FFmpeg: libavutil/adler32.c Source File

adler32.c

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 "intreadwrite.h"

36 #include "macros.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  AVAdler av_adler32_update(AVAdler adler, const uint8_t *buf, size_t len)

45 {

46  unsigned long s1 = adler & 0xffff;

47  unsigned long s2 = adler >> 16;

48 

49  while (len > 0) {

50 #if HAVE_FAST_64BIT && HAVE_FAST_UNALIGNED && !CONFIG_SMALL

51  unsigned len2 = FFMIN((len-1) & ~7, 23*8);

52  if (len2) {

53  uint64_t a1= 0;

54  uint64_t a2= 0;

55  uint64_t b1= 0;

56  uint64_t b2= 0;

57  len -= len2;

58  s2 += s1*len2;

59  while (len2 >= 8) {

60  uint64_t v = AV_RN64(buf);

61  a2 += a1;

62  b2 += b1;

63  a1 += v &0x00FF00FF00FF00FF;

64  b1 += (v>>8)&0x00FF00FF00FF00FF;

65  len2 -= 8;

66  buf+=8;

67  }

68 

69  //We combine the 8 interleaved adler32 checksums without overflows

70  //Decreasing the number of iterations would allow below code to be

71  //simplified but would likely be slower due to the fewer iterations

72  //of the inner loop

73  s1 += ((a1+b1)*0x1000100010001)>>48;

74  s2 += ((((a2&0xFFFF0000FFFF)+(b2&0xFFFF0000FFFF)+((a2>>16)&0xFFFF0000FFFF)+((b2>>16)&0xFFFF0000FFFF))*0x800000008)>>32)

75 #if HAVE_BIGENDIAN

76  + 2*((b1*0x1000200030004)>>48)

77  + ((a1*0x1000100010001)>>48)

78  + 2*((a1*0x0000100020003)>>48);

79 #else

80  + 2*((a1*0x4000300020001)>>48)

81  + ((b1*0x1000100010001)>>48)

82  + 2*((b1*0x3000200010000)>>48);

83 #endif

84  }

85 #else

86  while (len > 4 && s2 < (1U << 31)) {

87  DO4(buf);

88  len -= 4;

89  }

90 #endif

91  DO1(buf); len--;

92  s1 %= BASE;

93  s2 %= BASE;

94  }

95  return (s2 << 16) | s1;

96 }