src/modules/audio_coding/codecs/iSAC/fix/source/filters.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.
 */

/*
 * filters.c
 *
 * This file contains function WebRtcIsacfix_AutocorrC,
 * AllpassFilterForDec32, and WebRtcIsacfix_DecimateAllpass32
 *
 */

#include <string.h>

#include "pitch_estimator.h"
#include "lpc_masking_model.h"
#include "codec.h"

// Autocorrelation function in fixed point.
// NOTE! Different from SPLIB-version in how it scales the signal.
int WebRtcIsacfix_AutocorrC(WebRtc_Word32* __restrict r,
                            const WebRtc_Word16* __restrict x,
                            WebRtc_Word16 N,
                            WebRtc_Word16 order,
                            WebRtc_Word16* __restrict scale) {
  int i = 0;
  int j = 0;
  int16_t scaling = 0;
  int32_t sum = 0;
  uint32_t temp = 0;
  int64_t prod = 0;

  // Calculate r[0].
  for (i = 0; i < N; i++) {
    prod += WEBRTC_SPL_MUL_16_16(x[i], x[i]);
  }

  // Calculate scaling (the value of shifting).
  temp = (uint32_t)(prod >> 31);
  if(temp == 0) {
    scaling = 0;
  } else {
    scaling = 32 - WebRtcSpl_NormU32(temp);
  }
  r[0] = (int32_t)(prod >> scaling);

  // Perform the actual correlation calculation.
  for (i = 1; i < order + 1; i++) {
    prod = 0;
    for (j = 0; j < N - i; j++) {
      prod += WEBRTC_SPL_MUL_16_16(x[j], x[i + j]);
    }
    sum = (int32_t)(prod >> scaling);
    r[i] = sum;
  }

  *scale = scaling;

  return(order + 1);
}

static const WebRtc_Word32 kApUpperQ15[ALLPASSSECTIONS] = { 1137, 12537 };
static const WebRtc_Word32 kApLowerQ15[ALLPASSSECTIONS] = { 5059, 24379 };


static void AllpassFilterForDec32(WebRtc_Word16         *InOut16, //Q0
                                  const WebRtc_Word32   *APSectionFactors, //Q15
                                  WebRtc_Word16         lengthInOut,
                                  WebRtc_Word32          *FilterState) //Q16
{
  int n, j;
  WebRtc_Word32 a, b;

  for (j=0; j<ALLPASSSECTIONS; j++) {
    for (n=0;n<lengthInOut;n+=2){
      a = WEBRTC_SPL_MUL_16_32_RSFT16(InOut16[n], APSectionFactors[j]); //Q0*Q31=Q31 shifted 16 gives Q15
      a = WEBRTC_SPL_LSHIFT_W32(a, 1); // Q15 -> Q16
      b = WEBRTC_SPL_ADD_SAT_W32(a, FilterState[j]); //Q16+Q16=Q16
      a = WEBRTC_SPL_MUL_16_32_RSFT16(
          (WebRtc_Word16) WEBRTC_SPL_RSHIFT_W32(b, 16),
          -APSectionFactors[j]); //Q0*Q31=Q31 shifted 16 gives Q15
      FilterState[j] = WEBRTC_SPL_ADD_SAT_W32(
          WEBRTC_SPL_LSHIFT_W32(a,1),
          WEBRTC_SPL_LSHIFT_W32((WebRtc_UWord32)InOut16[n], 16)); // Q15<<1 + Q0<<16 = Q16 + Q16 = Q16
      InOut16[n] = (WebRtc_Word16) WEBRTC_SPL_RSHIFT_W32(b, 16); //Save as Q0
    }
  }
}




void WebRtcIsacfix_DecimateAllpass32(const WebRtc_Word16 *in,
                                     WebRtc_Word32 *state_in,        /* array of size: 2*ALLPASSSECTIONS+1 */
                                     WebRtc_Word16 N,                /* number of input samples */
                                     WebRtc_Word16 *out)             /* array of size N/2 */
{
  int n;
  WebRtc_Word16 data_vec[PITCH_FRAME_LEN];

  /* copy input */
  memcpy(data_vec+1, in, WEBRTC_SPL_MUL_16_16(sizeof(WebRtc_Word16), (N-1)));


  data_vec[0] = (WebRtc_Word16) WEBRTC_SPL_RSHIFT_W32(state_in[WEBRTC_SPL_MUL_16_16(2, ALLPASSSECTIONS)],16);   //the z^(-1) state
  state_in[WEBRTC_SPL_MUL_16_16(2, ALLPASSSECTIONS)] = WEBRTC_SPL_LSHIFT_W32((WebRtc_UWord32)in[N-1],16);



  AllpassFilterForDec32(data_vec+1, kApUpperQ15, N, state_in);
  AllpassFilterForDec32(data_vec, kApLowerQ15, N, state_in+ALLPASSSECTIONS);

  for (n=0;n<N/2;n++) {
    out[n]=WEBRTC_SPL_ADD_SAT_W16(data_vec[WEBRTC_SPL_MUL_16_16(2, n)], data_vec[WEBRTC_SPL_MUL_16_16(2, n)+1]);
  }
}