static void adx_encode(unsigned char *adx,const short *wav,
                       ADXChannelState *prev)
{
    int scale;
    int i;
    int s0,s1,s2,d;
    int max=0;
    int min=0;
    int data[32];

    s1 = prev->s1;
    s2 = prev->s2;
    for(i=0;i<32;i++) {
        s0 = wav[i];
        d = ((s0<<14) - SCALE1*s1 + SCALE2*s2)/BASEVOL;
        data[i]=d;
        if (max<d) max=d;
        if (min>d) min=d;
        s2 = s1;
        s1 = s0;
    }
    prev->s1 = s1;
    prev->s2 = s2;

    /* -8..+7 */

    if (max==0 && min==0) {
        memset(adx,0,18);
        return;
    }

    if (max/7>-min/8) scale = max/7;
    else scale = -min/8;

    if (scale==0) scale=1;

    AV_WB16(adx, scale);

    for(i=0;i<16;i++) {
        adx[i+2] = ((data[i*2]/scale)<<4) | ((data[i*2+1]/scale)&0xf);
    }
}