391 lines
12 KiB
C
391 lines
12 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_fir_decimate_fast_q31.c
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* Description: Fast Q31 FIR Decimator
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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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@addtogroup FIR_decimate
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@{
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*/
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/**
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@brief Processing function for the Q31 FIR decimator (fast variant).
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@param[in] S points to an instance of the Q31 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 samples to process
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@return none
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@par Scaling and Overflow Behavior
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This function is optimized for speed at the expense of fixed-point precision and overflow protection.
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The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format.
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These intermediate results are added to a 2.30 accumulator.
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Finally, the accumulator is saturated and converted to a 1.31 result.
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The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result.
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In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2).
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@remark
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Refer to \ref arm_fir_decimate_q31() for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision.
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Both the slow and the fast versions use the same instance structure.
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Use function \ref arm_fir_decimate_init_q31() to initialize the filter structure.
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*/
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void arm_fir_decimate_fast_q31(
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const arm_fir_decimate_instance_q31 * S,
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const q31_t * pSrc,
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q31_t * pDst,
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uint32_t blockSize)
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{
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q31_t *pState = S->pState; /* State pointer */
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const q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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q31_t *pStateCur; /* Points to the current sample of the state */
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q31_t *px0; /* Temporary pointer for state buffer */
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const q31_t *pb; /* Temporary pointer for coefficient buffer */
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q31_t x0, c0; /* Temporary variables to hold state and coefficient values */
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q63_t acc0; /* Accumulator */
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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_LOOPUNROLL)
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q31_t *px1, *px2, *px3;
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q31_t x1, x2, x3;
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q63_t acc1, acc2, acc3;
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#endif
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/* S->pState buffer contains previous frame (numTaps - 1) samples */
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/* pStateCur points to the location where the new input data should be written */
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pStateCur = S->pState + (numTaps - 1U);
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 samples at a time */
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blkCnt = outBlockSize >> 2U;
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/* Samples loop unrolled by 4 */
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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 = S->M * 4;
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do
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{
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*pStateCur++ = *pSrc++;
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} while (--i);
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/* Set accumulators to zero */
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acc0 = 0;
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acc1 = 0;
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acc2 = 0;
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acc3 = 0;
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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: Compute 4 taps at a time */
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tapCnt = numTaps >> 2U;
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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 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
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acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
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acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
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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 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
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acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
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acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
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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 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
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acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
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acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
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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 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
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acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
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acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
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/* Decrement loop counter */
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tapCnt--;
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}
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/* Loop unrolling: Compute remaining 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 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
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acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
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acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
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/* Decrement 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 * 4;
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/* The result is in the accumulator, store in the destination buffer. */
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*pDst++ = (q31_t) (acc0 << 1);
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*pDst++ = (q31_t) (acc1 << 1);
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*pDst++ = (q31_t) (acc2 << 1);
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*pDst++ = (q31_t) (acc3 << 1);
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining samples */
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blkCnt = outBlockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of samples */
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blkCnt = outBlockSize;
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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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/* 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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*pStateCur++ = *pSrc++;
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} while (--i);
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/* Set accumulator to zero */
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acc0 = 0;
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/* Initialize state pointer */
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px0 = pState;
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/* Initialize coeff pointer */
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pb = pCoeffs;
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 taps at a time */
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tapCnt = numTaps >> 2U;
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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 = *px0++;
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/* Perform the multiply-accumulate */
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acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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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 = *px0++;
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/* Perform the multiply-accumulate */
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acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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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 = *px0++;
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/* Perform the multiply-accumulate */
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acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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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 = *px0++;
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/* Perform the multiply-accumulate */
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acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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/* Decrement loop counter */
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tapCnt--;
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}
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/* Loop unrolling: Compute remaining taps */
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tapCnt = numTaps % 0x4U;
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#else
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/* Initialize tapCnt with number of taps */
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tapCnt = numTaps;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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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 = *px0++;
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/* Perform the multiply-accumulate */
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acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
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/* Decrement 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++ = (q31_t) (acc0 << 1);
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/* Decrement 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 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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pStateCur = S->pState;
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 taps at a time */
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tapCnt = (numTaps - 1U) >> 2U;
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/* Copy data */
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while (tapCnt > 0U)
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{
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*pStateCur++ = *pState++;
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*pStateCur++ = *pState++;
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*pStateCur++ = *pState++;
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*pStateCur++ = *pState++;
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/* Decrement loop counter */
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tapCnt--;
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}
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/* Loop unrolling: Compute remaining taps */
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tapCnt = (numTaps - 1U) % 0x04U;
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#else
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/* Initialize tapCnt with number of taps */
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tapCnt = (numTaps - 1U);
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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/* Copy data */
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while (tapCnt > 0U)
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{
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*pStateCur++ = *pState++;
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/* Decrement loop counter */
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tapCnt--;
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}
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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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