/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_fir_decimate_f32.c
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* Description: FIR decimation for floating-point sequences
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*
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* $Date: 27. January 2017
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* $Revision: V.1.5.1
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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) 2010-2017 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_decimate Finite Impulse Response (FIR) Decimator
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*
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* These functions combine an FIR filter together with a decimator.
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* They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.
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* Conceptually, the functions are equivalent to the block diagram below:
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* \image html FIRDecimator.gif "Components included in the FIR Decimator functions"
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* When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized
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* cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.
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* The user of the function is responsible for providing the filter coefficients.
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*
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* The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.
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* Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the
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* samples output by the decimator are computed.
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* The functions operate on blocks of input and output data.
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* <code>pSrc</code> points to an array of <code>blockSize</code> input values and
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* <code>pDst</code> points to an array of <code>blockSize/M</code> output values.
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* In order to have an integer number of output samples <code>blockSize</code>
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* must always be a multiple of the decimation factor <code>M</code>.
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*
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* The library provides separate functions for Q15, Q31 and floating-point data types.
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*
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* \par Algorithm:
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* The FIR portion of the algorithm uses the standard form filter:
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* <pre>
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* y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]
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* </pre>
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* where, <code>b[n]</code> are the filter coefficients.
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* \par
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* The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.
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* Coefficients are stored in time reversed order.
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* \par
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* <pre>
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* {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}
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* </pre>
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* \par
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* <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.
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* Samples in the state buffer are stored in the order:
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* \par
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* <pre>
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* {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}
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* </pre>
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* The state variables are updated after each block of data is processed, the coefficients are untouched.
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*
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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 arrays may be shared among several instances while state variable array should be allocated separately.
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* There are separate instance structure declarations for each of the 3 supported data types.
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*
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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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* - Checks to make sure that the size of the input is a multiple of the decimation factor.
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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, M (decimation factor), pState. Also set all of the values in pState to zero.
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*
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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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* The code below statically initializes each of the 3 different data type filter instance structures
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* <pre>
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*arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};
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*arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};
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*arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};
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* </pre>
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* where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;
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* <code>pCoeffs</code> is the address of the coefficient buffer;
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* <code>pState</code> is the address of the state buffer.
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* Be sure to set the values in the state buffer to zeros when doing static initialization.
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*
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* \par Fixed-Point Behavior
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* Care must be taken when using the fixed-point versions of the FIR decimate 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_decimate
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* @{
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*/
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/**
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* @brief Processing function for the floating-point FIR decimator.
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* @param[in] *S points to an instance of the floating-point FIR decimator 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] blockSize number of input samples to process per call.
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* @return none.
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*/
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void arm_fir_decimate_f32(
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const arm_fir_decimate_instance_f32 * S,
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float32_t * pSrc,
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float32_t * pDst,
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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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float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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float32_t *pStateCurnt; /* Points to the current sample of the state */
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float32_t *px, *pb; /* Temporary pointers for state and coefficient buffers */
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float32_t sum0; /* Accumulator */
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float32_t x0, c0; /* Temporary variables to hold state and coefficient values */
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uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
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uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
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#if defined (ARM_MATH_DSP)
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uint32_t blkCntN4;
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float32_t *px0, *px1, *px2, *px3;
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float32_t acc0, acc1, acc2, acc3;
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float32_t x1, x2, x3;
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/* Run the below code for Cortex-M4 and Cortex-M3 */
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/* S->pState buffer contains previous frame (numTaps - 1) samples */
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/* pStateCurnt points to the location where the new input data should be written */
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pStateCurnt = S->pState + (numTaps - 1U);
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/* Total number of output samples to be computed */
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blkCnt = outBlockSize / 4;
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blkCntN4 = outBlockSize - (4 * blkCnt);
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while (blkCnt > 0U)
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{
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/* Copy 4 * decimation factor number of new input samples into the state buffer */
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i = 4 * S->M;
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do
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{
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*pStateCurnt++ = *pSrc++;
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} while (--i);
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/* Set accumulators to zero */
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acc0 = 0.0f;
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acc1 = 0.0f;
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acc2 = 0.0f;
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acc3 = 0.0f;
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/* Initialize state pointer for all the samples */
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px0 = pState;
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px1 = pState + S->M;
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px2 = pState + 2 * S->M;
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px3 = pState + 3 * S->M;
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/* Initialize coeff pointer */
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pb = pCoeffs;
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/* Loop unrolling. Process 4 taps at a time. */
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tapCnt = numTaps >> 2;
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/* Loop over the number of taps. Unroll by a factor of 4.
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** Repeat until we've computed numTaps-4 coefficients. */
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while (tapCnt > 0U)
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{
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/* Read the b[numTaps-1] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-1] sample for acc0 */
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x0 = *(px0++);
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/* Read x[n-numTaps-1] sample for acc1 */
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x1 = *(px1++);
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/* Read x[n-numTaps-1] sample for acc2 */
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x2 = *(px2++);
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/* Read x[n-numTaps-1] sample for acc3 */
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x3 = *(px3++);
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/* Perform the multiply-accumulate */
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acc0 += x0 * c0;
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acc1 += x1 * c0;
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acc2 += x2 * c0;
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acc3 += x3 * c0;
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/* Read the b[numTaps-2] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */
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x0 = *(px0++);
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x1 = *(px1++);
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x2 = *(px2++);
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x3 = *(px3++);
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/* Perform the multiply-accumulate */
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acc0 += x0 * c0;
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acc1 += x1 * c0;
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acc2 += x2 * c0;
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acc3 += x3 * c0;
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/* Read the b[numTaps-3] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */
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x0 = *(px0++);
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x1 = *(px1++);
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x2 = *(px2++);
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x3 = *(px3++);
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/* Perform the multiply-accumulate */
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acc0 += x0 * c0;
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acc1 += x1 * c0;
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acc2 += x2 * c0;
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acc3 += x3 * c0;
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/* Read the b[numTaps-4] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */
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x0 = *(px0++);
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x1 = *(px1++);
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x2 = *(px2++);
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x3 = *(px3++);
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/* Perform the multiply-accumulate */
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acc0 += x0 * c0;
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acc1 += x1 * c0;
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acc2 += x2 * c0;
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acc3 += x3 * c0;
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* If the filter length is not a multiple of 4, compute the remaining filter taps */
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tapCnt = numTaps % 0x4U;
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while (tapCnt > 0U)
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{
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/* Read coefficients */
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c0 = *(pb++);
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/* Fetch state variables for acc0, acc1, acc2, acc3 */
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x0 = *(px0++);
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x1 = *(px1++);
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x2 = *(px2++);
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x3 = *(px3++);
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/* Perform the multiply-accumulate */
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acc0 += x0 * c0;
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acc1 += x1 * c0;
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acc2 += x2 * c0;
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acc3 += x3 * c0;
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* Advance the state pointer by the decimation factor
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* to process the next group of decimation factor number samples */
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pState = pState + 4 * S->M;
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/* The result is in the accumulator, store in the destination buffer. */
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*pDst++ = acc0;
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*pDst++ = acc1;
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*pDst++ = acc2;
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*pDst++ = acc3;
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/* Decrement the loop counter */
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blkCnt--;
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}
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while (blkCntN4 > 0U)
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{
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/* Copy decimation factor number of new input samples into the state buffer */
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i = S->M;
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do
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{
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*pStateCurnt++ = *pSrc++;
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} while (--i);
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/* Set accumulator to zero */
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sum0 = 0.0f;
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/* Initialize state pointer */
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px = pState;
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/* Initialize coeff pointer */
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pb = pCoeffs;
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/* Loop unrolling. Process 4 taps at a time. */
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tapCnt = numTaps >> 2;
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/* Loop over the number of taps. Unroll by a factor of 4.
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** Repeat until we've computed numTaps-4 coefficients. */
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while (tapCnt > 0U)
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{
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/* Read the b[numTaps-1] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-1] sample */
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x0 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 += x0 * c0;
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/* Read the b[numTaps-2] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-2] sample */
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x0 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 += x0 * c0;
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/* Read the b[numTaps-3] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-3] sample */
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x0 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 += x0 * c0;
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/* Read the b[numTaps-4] coefficient */
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c0 = *(pb++);
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/* Read x[n-numTaps-4] sample */
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x0 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 += x0 * c0;
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* If the filter length is not a multiple of 4, compute the remaining filter taps */
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tapCnt = numTaps % 0x4U;
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while (tapCnt > 0U)
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{
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/* Read coefficients */
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c0 = *(pb++);
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/* Fetch 1 state variable */
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x0 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 += x0 * c0;
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* Advance the state pointer by the decimation factor
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* to process the next group of decimation factor number samples */
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pState = pState + S->M;
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/* The result is in the accumulator, store in the destination buffer. */
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*pDst++ = sum0;
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/* Decrement the loop counter */
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blkCntN4--;
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}
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/* Processing is complete.
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** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
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** This prepares the state buffer for the next function call. */
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/* Points to the start of the state buffer */
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pStateCurnt = S->pState;
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i = (numTaps - 1U) >> 2;
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/* copy data */
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while (i > 0U)
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{
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*pStateCurnt++ = *pState++;
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*pStateCurnt++ = *pState++;
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*pStateCurnt++ = *pState++;
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*pStateCurnt++ = *pState++;
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/* Decrement the loop counter */
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i--;
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}
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i = (numTaps - 1U) % 0x04U;
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/* copy data */
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while (i > 0U)
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{
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*pStateCurnt++ = *pState++;
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/* Decrement the loop counter */
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i--;
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}
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#else
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/* Run the below code for Cortex-M0 */
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/* S->pState buffer contains previous frame (numTaps - 1) samples */
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/* pStateCurnt points to the location where the new input data should be written */
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pStateCurnt = S->pState + (numTaps - 1U);
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/* Total number of output samples to be computed */
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blkCnt = outBlockSize;
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while (blkCnt > 0U)
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{
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/* Copy decimation factor number of new input samples into the state buffer */
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i = S->M;
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do
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{
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*pStateCurnt++ = *pSrc++;
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} while (--i);
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/* Set accumulator to zero */
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sum0 = 0.0f;
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/* Initialize state pointer */
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px = pState;
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/* Initialize coeff pointer */
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pb = pCoeffs;
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tapCnt = numTaps;
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while (tapCnt > 0U)
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{
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/* Read coefficients */
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c0 = *pb++;
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/* Fetch 1 state variable */
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x0 = *px++;
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/* Perform the multiply-accumulate */
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sum0 += x0 * c0;
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* Advance the state pointer by the decimation factor
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* to process the next group of decimation factor number samples */
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pState = pState + S->M;
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/* The result is in the accumulator, store in the destination buffer. */
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*pDst++ = sum0;
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/* Decrement the loop counter */
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blkCnt--;
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}
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/* Processing is complete.
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** Now copy the last numTaps - 1 samples to the start of the state buffer.
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** This prepares the state buffer for the next function call. */
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/* Points to the start of the state buffer */
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pStateCurnt = S->pState;
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/* Copy numTaps number of values */
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i = (numTaps - 1U);
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/* copy data */
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while (i > 0U)
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{
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*pStateCurnt++ = *pState++;
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/* Decrement the loop counter */
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i--;
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}
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#endif /* #if defined (ARM_MATH_DSP) */
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}
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/**
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* @} end of FIR_decimate group
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*/
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