352 lines
11 KiB
C
352 lines
11 KiB
C
/* ----------------------------------------------------------------------
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* Copyright (C) 2010-2013 ARM Limited. All rights reserved.
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*
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* $Date: 17. January 2013
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* $Revision: V1.4.1
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*
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* Project: CMSIS DSP Library
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* Title: arm_fir_decimate_fast_q31.c
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*
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* Description: Fast Q31 FIR Decimator.
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*
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* Target Processor: Cortex-M4/Cortex-M3
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* - Neither the name of ARM LIMITED nor the names of its contributors
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* may be used to endorse or promote products derived from this
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* software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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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) for Cortex-M3 and Cortex-M4.
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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 input samples to process per call.
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* @return none
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*
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* <b>Scaling and Overflow Behavior:</b>
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*
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* \par
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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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*
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* \par
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* Refer to the function <code>arm_fir_decimate_q31()</code> 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 the function <code>arm_fir_decimate_init_q31()</code> to initialize the filter structure.
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*/
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void arm_fir_decimate_fast_q31(
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arm_fir_decimate_instance_q31 * S,
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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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q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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q31_t *pStateCurnt; /* Points to the current sample of the state */
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q31_t x0, c0; /* Temporary variables to hold state and coefficient values */
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q31_t *px; /* Temporary pointers for state buffer */
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q31_t *pb; /* Temporary pointers for coefficient buffer */
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q31_t sum0; /* Accumulator */
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uint32_t numTaps = S->numTaps; /* Number of taps */
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uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
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uint32_t blkCntN2;
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q31_t x1;
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q31_t acc0, acc1;
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q31_t *px0, *px1;
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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 / 2;
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blkCntN2 = outBlockSize - (2 * blkCnt);
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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 = 2 * 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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acc0 = 0;
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acc1 = 0;
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/* Initialize state pointer */
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px0 = pState;
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px1 = pState + 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] for sample 0 sample 1 */
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x0 = *(px0);
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x1 = *(px1);
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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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/* Read the b[numTaps-2] coefficient */
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c0 = *(pb + 1u);
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/* Read x[n-numTaps-2] for sample 0 sample 1 */
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x0 = *(px0 + 1u);
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x1 = *(px1 + 1u);
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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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/* Read the b[numTaps-3] coefficient */
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c0 = *(pb + 2u);
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/* Read x[n-numTaps-3] for sample 0 sample 1 */
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x0 = *(px0 + 2u);
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x1 = *(px1 + 2u);
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pb += 4u;
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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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/* Read the b[numTaps-4] coefficient */
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c0 = *(pb - 1u);
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/* Read x[n-numTaps-4] for sample 0 sample 1 */
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x0 = *(px0 + 3u);
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x1 = *(px1 + 3u);
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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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/* update state pointers */
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px0 += 4u;
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px1 += 4u;
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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 = *(px0++);
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x1 = *(px1++);
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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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/* 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 * 2;
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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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/* Decrement the loop counter */
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blkCnt--;
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}
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while(blkCntN2 > 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;
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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 = (q31_t) ((((q63_t) sum0 << 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 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 = (q31_t) ((((q63_t) sum0 << 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 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 = (q31_t) ((((q63_t) sum0 << 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 = *(px++);
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/* Perform the multiply-accumulate */
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sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
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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 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
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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++ = (q31_t) (sum0 << 1);
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/* Decrement the loop counter */
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blkCntN2--;
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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) >> 2u;
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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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}
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/**
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* @} end of FIR_decimate group
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*/
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