pngcrush  1.8.13 About: Pngcrush is an optimizer for PNG (Portable Network Graphics) files.   Fossies Dox: pngcrush-1.8.13.tar.gz  ("inofficial" and yet experimental doxygen-generated source code documentation)
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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
11
12 #define BASE 65521U /* largest prime smaller than 65536 */
13 #define NMAX 5552
14 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
15
17 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
18 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
19 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
20 #define DO16(buf) DO8(buf,0); DO8(buf,8);
21
22 /* use NO_DIVIDE if your processor does not do division in hardware --
23  try it both ways to see which is faster */
24 #ifdef NO_DIVIDE
25 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
26  (thank you to John Reiser for pointing this out) */
27 # define CHOP(a) \
28  do { \
29  unsigned long tmp = a >> 16; \
30  a &= 0xffffUL; \
31  a += (tmp << 4) - tmp; \
32  } while (0)
33 # define MOD28(a) \
34  do { \
35  CHOP(a); \
36  if (a >= BASE) a -= BASE; \
37  } while (0)
38 # define MOD(a) \
39  do { \
40  CHOP(a); \
41  MOD28(a); \
42  } while (0)
43 # define MOD63(a) \
44  do { /* this assumes a is not negative */ \
45  z_off64_t tmp = a >> 32; \
46  a &= 0xffffffffL; \
47  a += (tmp << 8) - (tmp << 5) + tmp; \
48  tmp = a >> 16; \
49  a &= 0xffffL; \
50  a += (tmp << 4) - tmp; \
51  tmp = a >> 16; \
52  a &= 0xffffL; \
53  a += (tmp << 4) - tmp; \
54  if (a >= BASE) a -= BASE; \
55  } while (0)
56 #else
57 # define MOD(a) a %= BASE
58 # define MOD28(a) a %= BASE
59 # define MOD63(a) a %= BASE
60 #endif
61
62 /* ========================================================================= */
65  const Bytef *buf;
66  z_size_t len;
67 {
68  unsigned long sum2;
69  unsigned n;
70
71  /* split Adler-32 into component sums */
72  sum2 = (adler >> 16) & 0xffff;
74
75  /* in case user likes doing a byte at a time, keep it fast */
76  if (len == 1) {
81  if (sum2 >= BASE)
82  sum2 -= BASE;
83  return adler | (sum2 << 16);
84  }
85
86  /* initial Adler-32 value (deferred check for len == 1 speed) */
87  if (buf == Z_NULL)
88  return 1L;
89
90  /* in case short lengths are provided, keep it somewhat fast */
91  if (len < 16) {
92  while (len--) {
95  }
98  MOD28(sum2); /* only added so many BASE's */
99  return adler | (sum2 << 16);
100  }
101
102  /* do length NMAX blocks -- requires just one modulo operation */
103  while (len >= NMAX) {
104  len -= NMAX;
105  n = NMAX / 16; /* NMAX is divisible by 16 */
106  do {
107  DO16(buf); /* 16 sums unrolled */
108  buf += 16;
109  } while (--n);
111  MOD(sum2);
112  }
113
114  /* do remaining bytes (less than NMAX, still just one modulo) */
115  if (len) { /* avoid modulos if none remaining */
116  while (len >= 16) {
117  len -= 16;
118  DO16(buf);
119  buf += 16;
120  }
121  while (len--) {
124  }
126  MOD(sum2);
127  }
128
129  /* return recombined sums */
130  return adler | (sum2 << 16);
131 }
132
133 /* ========================================================================= */
136  const Bytef *buf;
137  uInt len;
138 {
140 }
141
142 /* ========================================================================= */
146  z_off64_t len2;
147 {
148  unsigned long sum1;
149  unsigned long sum2;
150  unsigned rem;
151
152  /* for negative len, return invalid adler32 as a clue for debugging */
153  if (len2 < 0)
154  return 0xffffffffUL;
155
156  /* the derivation of this formula is left as an exercise for the reader */
157  MOD63(len2); /* assumes len2 >= 0 */
158  rem = (unsigned)len2;
159  sum1 = adler1 & 0xffff;
160  sum2 = rem * sum1;
161  MOD(sum2);
162  sum1 += (adler2 & 0xffff) + BASE - 1;
163  sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
164  if (sum1 >= BASE) sum1 -= BASE;
165  if (sum1 >= BASE) sum1 -= BASE;
166  if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
167  if (sum2 >= BASE) sum2 -= BASE;
168  return sum1 | (sum2 << 16);
169 }
170
171 /* ========================================================================= */
175  z_off_t len2;
176 {
178 }
179
183  z_off64_t len2;
184 {
186 }
Definition: png.c:2253
z_size_t
unsigned long z_size_t
Definition: zconf.h:250
DO16
#define DO16(buf)
uLong
unsigned long uLong
Definition: zconf.h:394
MOD
#define MOD(a)
BASE
#define BASE
z_off_t
#define z_off_t
Definition: zconf.h:504
OF
#define OF(args)
Definition: zconf.h:292
NMAX
#define NMAX
Z_NULL
#define Z_NULL
Definition: zlib.h:212
z_off64_t
#define z_off64_t
Definition: zconf.h:513
MOD28
#define MOD28(a)
local
#define local
Definition: gzguts.h:118
zutil.h
ZEXPORT
#define ZEXPORT
Definition: zconf.h:380
uInt
unsigned int uInt
Definition: zconf.h:393
Bytef
Byte Bytef
Definition: zconf.h:400
MOD63
#define MOD63(a)