DSP/Source/FilteringFunctions/arm_biquad_cascade_df2T_init_f32.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_biquad_cascade_df2T_init_f32.c
 * Description:  Initialization function for floating-point transposed direct form II Biquad cascade filter
 *
 * $Date:        18. March 2019
 * $Revision:    V1.6.0
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "arm_math.h"

/**
  @ingroup groupFilters
 */

/**
  @addtogroup BiquadCascadeDF2T
  @{
 */

/**
  @brief         Initialization function for the floating-point transposed direct form II Biquad cascade filter.
  @param[in,out] S           points to an instance of the filter data structure.
  @param[in]     numStages   number of 2nd order stages in the filter.
  @param[in]     pCoeffs     points to the filter coefficients.
  @param[in]     pState      points to the state buffer.
  @return        none

  @par           Coefficient and State Ordering
                   The coefficients are stored in the array <code>pCoeffs</code> in the following order
                   in the not Neon version.
  <pre>
      {b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
  </pre>
                   
  @par
                   where <code>b1x</code> and <code>a1x</code> are the coefficients for the first stage,
                   <code>b2x</code> and <code>a2x</code> are the coefficients for the second stage,
                   and so on.  The <code>pCoeffs</code> array contains a total of <code>5*numStages</code> values.

                   For Neon version, this array is bigger. If numstages = 4x + y, then the array has size:
                   32*x + 5*y
                   and it must be initialized using the function
                   arm_biquad_cascade_df2T_compute_coefs_f32 which is taking the
                   standard array coefficient as parameters.

                   But, an array of 8*numstages is a good approximation.

                   Then, the initialization can be done with:
  <pre>
                   arm_biquad_cascade_df2T_init_f32(&SNeon, nbCascade, neonCoefs, stateNeon);
                   arm_biquad_cascade_df2T_compute_coefs_f32(&SNeon,nbCascade,coefs);
  </pre>

  @par             In this example, neonCoefs is a bigger array of size 8 * numStages.
                   coefs is the standard array:

  <pre>
      {b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
  </pre>


  @par
                   The <code>pState</code> is a pointer to state array.
                   Each Biquad stage has 2 state variables <code>d1,</code> and <code>d2</code>.
                   The 2 state variables for stage 1 are first, then the 2 state variables for stage 2, and so on.
                   The state array has a total length of <code>2*numStages</code> values.
                   The state variables are updated after each block of data is processed; the coefficients are untouched.
 */

#if defined(ARM_MATH_NEON) 
/*

Must be called after initializing the biquad instance.
pCoeffs has size 5 * nbCascade
Whereas the pCoeffs for the init has size (4*4 + 4*4)* nbCascade 

So this pCoeffs is the one which would be used for the not Neon version.
The pCoeffs passed in init is bigger than the one for the not Neon version.

*/
void arm_biquad_cascade_df2T_compute_coefs_f32(
  arm_biquad_cascade_df2T_instance_f32 * S,
  uint8_t numStages,
  float32_t * pCoeffs)
{
   uint8_t cnt;
   float32_t *pDstCoeffs;
   float32_t b0[4],b1[4],b2[4],a1[4],a2[4];

   pDstCoeffs = S->pCoeffs;

   cnt = numStages >> 2; 
   while(cnt > 0)
   {
      for(int i=0;i<4;i++)
      {
        b0[i] = pCoeffs[0];
        b1[i] = pCoeffs[1];
        b2[i] = pCoeffs[2];
        a1[i] = pCoeffs[3];
        a2[i] = pCoeffs[4];
        pCoeffs += 5;
      }

      /* Vec 1 */
      *pDstCoeffs++ = 0;
      *pDstCoeffs++ = b0[1];
      *pDstCoeffs++ = b0[2];
      *pDstCoeffs++ = b0[3];

      /* Vec 2 */
      *pDstCoeffs++ = 0;
      *pDstCoeffs++ = 0;
      *pDstCoeffs++ = b0[1] * b0[2];
      *pDstCoeffs++ = b0[2] * b0[3];

      /* Vec 3 */
      *pDstCoeffs++ = 0;
      *pDstCoeffs++ = 0;
      *pDstCoeffs++ = 0;
      *pDstCoeffs++ = b0[1] * b0[2] * b0[3];
      
      /* Vec 4 */
      *pDstCoeffs++ = b0[0];
      *pDstCoeffs++ = b0[0] * b0[1];
      *pDstCoeffs++ = b0[0] * b0[1] * b0[2];
      *pDstCoeffs++ = b0[0] * b0[1] * b0[2] * b0[3];

      /* Vec 5 */
      *pDstCoeffs++ = b1[0];
      *pDstCoeffs++ = b1[1];
      *pDstCoeffs++ = b1[2];
      *pDstCoeffs++ = b1[3];

      /* Vec 6 */
      *pDstCoeffs++ = b2[0];
      *pDstCoeffs++ = b2[1];
      *pDstCoeffs++ = b2[2];
      *pDstCoeffs++ = b2[3];

      /* Vec 7 */
      *pDstCoeffs++ = a1[0];
      *pDstCoeffs++ = a1[1];
      *pDstCoeffs++ = a1[2];
      *pDstCoeffs++ = a1[3];

      /* Vec 8 */
      *pDstCoeffs++ = a2[0];
      *pDstCoeffs++ = a2[1];
      *pDstCoeffs++ = a2[2];
      *pDstCoeffs++ = a2[3];

      cnt--;
   }

   cnt = numStages & 0x3;
   while(cnt > 0)
   {
      *pDstCoeffs++ = *pCoeffs++;
      *pDstCoeffs++ = *pCoeffs++;
      *pDstCoeffs++ = *pCoeffs++;
      *pDstCoeffs++ = *pCoeffs++;
      *pDstCoeffs++ = *pCoeffs++;
      cnt--;
   }

}
#endif 

void arm_biquad_cascade_df2T_init_f32(
        arm_biquad_cascade_df2T_instance_f32 * S,
        uint8_t numStages,
  const float32_t * pCoeffs,
        float32_t * pState)
{
  /* Assign filter stages */
  S->numStages = numStages;

  /* Assign coefficient pointer */
  S->pCoeffs = pCoeffs;

  /* Clear state buffer and size is always 2 * numStages */
  memset(pState, 0, (2U * (uint32_t) numStages) * sizeof(float32_t));

  /* Assign state pointer */
  S->pState = pState;
}

/**
  @} end of BiquadCascadeDF2T group
 */