98 lines
3.3 KiB
C
98 lines
3.3 KiB
C
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/*
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* Compute the Adler-32 checksum of a data stream.
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* This is a modified version based on adler32.c from the zlib library.
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*
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* Copyright (C) 1995 Mark Adler
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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/**
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* @file
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* Computes the Adler-32 checksum of a data stream
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*
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* This is a modified version based on adler32.c from the zlib library.
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* @author Mark Adler
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* @ingroup lavu_adler32
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*/
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#include "config.h"
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#include "adler32.h"
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#include "common.h"
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#include "intreadwrite.h"
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#define BASE 65521L /* largest prime smaller than 65536 */
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#define DO1(buf) { s1 += *buf++; s2 += s1; }
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#define DO4(buf) DO1(buf); DO1(buf); DO1(buf); DO1(buf);
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#define DO16(buf) DO4(buf); DO4(buf); DO4(buf); DO4(buf);
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unsigned long av_adler32_update(unsigned long adler, const uint8_t * buf,
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unsigned int len)
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{
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unsigned long s1 = adler & 0xffff;
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unsigned long s2 = adler >> 16;
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while (len > 0) {
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#if HAVE_FAST_64BIT && HAVE_FAST_UNALIGNED && !CONFIG_SMALL
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unsigned len2 = FFMIN((len-1) & ~7, 23*8);
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if (len2) {
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uint64_t a1= 0;
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uint64_t a2= 0;
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uint64_t b1= 0;
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uint64_t b2= 0;
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len -= len2;
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s2 += s1*len2;
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while (len2 >= 8) {
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uint64_t v = AV_RN64(buf);
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a2 += a1;
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b2 += b1;
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a1 += v &0x00FF00FF00FF00FF;
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b1 += (v>>8)&0x00FF00FF00FF00FF;
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len2 -= 8;
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buf+=8;
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}
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//We combine the 8 interleaved adler32 checksums without overflows
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//Decreasing the number of iterations would allow below code to be
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//simplified but would likely be slower due to the fewer iterations
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//of the inner loop
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s1 += ((a1+b1)*0x1000100010001)>>48;
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s2 += ((((a2&0xFFFF0000FFFF)+(b2&0xFFFF0000FFFF)+((a2>>16)&0xFFFF0000FFFF)+((b2>>16)&0xFFFF0000FFFF))*0x800000008)>>32)
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#if HAVE_BIGENDIAN
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+ 2*((b1*0x1000200030004)>>48)
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+ ((a1*0x1000100010001)>>48)
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+ 2*((a1*0x0000100020003)>>48);
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#else
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+ 2*((a1*0x4000300020001)>>48)
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+ ((b1*0x1000100010001)>>48)
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+ 2*((b1*0x3000200010000)>>48);
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#endif
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}
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#else
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while (len > 4 && s2 < (1U << 31)) {
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DO4(buf);
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len -= 4;
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}
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#endif
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DO1(buf); len--;
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s1 %= BASE;
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s2 %= BASE;
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}
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return (s2 << 16) | s1;
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}
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