_t len2)135 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2)
136 {
137 unsigned long sum1;
138 unsigned long sum2;
139 unsigned rem;
140
141 /* for negative len, return invalid adler32 as a clue for debugging */
142 if (len2 < 0)
143 return 0xffffffffUL;
144
145 /* the derivation of this formula is left as an exercise for the reader */
146 MOD63(len2); /* assumes len2 >= 0 */
147 rem = (unsigned)len2;
148 sum1 = adler1 & 0xffff;
149 sum2 = rem * sum1;
150 MOD(sum2);
151 sum1 += (adler2 & 0xffff) + BASE - 1;
152 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
153 if (sum1 >= BASE) sum1 -= BASE;
154 if (sum1 >= BASE) sum1 -= BASE;
155 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
156 if (sum2 >= BASE) sum2 -= BASE;
157 return sum1 | (sum2 << 16);
158 }
159
160 /* ========================================================================= */
adler32_combine(uLong adler1,uLong adler2,z_off_t len2)161 uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2)
162 {
163 return adler32_combine_(adler1, adler2, len2);
164 }
165
adler32_combine64(uLong adler1,uLong adler2,z_off64_t len2)166 uLong ZEXPORT adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2)
167 {
168 return adler32_combine_(adler1, adler2, len2);
169 }
170