adler32.c
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1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2  * Copyright (C) 1995-2004 Mark Adler
3  * For conditions of distribution and use, see copyright notice in zlib.h
4  */
5 
6 /* @(#) $Id$ */
7 
8 #define ZLIB_INTERNAL
9 #include "zlib.h"
10 
11 #define BASE 65521UL /* largest prime smaller than 65536 */
12 #define NMAX 5552
13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
14 
15 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
19 #define DO16(buf) DO8(buf,0); DO8(buf,8);
20 
21 /* use NO_DIVIDE if your processor does not do division in hardware */
22 #ifdef NO_DIVIDE
23 # define MOD(a) \
24  do { \
25  if (a >= (BASE << 16)) a -= (BASE << 16); \
26  if (a >= (BASE << 15)) a -= (BASE << 15); \
27  if (a >= (BASE << 14)) a -= (BASE << 14); \
28  if (a >= (BASE << 13)) a -= (BASE << 13); \
29  if (a >= (BASE << 12)) a -= (BASE << 12); \
30  if (a >= (BASE << 11)) a -= (BASE << 11); \
31  if (a >= (BASE << 10)) a -= (BASE << 10); \
32  if (a >= (BASE << 9)) a -= (BASE << 9); \
33  if (a >= (BASE << 8)) a -= (BASE << 8); \
34  if (a >= (BASE << 7)) a -= (BASE << 7); \
35  if (a >= (BASE << 6)) a -= (BASE << 6); \
36  if (a >= (BASE << 5)) a -= (BASE << 5); \
37  if (a >= (BASE << 4)) a -= (BASE << 4); \
38  if (a >= (BASE << 3)) a -= (BASE << 3); \
39  if (a >= (BASE << 2)) a -= (BASE << 2); \
40  if (a >= (BASE << 1)) a -= (BASE << 1); \
41  if (a >= BASE) a -= BASE; \
42  } while (0)
43 # define MOD4(a) \
44  do { \
45  if (a >= (BASE << 4)) a -= (BASE << 4); \
46  if (a >= (BASE << 3)) a -= (BASE << 3); \
47  if (a >= (BASE << 2)) a -= (BASE << 2); \
48  if (a >= (BASE << 1)) a -= (BASE << 1); \
49  if (a >= BASE) a -= BASE; \
50  } while (0)
51 #else
52 # define MOD(a) a %= BASE
53 # define MOD4(a) a %= BASE
54 #endif
55 
56 /* ========================================================================= */
57 uLong ZEXPORT adler32(adler, buf, len)
58  uLong adler;
59  const Bytef *buf;
60  uInt len;
61 {
62  unsigned long sum2;
63  unsigned n;
64 
65  /* split Adler-32 into component sums */
66  sum2 = (adler >> 16) & 0xffff;
67  adler &= 0xffff;
68 
69  /* in case user likes doing a byte at a time, keep it fast */
70  if (len == 1) {
71  adler += buf[0];
72  if (adler >= BASE)
73  adler -= BASE;
74  sum2 += adler;
75  if (sum2 >= BASE)
76  sum2 -= BASE;
77  return adler | (sum2 << 16);
78  }
79 
80  /* initial Adler-32 value (deferred check for len == 1 speed) */
81  if (buf == Z_NULL)
82  return 1L;
83 
84  /* in case short lengths are provided, keep it somewhat fast */
85  if (len < 16) {
86  while (len--) {
87  adler += *buf++;
88  sum2 += adler;
89  }
90  if (adler >= BASE)
91  adler -= BASE;
92  MOD4(sum2); /* only added so many BASE's */
93  return adler | (sum2 << 16);
94  }
95 
96  /* do length NMAX blocks -- requires just one modulo operation */
97  while (len >= NMAX) {
98  len -= NMAX;
99  n = NMAX / 16; /* NMAX is divisible by 16 */
100  do {
101  DO16(buf); /* 16 sums unrolled */
102  buf += 16;
103  } while (--n);
104  MOD(adler);
105  MOD(sum2);
106  }
107 
108  /* do remaining bytes (less than NMAX, still just one modulo) */
109  if (len) { /* avoid modulos if none remaining */
110  while (len >= 16) {
111  len -= 16;
112  DO16(buf);
113  buf += 16;
114  }
115  while (len--) {
116  adler += *buf++;
117  sum2 += adler;
118  }
119  MOD(adler);
120  MOD(sum2);
121  }
122 
123  /* return recombined sums */
124  return adler | (sum2 << 16);
125 }
126 
127 /* ========================================================================= */
128 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
129  uLong adler1;
130  uLong adler2;
131  z_off_t len2;
132 {
133  unsigned long sum1;
134  unsigned long sum2;
135  unsigned rem;
136 
137  /* the derivation of this formula is left as an exercise for the reader */
138  rem = (unsigned)(len2 % BASE);
139  sum1 = adler1 & 0xffff;
140  sum2 = rem * sum1;
141  MOD(sum2);
142  sum1 += (adler2 & 0xffff) + BASE - 1;
143  sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
144  if (sum1 > BASE) sum1 -= BASE;
145  if (sum1 > BASE) sum1 -= BASE;
146  if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
147  if (sum2 > BASE) sum2 -= BASE;
148  return sum1 | (sum2 << 16);
149 }
Bytef
Byte FAR Bytef
Definition: zconf.h:270
DO16
#define DO16(buf)
Definition: adler32.c:19
uLong
unsigned long uLong
Definition: zconf.h:264
MOD
#define MOD(a)
Definition: adler32.c:52
autoplay.n
n
Definition: autoplay.py:12
BASE
#define BASE
Definition: adler32.c:11
z_off_t
#define z_off_t
Definition: zconf.h:301
NMAX
#define NMAX
Definition: adler32.c:12
Z_NULL
#define Z_NULL
Definition: zlib.h:205
buf
png_bytep buf
Definition: png.h:2726
ZEXPORT
#define ZEXPORT
Definition: zconf.h:250
uInt
unsigned int uInt
Definition: zconf.h:263
adler32
uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)
Definition: adler32.c:57
adler32_combine
uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2)
Definition: adler32.c:128
MOD4
#define MOD4(a)
Definition: adler32.c:53
zlib.h


openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Wed Sep 7 2022 02:51:02