aac5773f
 hucm
功能基本完成，接口待打磨
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/*
* 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 "common.h"
#include "intreadwrite.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);
unsigned long av_adler32_update(unsigned long adler, const uint8_t * buf,
unsigned int 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;
}
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