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++; } } }