DSP/Source/FilteringFunctions/arm_fir_decimate_init_q31.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_fir_decimate_init_q31.c
 * Description:  Initialization function for Q31 FIR Decimation filter
 *
 * $Date:        27. January 2017
 * $Revision:    V.1.5.1
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2017 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 FIR_decimate
 * @{
 */

/**
 * @brief  Initialization function for the Q31 FIR decimator.
 * @param[in,out] *S points to an instance of the Q31 FIR decimator structure.
 * @param[in] numTaps  number of coefficients in the filter.
 * @param[in] M  decimation factor.
 * @param[in] *pCoeffs points to the filter coefficients.
 * @param[in] *pState points to the state buffer.
 * @param[in] blockSize number of input samples to process per call.
 * @return    The function returns ARM_MATH_SUCCESS if initialization was successful or ARM_MATH_LENGTH_ERROR if
 * <code>blockSize</code> is not a multiple of <code>M</code>.
 *
 * <b>Description:</b>
 * \par
 * <code>pCoeffs</code> points to the array of filter coefficients stored in time reversed order:
 * <pre>
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
 * </pre>
 * \par
 * <code>pState</code> points to the array of state variables.
 * <code>pState</code> is of length <code>numTaps+blockSize-1</code> words where <code>blockSize</code> is the number of input samples passed to <code>arm_fir_decimate_q31()</code>.
 * <code>M</code> is the decimation factor.
 */

arm_status arm_fir_decimate_init_q31(
  arm_fir_decimate_instance_q31 * S,
  uint16_t numTaps,
  uint8_t M,
  q31_t * pCoeffs,
  q31_t * pState,
  uint32_t blockSize)
{
  arm_status status;

  /* The size of the input block must be a multiple of the decimation factor */
  if ((blockSize % M) != 0U)
  {
    /* Set status as ARM_MATH_LENGTH_ERROR */
    status = ARM_MATH_LENGTH_ERROR;
  }
  else
  {
    /* Assign filter taps */
    S->numTaps = numTaps;

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

    /* Clear the state buffer.  The size is always (blockSize + numTaps - 1) */
    memset(pState, 0, (numTaps + (blockSize - 1)) * sizeof(q31_t));

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

    /* Assign Decimation factor */
    S->M = M;

    status = ARM_MATH_SUCCESS;
  }

  return (status);

}

/**
 * @} end of FIR_decimate group
 */