static void alac_linear_predictor(AlacEncodeContext *s, int ch)

{

    int i;

    LPCContext lpc = s->lpc[ch];



    if(lpc.lpc_order == 31) {

        s->predictor_buf[0] = s->sample_buf[ch][0];



        for(i=1; i<s->avctx->frame_size; i++)

            s->predictor_buf[i] = s->sample_buf[ch][i] - s->sample_buf[ch][i-1];



        return;

    }



    // generalised linear predictor



    if(lpc.lpc_order > 0) {

        int32_t *samples  = s->sample_buf[ch];

        int32_t *residual = s->predictor_buf;



        // generate warm-up samples

        residual[0] = samples[0];

        for(i=1;i<=lpc.lpc_order;i++)

            residual[i] = samples[i] - samples[i-1];



        // perform lpc on remaining samples

        for(i = lpc.lpc_order + 1; i < s->avctx->frame_size; i++) {

            int sum = 1 << (lpc.lpc_quant - 1), res_val, j;



            for (j = 0; j < lpc.lpc_order; j++) {

                sum += (samples[lpc.lpc_order-j] - samples[0]) *

                        lpc.lpc_coeff[j];

            }



            sum >>= lpc.lpc_quant;

            sum += samples[0];

            residual[i] = samples[lpc.lpc_order+1] - sum;

            res_val = residual[i];



            if(res_val) {

                int index = lpc.lpc_order - 1;

                int neg = (res_val < 0);



                while(index >= 0 && (neg ? (res_val < 0):(res_val > 0))) {

                    int val = samples[0] - samples[lpc.lpc_order - index];

                    int sign = (val ? FFSIGN(val) : 0);



                    if(neg)

                        sign*=-1;



                    lpc.lpc_coeff[index] -= sign;

                    val *= sign;

                    res_val -= ((val >> lpc.lpc_quant) *

                            (lpc.lpc_order - index));

                    index--;

                }

            }

            samples++;

        }

    }

}
