adler32.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

/* adler32.c -- 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.
 */

#include "common.h"
#include "adler32.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) {
#ifdef CONFIG_SMALL
        while(len>4 && s2 < (1U<<31)){
            DO4(buf); len-=4;
#else
        while(len>16 && s2 < (1U<<31)){
            DO16(buf); len-=16;
#endif
        }
        DO1(buf); len--;
        s1 %= BASE;
        s2 %= BASE;
    }
    return (s2 << 16) | s1;
}

#ifdef TEST
#include "log.h"
#define LEN 7001
volatile int checksum;
int main(){
    int i;
    char data[LEN];
    av_log_level = AV_LOG_DEBUG;
    for(i=0; i<LEN; i++)
        data[i]= ((i*i)>>3) + 123*i;
    for(i=0; i<1000; i++){
        START_TIMER
        checksum= av_adler32_update(1, data, LEN);
        STOP_TIMER("adler")
    }
    av_log(NULL, AV_LOG_DEBUG, "%X == 50E6E508\n", checksum);
}
#endif