/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_lms_q15.c
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* Description: Processing function for Q15 LMS filter
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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 LMS
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@{
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*/
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/**
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@brief Processing function for Q15 LMS filter.
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@param[in] S points to an instance of the Q15 LMS filter structure
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@param[in] pSrc points to the block of input data
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@param[in] pRef points to the block of reference data
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@param[out] pOut points to the block of output data
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@param[out] pErr points to the block of error 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 an internal 64-bit accumulator.
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Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result.
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The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 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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After all additions have been performed, the accumulator is truncated to 34.15 format by discarding low 15 bits.
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Lastly, the accumulator is saturated to yield a result in 1.15 format.
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@par
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In this filter, filter coefficients are updated for each sample and
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the updation of filter cofficients are saturted.
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*/
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void arm_lms_q15(
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const arm_lms_instance_q15 * S,
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const q15_t * pSrc,
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q15_t * pRef,
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q15_t * pOut,
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q15_t * pErr,
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uint32_t blockSize)
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{
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q15_t *pState = S->pState; /* State pointer */
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q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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q15_t *pStateCurnt; /* Points to the current sample of the state */
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q15_t *px, *pb; /* Temporary pointers for state and coefficient buffers */
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q15_t mu = S->mu; /* Adaptive factor */
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uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
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uint32_t tapCnt, blkCnt; /* Loop counters */
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q63_t acc; /* Accumulator */
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q15_t e = 0; /* Error of data sample */
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q15_t alpha; /* Intermediate constant for taps update */
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q31_t coef; /* Temporary variable for coefficient */
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q31_t acc_l, acc_h; /* Temporary input */
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int32_t lShift = (15 - (int32_t) S->postShift); /* Post shift */
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int32_t uShift = (32 - lShift);
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/* S->pState points to buffer 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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/* initialise loop count */
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blkCnt = blockSize;
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while (blkCnt > 0U)
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{
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/* Copy the new input sample into the state buffer */
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*pStateCurnt++ = *pSrc++;
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/* Initialize pState pointer */
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px = pState;
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/* Initialize coefficient pointer */
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pb = pCoeffs;
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/* Set the accumulator to zero */
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acc = 0;
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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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/* Perform the multiply-accumulate */
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/* acc += b[N] * x[n-N] + b[N-1] * x[n-N-1] */
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acc = __SMLALD(read_q15x2_ia (&px), read_q15x2_ia (&pb), acc);
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acc = __SMLALD(read_q15x2_ia (&px), read_q15x2_ia (&pb), acc);
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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 samples */
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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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/* Perform the multiply-accumulate */
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acc += (q63_t) (((q31_t) (*px++) * (*pb++)));
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/* Decrement the loop counter */
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tapCnt--;
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}
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/* Calc lower part of acc */
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acc_l = acc & 0xffffffff;
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/* Calc upper part of acc */
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acc_h = (acc >> 32) & 0xffffffff;
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/* Apply shift for lower part of acc and upper part of acc */
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acc = (uint32_t) acc_l >> lShift | acc_h << uShift;
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/* Converting the result to 1.15 format and saturate the output */
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acc = __SSAT(acc, 16U);
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/* Store the result from accumulator into the destination buffer. */
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*pOut++ = (q15_t) acc;
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/* Compute and store error */
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e = *pRef++ - (q15_t) acc;
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*pErr++ = (q15_t) e;
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/* Compute alpha i.e. intermediate constant for taps update */
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alpha = (q15_t) (((q31_t) e * (mu)) >> 15);
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/* Initialize pState pointer */
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/* Advance state pointer by 1 for the next sample */
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px = pState++;
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/* Initialize coefficient 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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/* Update filter coefficients */
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while (tapCnt > 0U)
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{
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coef = (q31_t) *pb + (((q31_t) alpha * (*px++)) >> 15);
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*pb++ = (q15_t) __SSAT((coef), 16);
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coef = (q31_t) *pb + (((q31_t) alpha * (*px++)) >> 15);
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*pb++ = (q15_t) __SSAT((coef), 16);
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coef = (q31_t) *pb + (((q31_t) alpha * (*px++)) >> 15);
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*pb++ = (q15_t) __SSAT((coef), 16);
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coef = (q31_t) *pb + (((q31_t) alpha * (*px++)) >> 15);
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*pb++ = (q15_t) __SSAT((coef), 16);
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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 samples */
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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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/* Perform the multiply-accumulate */
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coef = (q31_t) *pb + (((q31_t) alpha * (*px++)) >> 15);
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*pb++ = (q15_t) __SSAT((coef), 16);
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/* Decrement loop counter */
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tapCnt--;
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}
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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 pState buffer */
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pStateCurnt = S->pState;
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/* copy data */
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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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while (tapCnt > 0U)
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{
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write_q15x2_ia (&pStateCurnt, read_q15x2_ia (&pState));
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write_q15x2_ia (&pStateCurnt, read_q15x2_ia (&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) % 0x4U;
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#else
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/* Initialize tapCnt with number of samples */
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tapCnt = (numTaps - 1U);
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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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*pStateCurnt++ = *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 LMS group
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*/
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