Annotation of embedaddon/sudo/zlib/adler32.c, revision 1.1.1.1
1.1 misho 1: /* adler32.c -- compute the Adler-32 checksum of a data stream
2: * Copyright (C) 1995-2007 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_(uLong adler1, uLong adler2, z_off64_t len2);
13:
14: #define BASE 65521UL /* 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: #ifdef NO_DIVIDE
26: # define MOD(a) \
27: do { \
28: if (a >= (BASE << 16)) a -= (BASE << 16); \
29: if (a >= (BASE << 15)) a -= (BASE << 15); \
30: if (a >= (BASE << 14)) a -= (BASE << 14); \
31: if (a >= (BASE << 13)) a -= (BASE << 13); \
32: if (a >= (BASE << 12)) a -= (BASE << 12); \
33: if (a >= (BASE << 11)) a -= (BASE << 11); \
34: if (a >= (BASE << 10)) a -= (BASE << 10); \
35: if (a >= (BASE << 9)) a -= (BASE << 9); \
36: if (a >= (BASE << 8)) a -= (BASE << 8); \
37: if (a >= (BASE << 7)) a -= (BASE << 7); \
38: if (a >= (BASE << 6)) a -= (BASE << 6); \
39: if (a >= (BASE << 5)) a -= (BASE << 5); \
40: if (a >= (BASE << 4)) a -= (BASE << 4); \
41: if (a >= (BASE << 3)) a -= (BASE << 3); \
42: if (a >= (BASE << 2)) a -= (BASE << 2); \
43: if (a >= (BASE << 1)) a -= (BASE << 1); \
44: if (a >= BASE) a -= BASE; \
45: } while (0)
46: # define MOD4(a) \
47: do { \
48: if (a >= (BASE << 4)) a -= (BASE << 4); \
49: if (a >= (BASE << 3)) a -= (BASE << 3); \
50: if (a >= (BASE << 2)) a -= (BASE << 2); \
51: if (a >= (BASE << 1)) a -= (BASE << 1); \
52: if (a >= BASE) a -= BASE; \
53: } while (0)
54: #else
55: # define MOD(a) a %= BASE
56: # define MOD4(a) a %= BASE
57: #endif
58:
59: /* ========================================================================= */
60: uLong ZEXPORT adler32(adler, buf, len)
61: uLong adler;
62: const Bytef *buf;
63: uInt len;
64: {
65: unsigned long sum2;
66: unsigned n;
67:
68: /* split Adler-32 into component sums */
69: sum2 = (adler >> 16) & 0xffff;
70: adler &= 0xffff;
71:
72: /* in case user likes doing a byte at a time, keep it fast */
73: if (len == 1) {
74: adler += buf[0];
75: if (adler >= BASE)
76: adler -= BASE;
77: sum2 += adler;
78: if (sum2 >= BASE)
79: sum2 -= BASE;
80: return adler | (sum2 << 16);
81: }
82:
83: /* initial Adler-32 value (deferred check for len == 1 speed) */
84: if (buf == Z_NULL)
85: return 1L;
86:
87: /* in case short lengths are provided, keep it somewhat fast */
88: if (len < 16) {
89: while (len--) {
90: adler += *buf++;
91: sum2 += adler;
92: }
93: if (adler >= BASE)
94: adler -= BASE;
95: MOD4(sum2); /* only added so many BASE's */
96: return adler | (sum2 << 16);
97: }
98:
99: /* do length NMAX blocks -- requires just one modulo operation */
100: while (len >= NMAX) {
101: len -= NMAX;
102: n = NMAX / 16; /* NMAX is divisible by 16 */
103: do {
104: DO16(buf); /* 16 sums unrolled */
105: buf += 16;
106: } while (--n);
107: MOD(adler);
108: MOD(sum2);
109: }
110:
111: /* do remaining bytes (less than NMAX, still just one modulo) */
112: if (len) { /* avoid modulos if none remaining */
113: while (len >= 16) {
114: len -= 16;
115: DO16(buf);
116: buf += 16;
117: }
118: while (len--) {
119: adler += *buf++;
120: sum2 += adler;
121: }
122: MOD(adler);
123: MOD(sum2);
124: }
125:
126: /* return recombined sums */
127: return adler | (sum2 << 16);
128: }
129:
130: /* ========================================================================= */
131: local uLong adler32_combine_(adler1, adler2, len2)
132: uLong adler1;
133: uLong adler2;
134: z_off64_t len2;
135: {
136: unsigned long sum1;
137: unsigned long sum2;
138: unsigned rem;
139:
140: /* the derivation of this formula is left as an exercise for the reader */
141: rem = (unsigned)(len2 % BASE);
142: sum1 = adler1 & 0xffff;
143: sum2 = rem * sum1;
144: MOD(sum2);
145: sum1 += (adler2 & 0xffff) + BASE - 1;
146: sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
147: if (sum1 >= BASE) sum1 -= BASE;
148: if (sum1 >= BASE) sum1 -= BASE;
149: if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);
150: if (sum2 >= BASE) sum2 -= BASE;
151: return sum1 | (sum2 << 16);
152: }
153:
154: /* ========================================================================= */
155: uLong ZEXPORT adler32_combine(adler1, adler2, len2)
156: uLong adler1;
157: uLong adler2;
158: z_off_t len2;
159: {
160: return adler32_combine_(adler1, adler2, len2);
161: }
162:
163: uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
164: uLong adler1;
165: uLong adler2;
166: z_off64_t len2;
167: {
168: return adler32_combine_(adler1, adler2, len2);
169: }
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