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adler32.c
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1 /*
2  * Compute the Adler-32 checksum of a data stream.
3  * This is a modified version based on adler32.c from the zlib library.
4  *
5  * Copyright (C) 1995 Mark Adler
6  *
7  * This software is provided 'as-is', without any express or implied
8  * warranty. In no event will the authors be held liable for any damages
9  * arising from the use of this software.
10  *
11  * Permission is granted to anyone to use this software for any purpose,
12  * including commercial applications, and to alter it and redistribute it
13  * freely, subject to the following restrictions:
14  *
15  * 1. The origin of this software must not be misrepresented; you must not
16  * claim that you wrote the original software. If you use this software
17  * in a product, an acknowledgment in the product documentation would be
18  * appreciated but is not required.
19  * 2. Altered source versions must be plainly marked as such, and must not be
20  * misrepresented as being the original software.
21  * 3. This notice may not be removed or altered from any source distribution.
22  */
23 
24 #include "config.h"
25 #include "adler32.h"
26 #include "common.h"
27 #include "intreadwrite.h"
28 
29 #define BASE 65521L /* largest prime smaller than 65536 */
30 
31 #define DO1(buf) { s1 += *buf++; s2 += s1; }
32 #define DO4(buf) DO1(buf); DO1(buf); DO1(buf); DO1(buf);
33 #define DO16(buf) DO4(buf); DO4(buf); DO4(buf); DO4(buf);
34 
35 unsigned long av_adler32_update(unsigned long adler, const uint8_t * buf,
36  unsigned int len)
37 {
38  unsigned long s1 = adler & 0xffff;
39  unsigned long s2 = adler >> 16;
40 
41  while (len > 0) {
42 #if HAVE_FAST_64BIT && HAVE_FAST_UNALIGNED && !CONFIG_SMALL
43  unsigned len2 = FFMIN((len-1) & ~7, 23*8);
44  if (len2) {
45  uint64_t a1= 0;
46  uint64_t a2= 0;
47  uint64_t b1= 0;
48  uint64_t b2= 0;
49  len -= len2;
50  s2 += s1*len2;
51  while (len2 >= 8) {
52  uint64_t v = AV_RN64(buf);
53  a2 += a1;
54  b2 += b1;
55  a1 += v &0x00FF00FF00FF00FF;
56  b1 += (v>>8)&0x00FF00FF00FF00FF;
57  len2 -= 8;
58  buf+=8;
59  }
60 
61  //We combine the 8 interleaved adler32 checksums without overflows
62  //Decreasing the number of iterations would allow below code to be
63  //simplified but would likely be slower due to the fewer iterations
64  //of the inner loop
65  s1 += ((a1+b1)*0x1000100010001)>>48;
66  s2 += ((((a2&0xFFFF0000FFFF)+(b2&0xFFFF0000FFFF)+((a2>>16)&0xFFFF0000FFFF)+((b2>>16)&0xFFFF0000FFFF))*0x800000008)>>32)
67 #if HAVE_BIGENDIAN
68  + 2*((b1*0x1000200030004)>>48)
69  + ((a1*0x1000100010001)>>48)
70  + 2*((a1*0x0000100020003)>>48);
71 #else
72  + 2*((a1*0x4000300020001)>>48)
73  + ((b1*0x1000100010001)>>48)
74  + 2*((b1*0x3000200010000)>>48);
75 #endif
76  }
77 #else
78  while (len > 4 && s2 < (1U << 31)) {
79  DO4(buf);
80  len -= 4;
81  }
82 #endif
83  DO1(buf); len--;
84  s1 %= BASE;
85  s2 %= BASE;
86  }
87  return (s2 << 16) | s1;
88 }
89 
90 #ifdef TEST
91 // LCOV_EXCL_START
92 #include <string.h>
93 #include "log.h"
94 #include "timer.h"
95 #define LEN 7001
96 
97 static volatile int checksum;
98 
99 int main(int argc, char **argv)
100 {
101  int i;
102  char data[LEN];
103 
105 
106  for (i = 0; i < LEN; i++)
107  data[i] = ((i * i) >> 3) + 123 * i;
108 
109  if (argc > 1 && !strcmp(argv[1], "-t")) {
110  for (i = 0; i < 1000; i++) {
111  START_TIMER;
112  checksum = av_adler32_update(1, data, LEN);
113  STOP_TIMER("adler");
114  }
115  } else {
116  checksum = av_adler32_update(1, data, LEN);
117  }
118 
119  av_log(NULL, AV_LOG_DEBUG, "%X (expected 50E6E508)\n", checksum);
120  return checksum == 0x50e6e508 ? 0 : 1;
121 }
122 // LCOV_EXCL_STOP
123 #endif