codec.c

来自「linux下的sip voip程序」· C语言 代码 · 共 54 行

#include <stdio.h>
#include "codec.h"

unsigned char g711encode2(short audio_sample){
    static short i = -32768;
    if (i>=32000){
        i=-32000;
    }else{
        i+=100;
    }   
    return g711encode(i);
}
unsigned char g711encode(short audio_sample){
    int i;
    int mask;
    int range;
    unsigned char mulaw_val;
    
    if ( audio_sample > 0 && audio_sample > CLIP ) audio_sample = CLIP;
    if ( audio_sample < 0 && audio_sample < -CLIP ) audio_sample = -CLIP;
    if ( audio_sample < 0 ){
        mask = 0x7f;
        audio_sample = -audio_sample;
    }else{
        mask = 0xff;
    }
    
    audio_sample += BIAS;
    for ( i = 7, range = 0x4000; range >= 0x80; range >>= 1, i-- ){
        if ( range & audio_sample ) break;
    }
    mulaw_val =  (i << 4) +  ( ( audio_sample >> ( i + 3 ) ) & 0x0f);

    return mulaw_val ^ mask;
}

short g711decode2(unsigned char ulaw_sample){
    return ulaw_sample<<8;
}

short g711decode(unsigned char ulaw_sample){
    short audio_sample;
    int t;
    
    ulaw_sample = ~ulaw_sample;

    t = ((ulaw_sample & 0x0f) << 3) + BIAS;
    t <<= (ulaw_sample & 0x70) >> 4;

    audio_sample = ((ulaw_sample & 0x80) ? (BIAS - t) : (t - BIAS));

    return audio_sample;
}