324 lines
9.3 KiB
C
324 lines
9.3 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_fir_q7.c
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* Description: Q7 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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@addtogroup FIR
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@{
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*/
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/**
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@brief Processing function for Q7 FIR filter.
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@param[in] S points to an instance of the Q7 FIR filter 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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The function is implemented using a 32-bit internal accumulator.
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Both coefficients and state variables are represented in 1.7 format and multiplications yield a 2.14 result.
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The 2.14 intermediate results are accumulated in a 32-bit accumulator in 18.14 format.
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There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved.
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The accumulator is converted to 18.7 format by discarding the low 7 bits.
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Finally, the result is truncated to 1.7 format.
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*/
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void arm_fir_q7(
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const arm_fir_instance_q7 * S,
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const q7_t * pSrc,
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q7_t * pDst,
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uint32_t blockSize)
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{
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q7_t *pState = S->pState; /* State pointer */
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const q7_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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q7_t *pStateCurnt; /* Points to the current sample of the state */
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q7_t *px; /* Temporary pointer for state buffer */
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const q7_t *pb; /* Temporary pointer for coefficient buffer */
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q31_t acc0; /* Accumulators */
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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; /* Loop counters */
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#if defined (ARM_MATH_LOOPUNROLL)
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q31_t acc1, acc2, acc3; /* Accumulators */
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q7_t x0, x1, x2, x3, c0; /* Temporary variables to hold state */
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#endif
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/* S->pState points to state array which 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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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 output values simultaneously.
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* The variables acc0 ... acc3 hold output values that are being computed:
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*
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* acc0 = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]
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* acc1 = b[numTaps-1] * x[n-numTaps] + b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]
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* acc2 = b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] + b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]
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* acc3 = b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps] +...+ b[0] * x[3]
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*/
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blkCnt = blockSize >> 2U;
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while (blkCnt > 0U)
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{
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/* Copy 4 new input samples into the state buffer. */
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*pStateCurnt++ = *pSrc++;
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*pStateCurnt++ = *pSrc++;
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*pStateCurnt++ = *pSrc++;
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*pStateCurnt++ = *pSrc++;
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/* Set all 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 */
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px = pState;
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/* Initialize coefficient pointer */
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pb = pCoeffs;
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/* Read the first 3 samples from the state buffer:
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* x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
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x0 = *px++;
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x1 = *px++;
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x2 = *px++;
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/* Loop unrolling. Process 4 taps at a time. */
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tapCnt = numTaps >> 2U;
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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] coefficient */
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c0 = *pb;
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/* Read x[n-numTaps-3] sample */
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x3 = *px;
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/* acc0 += b[numTaps] * x[n-numTaps] */
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acc0 += ((q15_t) x0 * c0);
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/* acc1 += b[numTaps] * x[n-numTaps-1] */
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acc1 += ((q15_t) x1 * c0);
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/* acc2 += b[numTaps] * x[n-numTaps-2] */
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acc2 += ((q15_t) x2 * c0);
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/* acc3 += b[numTaps] * x[n-numTaps-3] */
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acc3 += ((q15_t) x3 * c0);
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/* Read the b[numTaps-1] coefficient */
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c0 = *(pb + 1U);
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/* Read x[n-numTaps-4] sample */
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x0 = *(px + 1U);
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/* Perform the multiply-accumulates */
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acc0 += ((q15_t) x1 * c0);
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acc1 += ((q15_t) x2 * c0);
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acc2 += ((q15_t) x3 * c0);
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acc3 += ((q15_t) x0 * c0);
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/* Read the b[numTaps-2] coefficient */
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c0 = *(pb + 2U);
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/* Read x[n-numTaps-5] sample */
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x1 = *(px + 2U);
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/* Perform the multiply-accumulates */
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acc0 += ((q15_t) x2 * c0);
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acc1 += ((q15_t) x3 * c0);
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acc2 += ((q15_t) x0 * c0);
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acc3 += ((q15_t) x1 * c0);
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/* Read the b[numTaps-3] coefficients */
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c0 = *(pb + 3U);
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/* Read x[n-numTaps-6] sample */
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x2 = *(px + 3U);
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/* Perform the multiply-accumulates */
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acc0 += ((q15_t) x3 * c0);
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acc1 += ((q15_t) x0 * c0);
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acc2 += ((q15_t) x1 * c0);
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acc3 += ((q15_t) x2 * c0);
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/* update coefficient pointer */
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pb += 4U;
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px += 4U;
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/* Decrement 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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x3 = *(px++);
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/* Perform the multiply-accumulates */
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acc0 += ((q15_t) x0 * c0);
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acc1 += ((q15_t) x1 * c0);
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acc2 += ((q15_t) x2 * c0);
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acc3 += ((q15_t) x3 * c0);
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/* Reuse the present sample states for next sample */
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x0 = x1;
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x1 = x2;
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x2 = x3;
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/* Decrement loop counter */
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tapCnt--;
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}
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/* The results in the 4 accumulators are in 2.62 format. Convert to 1.31
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Then store the 4 outputs in the destination buffer. */
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acc0 = __SSAT((acc0 >> 7U), 8);
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*pDst++ = acc0;
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acc1 = __SSAT((acc1 >> 7U), 8);
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*pDst++ = acc1;
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acc2 = __SSAT((acc2 >> 7U), 8);
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*pDst++ = acc2;
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acc3 = __SSAT((acc3 >> 7U), 8);
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*pDst++ = acc3;
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/* Advance the state pointer by 4 to process the next group of 4 samples */
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pState = pState + 4U;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining output samples */
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blkCnt = blockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of taps */
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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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/* Copy one sample at a time into state buffer */
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*pStateCurnt++ = *pSrc++;
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/* Set the accumulator to zero */
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acc0 = 0;
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/* Initialize state pointer */
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px = pState;
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/* Initialize Coefficient pointer */
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pb = pCoeffs;
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i = numTaps;
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/* Perform the multiply-accumulates */
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do
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{
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acc0 += (q15_t) * (px++) * (*(pb++));
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i--;
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} while (i > 0U);
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/* The result is in 2.14 format. Convert to 1.7
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Then store the output in the destination buffer. */
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*pDst++ = __SSAT((acc0 >> 7U), 8);
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/* Advance state pointer by 1 for the next sample */
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pState = pState + 1U;
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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 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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#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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*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 loop counter */
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tapCnt--;
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}
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/* Calculate remaining number of copies */
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tapCnt = (numTaps - 1U) % 0x4U;
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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 remaining data */
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while (tapCnt > 0U)
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{
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*pStateCurnt++ = *pState++;
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/* Decrement the 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 group
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*/
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