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 #include "hammer2_zlib_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 65521 /* 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 try it both ways to see which is faster */
26 #ifdef NO_DIVIDE
27 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
28 (thank you to John Reiser for pointing this out) */
29 # define CHOP(a) \
30 do { \
31 unsigned long tmp = a >> 16; \
32 a &= 0xffffUL; \
33 a += (tmp << 4) - tmp; \
34 } while (0)
35 # define MOD28(a) \
36 do { \
37 CHOP(a); \
38 if (a >= BASE) a -= BASE; \
39 } while (0)
40 # define MOD(a) \
41 do { \
42 CHOP(a); \
43 MOD28(a); \
44 } while (0)
45 # define MOD63(a) \
46 do { /* this assumes a is not negative */ \
47 z_off64_t tmp = a >> 32; \
48 a &= 0xffffffffL; \
49 a += (tmp << 8) - (tmp << 5) + tmp; \
50 tmp = a >> 16; \
51 a &= 0xffffL; \
52 a += (tmp << 4) - tmp; \
53 tmp = a >> 16; \
54 a &= 0xffffL; \
55 a += (tmp << 4) - tmp; \
56 if (a >= BASE) a -= BASE; \
57 } while (0)
58 #else
59 # define MOD(a) a %= BASE
60 # define MOD28(a) a %= BASE
61 # define MOD63(a) a %= BASE
62 #endif
63
64 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);
65 uLong adler32_combine(uLong adler1, uLong adler2, z_off_t len2);
66
67 /* ========================================================================= */
68 uLong
adler32(uLong adler,const Bytef * buf,uInt len)69 adler32(uLong adler, const Bytef *buf, 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 /* ========================================================================= */
137 local
138 uLong
adler32_combine_(uLong adler1,uLong adler2,z_off64_t len2)139 adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2)
140 {
141 unsigned long sum1;
142 unsigned long sum2;
143 unsigned rem;
144
145 /* for negative len, return invalid adler32 as a clue for debugging */
146 if (len2 < 0)
147 return 0xffffffffUL;
148
149 /* the derivation of this formula is left as an exercise for the reader */
150 MOD63(len2); /* assumes len2 >= 0 */
151 rem = (unsigned)len2;
152 sum1 = adler1 & 0xffff;
153 sum2 = rem * sum1;
154 MOD(sum2);
155 sum1 += (adler2 & 0xffff) + BASE - 1;
156 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
157 if (sum1 >= BASE) sum1 -= BASE;
158 if (sum1 >= BASE) sum1 -= BASE;
159 if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
160 if (sum2 >= BASE) sum2 -= BASE;
161 return sum1 | (sum2 << 16);
162 }
163
164 /* ========================================================================= */
165 uLong
adler32_combine(uLong adler1,uLong adler2,z_off_t len2)166 adler32_combine(uLong adler1, uLong adler2, z_off_t len2)
167 {
168 return adler32_combine_(adler1, adler2, len2);
169 }
170
171 uLong
adler32_combine64(uLong adler1,uLong adler2,z_off64_t len2)172 adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2)
173 {
174 return adler32_combine_(adler1, adler2, len2);
175 }
176