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add4d470 | 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 "zutil.h" | |
9 | ||
10 | #define local static | |
11 | ||
12 | local uLong adler32_combine_ OF((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 | /* ========================================================================= */ | |
65 | uLong ZEXPORT adler32(adler, buf, len) | |
66 | uLong adler; | |
67 | const Bytef *buf; | |
68 | uInt len; | |
69 | { | |
70 | unsigned long sum2; | |
71 | unsigned n; | |
72 | ||
73 | /* split Adler-32 into component sums */ | |
74 | sum2 = (adler >> 16) & 0xffff; | |
75 | adler &= 0xffff; | |
76 | ||
77 | /* in case user likes doing a byte at a time, keep it fast */ | |
78 | if (len == 1) { | |
79 | adler += buf[0]; | |
80 | if (adler >= BASE) | |
81 | adler -= BASE; | |
82 | sum2 += adler; | |
83 | if (sum2 >= BASE) | |
84 | sum2 -= BASE; | |
85 | return adler | (sum2 << 16); | |
86 | } | |
87 | ||
88 | /* initial Adler-32 value (deferred check for len == 1 speed) */ | |
89 | if (buf == Z_NULL) | |
90 | return 1L; | |
91 | ||
92 | /* in case short lengths are provided, keep it somewhat fast */ | |
93 | if (len < 16) { | |
94 | while (len--) { | |
95 | adler += *buf++; | |
96 | sum2 += adler; | |
97 | } | |
98 | if (adler >= BASE) | |
99 | adler -= BASE; | |
100 | MOD28(sum2); /* only added so many BASE's */ | |
101 | return adler | (sum2 << 16); | |
102 | } | |
103 | ||
104 | /* do length NMAX blocks -- requires just one modulo operation */ | |
105 | while (len >= NMAX) { | |
106 | len -= NMAX; | |
107 | n = NMAX / 16; /* NMAX is divisible by 16 */ | |
108 | do { | |
109 | DO16(buf); /* 16 sums unrolled */ | |
110 | buf += 16; | |
111 | } while (--n); | |
112 | MOD(adler); | |
113 | MOD(sum2); | |
114 | } | |
115 | ||
116 | /* do remaining bytes (less than NMAX, still just one modulo) */ | |
117 | if (len) { /* avoid modulos if none remaining */ | |
118 | while (len >= 16) { | |
119 | len -= 16; | |
120 | DO16(buf); | |
121 | buf += 16; | |
122 | } | |
123 | while (len--) { | |
124 | adler += *buf++; | |
125 | sum2 += adler; | |
126 | } | |
127 | MOD(adler); | |
128 | MOD(sum2); | |
129 | } | |
130 | ||
131 | /* return recombined sums */ | |
132 | return adler | (sum2 << 16); | |
133 | } | |
134 | ||
135 | /* ========================================================================= */ | |
136 | local uLong adler32_combine_(adler1, adler2, len2) | |
137 | uLong adler1; | |
138 | uLong adler2; | |
139 | 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 ZEXPORT adler32_combine(adler1, adler2, len2) | |
166 | uLong adler1; | |
167 | uLong adler2; | |
168 | z_off_t len2; | |
169 | { | |
170 | return adler32_combine_(adler1, adler2, len2); | |
171 | } | |
172 | ||
173 | uLong ZEXPORT adler32_combine64(adler1, adler2, len2) | |
174 | uLong adler1; | |
175 | uLong adler2; | |
176 | z_off64_t len2; | |
177 | { | |
178 | return adler32_combine_(adler1, adler2, len2); | |
179 | } |