#### Source code

#### Revision control

#### Copy as Markdown

#### Other Tools

```
/*
```

```
* Compute the Adler-32 checksum of a data stream.
```

```
* This is a modified version based on adler32.c from the zlib library.
```

```
*
```

```
* Copyright (C) 1995 Mark Adler
```

```
*
```

```
* This software is provided 'as-is', without any express or implied
```

```
* warranty. In no event will the authors be held liable for any damages
```

```
* arising from the use of this software.
```

```
*
```

```
* Permission is granted to anyone to use this software for any purpose,
```

```
* including commercial applications, and to alter it and redistribute it
```

```
* freely, subject to the following restrictions:
```

```
*
```

```
* 1. The origin of this software must not be misrepresented; you must not
```

```
* claim that you wrote the original software. If you use this software
```

```
* in a product, an acknowledgment in the product documentation would be
```

```
* appreciated but is not required.
```

```
* 2. Altered source versions must be plainly marked as such, and must not be
```

```
* misrepresented as being the original software.
```

```
* 3. This notice may not be removed or altered from any source distribution.
```

```
*/
```

```
```

```
/**
```

```
* @file
```

```
* Computes the Adler-32 checksum of a data stream
```

```
*
```

```
* This is a modified version based on adler32.c from the zlib library.
```

```
* @author Mark Adler
```

```
* @ingroup lavu_adler32
```

```
*/
```

```
```

```
#include "config.h"
```

```
#include "adler32.h"
```

```
#include "intreadwrite.h"
```

```
#include "macros.h"
```

```
```

```
#define BASE 65521L /* largest prime smaller than 65536 */
```

```
```

```
#define DO1(buf) { s1 += *buf++; s2 += s1; }
```

```
#define DO4(buf) DO1(buf); DO1(buf); DO1(buf); DO1(buf);
```

```
#define DO16(buf) DO4(buf); DO4(buf); DO4(buf); DO4(buf);
```

```
```

```
AVAdler av_adler32_update(AVAdler adler, const uint8_t *buf, size_t len)
```

```
{
```

```
unsigned long s1 = adler & 0xffff;
```

```
unsigned long s2 = adler >> 16;
```

```
```

```
while (len > 0) {
```

```
#if HAVE_FAST_64BIT && HAVE_FAST_UNALIGNED && !CONFIG_SMALL
```

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

```
if (len2) {
```

```
uint64_t a1= 0;
```

```
uint64_t a2= 0;
```

```
uint64_t b1= 0;
```

```
uint64_t b2= 0;
```

```
len -= len2;
```

```
s2 += s1*len2;
```

```
while (len2 >= 8) {
```

```
uint64_t v = AV_RN64(buf);
```

```
a2 += a1;
```

```
b2 += b1;
```

```
a1 += v &0x00FF00FF00FF00FF;
```

```
b1 += (v>>8)&0x00FF00FF00FF00FF;
```

```
len2 -= 8;
```

```
buf+=8;
```

```
}
```

```
```

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

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

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

```
//of the inner loop
```

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

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

```
#if HAVE_BIGENDIAN
```

```
+ 2*((b1*0x1000200030004)>>48)
```

```
+ ((a1*0x1000100010001)>>48)
```

```
+ 2*((a1*0x0000100020003)>>48);
```

```
#else
```

```
+ 2*((a1*0x4000300020001)>>48)
```

```
+ ((b1*0x1000100010001)>>48)
```

```
+ 2*((b1*0x3000200010000)>>48);
```

```
#endif
```

```
}
```

```
#else
```

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

```
DO4(buf);
```

```
len -= 4;
```

```
}
```

```
#endif
```

```
DO1(buf); len--;
```

```
s1 %= BASE;
```

```
s2 %= BASE;
```

```
}
```

```
return (s2 << 16) | s1;
```

```
}
```