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libavutil/adler32.c

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00001 /*
00002  * Compute the Adler-32 checksum of a data stream.
00003  * This is a modified version based on adler32.c from the zlib library.
00004  *
00005  * Copyright (C) 1995 Mark Adler
00006  *
00007  * This software is provided 'as-is', without any express or implied
00008  * warranty.  In no event will the authors be held liable for any damages
00009  * arising from the use of this software.
00010  *
00011  * Permission is granted to anyone to use this software for any purpose,
00012  * including commercial applications, and to alter it and redistribute it
00013  * freely, subject to the following restrictions:
00014  *
00015  * 1. The origin of this software must not be misrepresented; you must not
00016  *    claim that you wrote the original software. If you use this software
00017  *    in a product, an acknowledgment in the product documentation would be
00018  *    appreciated but is not required.
00019  * 2. Altered source versions must be plainly marked as such, and must not be
00020  *    misrepresented as being the original software.
00021  * 3. This notice may not be removed or altered from any source distribution.
00022  */
00023 
00024 #include "config.h"
00025 #include "adler32.h"
00026 
00027 #define BASE 65521L /* largest prime smaller than 65536 */
00028 
00029 #define DO1(buf)  {s1 += *buf++; s2 += s1;}
00030 #define DO4(buf)  DO1(buf); DO1(buf); DO1(buf); DO1(buf);
00031 #define DO16(buf) DO4(buf); DO4(buf); DO4(buf); DO4(buf);
00032 
00033 unsigned long av_adler32_update(unsigned long adler, const uint8_t *buf, unsigned int len)
00034 {
00035     unsigned long s1 = adler & 0xffff;
00036     unsigned long s2 = adler >> 16;
00037 
00038     while (len>0) {
00039 #if CONFIG_SMALL
00040         while(len>4 && s2 < (1U<<31)){
00041             DO4(buf); len-=4;
00042 #else
00043         while(len>16 && s2 < (1U<<31)){
00044             DO16(buf); len-=16;
00045 #endif
00046         }
00047         DO1(buf); len--;
00048         s1 %= BASE;
00049         s2 %= BASE;
00050     }
00051     return (s2 << 16) | s1;
00052 }
00053 
00054 #ifdef TEST
00055 #include "log.h"
00056 #include "timer.h"
00057 #define LEN 7001
00058 volatile int checksum;
00059 int main(void){
00060     int i;
00061     char data[LEN];
00062     av_log_set_level(AV_LOG_DEBUG);
00063     for(i=0; i<LEN; i++)
00064         data[i]= ((i*i)>>3) + 123*i;
00065     for(i=0; i<1000; i++){
00066         START_TIMER
00067         checksum= av_adler32_update(1, data, LEN);
00068         STOP_TIMER("adler")
00069     }
00070     av_log(NULL, AV_LOG_DEBUG, "%X == 50E6E508\n", checksum);
00071     return 0;
00072 }
00073 #endif

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