FFmpeg
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 /**
25  * @file
26  * Computes the Adler-32 checksum of a data stream
27  *
28  * This is a modified version based on adler32.c from the zlib library.
29  * @author Mark Adler
30  * @ingroup lavu_adler32
31  */
32 
33 #include "config.h"
34 #include "adler32.h"
35 #include "common.h"
36 #include "intreadwrite.h"
37 
38 #define BASE 65521L /* largest prime smaller than 65536 */
39 
40 #define DO1(buf) { s1 += *buf++; s2 += s1; }
41 #define DO4(buf) DO1(buf); DO1(buf); DO1(buf); DO1(buf);
42 #define DO16(buf) DO4(buf); DO4(buf); DO4(buf); DO4(buf);
43 
44 unsigned long av_adler32_update(unsigned long adler, const uint8_t * buf,
45  unsigned int len)
46 {
47  unsigned long s1 = adler & 0xffff;
48  unsigned long s2 = adler >> 16;
49 
50  while (len > 0) {
51 #if HAVE_FAST_64BIT && HAVE_FAST_UNALIGNED && !CONFIG_SMALL
52  unsigned len2 = FFMIN((len-1) & ~7, 23*8);
53  if (len2) {
54  uint64_t a1= 0;
55  uint64_t a2= 0;
56  uint64_t b1= 0;
57  uint64_t b2= 0;
58  len -= len2;
59  s2 += s1*len2;
60  while (len2 >= 8) {
61  uint64_t v = AV_RN64(buf);
62  a2 += a1;
63  b2 += b1;
64  a1 += v &0x00FF00FF00FF00FF;
65  b1 += (v>>8)&0x00FF00FF00FF00FF;
66  len2 -= 8;
67  buf+=8;
68  }
69 
70  //We combine the 8 interleaved adler32 checksums without overflows
71  //Decreasing the number of iterations would allow below code to be
72  //simplified but would likely be slower due to the fewer iterations
73  //of the inner loop
74  s1 += ((a1+b1)*0x1000100010001)>>48;
75  s2 += ((((a2&0xFFFF0000FFFF)+(b2&0xFFFF0000FFFF)+((a2>>16)&0xFFFF0000FFFF)+((b2>>16)&0xFFFF0000FFFF))*0x800000008)>>32)
76 #if HAVE_BIGENDIAN
77  + 2*((b1*0x1000200030004)>>48)
78  + ((a1*0x1000100010001)>>48)
79  + 2*((a1*0x0000100020003)>>48);
80 #else
81  + 2*((a1*0x4000300020001)>>48)
82  + ((b1*0x1000100010001)>>48)
83  + 2*((b1*0x3000200010000)>>48);
84 #endif
85  }
86 #else
87  while (len > 4 && s2 < (1U << 31)) {
88  DO4(buf);
89  len -= 4;
90  }
91 #endif
92  DO1(buf); len--;
93  s1 %= BASE;
94  s2 %= BASE;
95  }
96  return (s2 << 16) | s1;
97 }
#define BASE
Definition: adler32.c:38
#define a1
Definition: regdef.h:47
uint8_t
#define DO4(buf)
Definition: adler32.c:41
unsigned long av_adler32_update(unsigned long adler, const uint8_t *buf, unsigned int len)
Calculate the Adler32 checksum of a buffer.
Definition: adler32.c:44
#define U(x)
Definition: vp56_arith.h:37
#define s2
Definition: regdef.h:39
#define FFMIN(a, b)
Definition: common.h:96
#define a2
Definition: regdef.h:48
Public header for Adler-32 hash function implementation.
void * buf
Definition: avisynth_c.h:766
#define s1
Definition: regdef.h:38
common internal and external API header
#define DO1(buf)
Definition: adler32.c:40
int len
#define AV_RN64(p)
Definition: intreadwrite.h:368