modules/audio_coding/codecs/isac/fix/source/lattice_c.c

/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

/*
 * Contains the core loop function for the lattice filter AR routine
 * for iSAC codec.
 *
 */

#include "settings.h"
#include "signal_processing_library.h"
#include "webrtc/typedefs.h"

/* Filter ar_g_Q0[] and ar_f_Q0[] through an AR filter with coefficients
 * cth_Q15[] and sth_Q15[].
 */
void WebRtcIsacfix_FilterArLoop(int16_t* ar_g_Q0,     // Input samples
                                int16_t* ar_f_Q0,     // Input samples
                                int16_t* cth_Q15,     // Filter coefficients
                                int16_t* sth_Q15,     // Filter coefficients
                                size_t order_coef) { // order of the filter
  int n = 0;

  for (n = 0; n < HALF_SUBFRAMELEN - 1; n++) {
    size_t k = 0;
    int16_t tmpAR = 0;
    int32_t tmp32 = 0;
    int32_t tmp32_2 = 0;

    tmpAR = ar_f_Q0[n + 1];
    for (k = order_coef; k > 0; k--) {
      tmp32 = (cth_Q15[k - 1] * tmpAR - sth_Q15[k - 1] * ar_g_Q0[k - 1] +
               16384) >> 15;
      tmp32_2 = (sth_Q15[k - 1] * tmpAR + cth_Q15[k - 1] * ar_g_Q0[k - 1] +
                 16384) >> 15;
      tmpAR   = (int16_t)WebRtcSpl_SatW32ToW16(tmp32);
      ar_g_Q0[k] = (int16_t)WebRtcSpl_SatW32ToW16(tmp32_2);
    }
    ar_f_Q0[n + 1] = tmpAR;
    ar_g_Q0[0] = tmpAR;
  }
}