/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_fir_sparse_f32.c
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* Description: Floating-point sparse FIR filter processing function
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*
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* $Date: 18. March 2019
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* $Revision: V1.6.0
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the License); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an AS IS BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "arm_math.h"
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/**
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@ingroup groupFilters
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*/
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/**
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@defgroup FIR_Sparse Finite Impulse Response (FIR) Sparse Filters
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This group of functions implements sparse FIR filters.
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Sparse FIR filters are equivalent to standard FIR filters except that most of the coefficients are equal to zero.
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Sparse filters are used for simulating reflections in communications and audio applications.
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There are separate functions for Q7, Q15, Q31, and floating-point data types.
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The functions operate on blocks of input and output data and each call to the function processes
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<code>blockSize</code> samples through the filter. <code>pSrc</code> and
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<code>pDst</code> points to input and output arrays respectively containing <code>blockSize</code> values.
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@par Algorithm
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The sparse filter instant structure contains an array of tap indices <code>pTapDelay</code> which specifies the locations of the non-zero coefficients.
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This is in addition to the coefficient array <code>b</code>.
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The implementation essentially skips the multiplications by zero and leads to an efficient realization.
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<pre>
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y[n] = b[0] * x[n-pTapDelay[0]] + b[1] * x[n-pTapDelay[1]] + b[2] * x[n-pTapDelay[2]] + ...+ b[numTaps-1] * x[n-pTapDelay[numTaps-1]]
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</pre>
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@par
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\image html FIRSparse.gif "Sparse FIR filter. b[n] represents the filter coefficients"
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@par
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<code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>;
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<code>pTapDelay</code> points to an array of nonzero indices and is also of size <code>numTaps</code>;
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<code>pState</code> points to a state array of size <code>maxDelay + blockSize</code>, where
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<code>maxDelay</code> is the largest offset value that is ever used in the <code>pTapDelay</code> array.
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Some of the processing functions also require temporary working buffers.
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@par Instance Structure
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The coefficients and state variables for a filter are stored together in an instance data structure.
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A separate instance structure must be defined for each filter.
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Coefficient and offset arrays may be shared among several instances while state variable arrays cannot be shared.
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There are separate instance structure declarations for each of the 4 supported data types.
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@par Initialization Functions
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There is also an associated initialization function for each data type.
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The initialization function performs the following operations:
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- Sets the values of the internal structure fields.
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- Zeros out the values in the state buffer.
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To do this manually without calling the init function, assign the follow subfields of the instance structure:
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numTaps, pCoeffs, pTapDelay, maxDelay, stateIndex, pState. Also set all of the values in pState to zero.
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@par
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Use of the initialization function is optional.
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However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
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To place an instance structure into a const data section, the instance structure must be manually initialized.
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Set the values in the state buffer to zeros before static initialization.
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The code below statically initializes each of the 4 different data type filter instance structures
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<pre>
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arm_fir_sparse_instance_f32 S = {numTaps, 0, pState, pCoeffs, maxDelay, pTapDelay};
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arm_fir_sparse_instance_q31 S = {numTaps, 0, pState, pCoeffs, maxDelay, pTapDelay};
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arm_fir_sparse_instance_q15 S = {numTaps, 0, pState, pCoeffs, maxDelay, pTapDelay};
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arm_fir_sparse_instance_q7 S = {numTaps, 0, pState, pCoeffs, maxDelay, pTapDelay};
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</pre>
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@par Fixed-Point Behavior
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Care must be taken when using the fixed-point versions of the sparse FIR filter functions.
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In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
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Refer to the function specific documentation below for usage guidelines.
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*/
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/**
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@addtogroup FIR_Sparse
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@{
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*/
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/**
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@brief Processing function for the floating-point sparse FIR filter.
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@param[in] S points to an instance of the floating-point sparse FIR structure
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@param[in] pSrc points to the block of input data
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@param[out] pDst points to the block of output data
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@param[in] pScratchIn points to a temporary buffer of size blockSize
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@param[in] blockSize number of input samples to process
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@return none
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*/
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void arm_fir_sparse_f32(
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arm_fir_sparse_instance_f32 * S,
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const float32_t * pSrc,
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float32_t * pDst,
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float32_t * pScratchIn,
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uint32_t blockSize)
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{
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float32_t *pState = S->pState; /* State pointer */
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const float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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float32_t *px; /* Scratch buffer pointer */
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float32_t *py = pState; /* Temporary pointers for state buffer */
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float32_t *pb = pScratchIn; /* Temporary pointers for scratch buffer */
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float32_t *pOut; /* Destination pointer */
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int32_t *pTapDelay = S->pTapDelay; /* Pointer to the array containing offset of the non-zero tap values. */
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uint32_t delaySize = S->maxDelay + blockSize; /* state length */
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uint16_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
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int32_t readIndex; /* Read index of the state buffer */
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uint32_t tapCnt, blkCnt; /* loop counters */
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float32_t coeff = *pCoeffs++; /* Read the first coefficient value */
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/* BlockSize of Input samples are copied into the state buffer */
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/* StateIndex points to the starting position to write in the state buffer */
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arm_circularWrite_f32((int32_t *) py, delaySize, &S->stateIndex, 1, (int32_t *) pSrc, 1, blockSize);
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/* Read Index, from where the state buffer should be read, is calculated. */
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readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;
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/* Wraparound of readIndex */
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if (readIndex < 0)
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{
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readIndex += (int32_t) delaySize;
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}
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/* Working pointer for state buffer is updated */
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py = pState;
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/* blockSize samples are read from the state buffer */
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arm_circularRead_f32((int32_t *) py, delaySize, &readIndex, 1,
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(int32_t *) pb, (int32_t *) pb, blockSize, 1, blockSize);
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/* Working pointer for the scratch buffer of state values */
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px = pb;
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/* Working pointer for scratch buffer of output values */
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pOut = pDst;
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 outputs at a time. */
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blkCnt = blockSize >> 2U;
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while (blkCnt > 0U)
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{
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/* Perform Multiplications and store in destination buffer */
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*pOut++ = *px++ * coeff;
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*pOut++ = *px++ * coeff;
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*pOut++ = *px++ * coeff;
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*pOut++ = *px++ * coeff;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining outputs */
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blkCnt = blockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of samples */
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blkCnt = blockSize;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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while (blkCnt > 0U)
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{
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/* Perform Multiplication and store in destination buffer */
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*pOut++ = *px++ * coeff;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Load the coefficient value and
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* increment the coefficient buffer for the next set of state values */
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coeff = *pCoeffs++;
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/* Read Index, from where the state buffer should be read, is calculated. */
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readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;
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/* Wraparound of readIndex */
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if (readIndex < 0)
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{
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readIndex += (int32_t) delaySize;
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}
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/* Loop over the number of taps. */
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tapCnt = (uint32_t) numTaps - 2U;
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while (tapCnt > 0U)
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{
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/* Working pointer for state buffer is updated */
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py = pState;
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/* blockSize samples are read from the state buffer */
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arm_circularRead_f32((int32_t *) py, delaySize, &readIndex, 1,
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(int32_t *) pb, (int32_t *) pb, blockSize, 1, blockSize);
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/* Working pointer for the scratch buffer of state values */
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px = pb;
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/* Working pointer for scratch buffer of output values */
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pOut = pDst;
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 outputs at a time. */
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blkCnt = blockSize >> 2U;
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while (blkCnt > 0U)
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{
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/* Perform Multiply-Accumulate */
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*pOut++ += *px++ * coeff;
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*pOut++ += *px++ * coeff;
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*pOut++ += *px++ * coeff;
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*pOut++ += *px++ * coeff;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining outputs */
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blkCnt = blockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of samples */
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blkCnt = blockSize;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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while (blkCnt > 0U)
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{
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/* Perform Multiply-Accumulate */
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*pOut++ += *px++ * coeff;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Load the coefficient value and
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* increment the coefficient buffer for the next set of state values */
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coeff = *pCoeffs++;
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/* Read Index, from where the state buffer should be read, is calculated. */
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readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;
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/* Wraparound of readIndex */
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if (readIndex < 0)
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{
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readIndex += (int32_t) delaySize;
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}
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/* Decrement tap loop counter */
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tapCnt--;
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}
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/* Compute last tap without the final read of pTapDelay */
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/* Working pointer for state buffer is updated */
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py = pState;
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/* blockSize samples are read from the state buffer */
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arm_circularRead_f32((int32_t *) py, delaySize, &readIndex, 1,
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(int32_t *) pb, (int32_t *) pb, blockSize, 1, blockSize);
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/* Working pointer for the scratch buffer of state values */
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px = pb;
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/* Working pointer for scratch buffer of output values */
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pOut = pDst;
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 outputs at a time. */
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blkCnt = blockSize >> 2U;
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while (blkCnt > 0U)
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{
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/* Perform Multiply-Accumulate */
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*pOut++ += *px++ * coeff;
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*pOut++ += *px++ * coeff;
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*pOut++ += *px++ * coeff;
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*pOut++ += *px++ * coeff;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining outputs */
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blkCnt = blockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of samples */
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blkCnt = blockSize;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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while (blkCnt > 0U)
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{
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/* Perform Multiply-Accumulate */
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*pOut++ += *px++ * coeff;
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/* Decrement loop counter */
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blkCnt--;
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}
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}
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/**
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@} end of FIR_Sparse group
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*/
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