media/ffvpx/libavutil/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 }