zenilib  0.5.3.0
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1 /* adler32.c -- compute the Adler-32 checksum of a data stream
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
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
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 /* ========================================================================= */
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;
71
72  /* in case user likes doing a byte at a time, keep it fast */
73  if (len == 1) {
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--) {
92  }
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);
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--) {
121  }
123  MOD(sum2);
124  }
125
126  /* return recombined sums */
127  return adler | (sum2 << 16);
128 }
129
130 /* ========================================================================= */
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 /* ========================================================================= */
158  z_off_t len2;
159 {
161 }
162
166  z_off64_t len2;
167 {
169 }
unsigned long uLong
Definition: zconf.h:222
#define MOD(a)
Byte FAR Bytef
Definition: zconf.h:228
#define BASE
GLclampd n
Definition: glew.h:7287
#define ZEXPORT(x)
Definition: zconf.h:202
GLenum GLsizei len
Definition: glew.h:7035
#define NMAX
unsigned int uInt
Definition: zconf.h:221
#define Z_NULL
Definition: zlib.h:164
#define local
#define z_off64_t
Definition: zconf.h:400
#define z_off_t
Definition: zconf.h:254