/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_fir_fast_q31.c
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* Description: Processing function for the Q31 Fast FIR filter
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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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* @addtogroup FIR
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* @{
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*/
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/**
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* @param[in] *S points to an instance of the Q31 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 output data.
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* @param[in] blockSize number of 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.
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*
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* \par
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* Refer to the function <code>arm_fir_q31()</code> for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision. Both the slow and the fast versions use the same instance structure.
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* Use the function <code>arm_fir_init_q31()</code> to initialize the filter structure.
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*/
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IAR_ONLY_LOW_OPTIMIZATION_ENTER
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void arm_fir_fast_q31(
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const arm_fir_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, x1, x2, x3; /* Temporary variables to hold state */
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q31_t c0; /* Temporary variable to hold coefficient value */
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q31_t *px; /* Temporary pointer for state */
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q31_t *pb; /* Temporary pointer for coefficient buffer */
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q31_t acc0, acc1, acc2, acc3; /* 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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/* 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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/* Apply loop unrolling and 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 >> 2;
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/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
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** a second loop below computes the remaining 1 to 3 samples. */
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while (blkCnt > 0U)
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{
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/* Copy four 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 three 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 >> 2;
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i = tapCnt;
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while (i > 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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multAcc_32x32_keep32_R(acc0, x0, c0);
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/* acc1 += b[numTaps] * x[n-numTaps-1] */
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multAcc_32x32_keep32_R(acc1, x1, c0);
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/* acc2 += b[numTaps] * x[n-numTaps-2] */
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multAcc_32x32_keep32_R(acc2, x2, c0);
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/* acc3 += b[numTaps] * x[n-numTaps-3] */
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multAcc_32x32_keep32_R(acc3, 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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multAcc_32x32_keep32_R(acc0, x1, c0);
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multAcc_32x32_keep32_R(acc1, x2, c0);
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multAcc_32x32_keep32_R(acc2, x3, c0);
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multAcc_32x32_keep32_R(acc3, 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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multAcc_32x32_keep32_R(acc0, x2, c0);
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multAcc_32x32_keep32_R(acc1, x3, c0);
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multAcc_32x32_keep32_R(acc2, x0, c0);
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multAcc_32x32_keep32_R(acc3, 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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multAcc_32x32_keep32_R(acc0, x3, c0);
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multAcc_32x32_keep32_R(acc1, x0, c0);
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multAcc_32x32_keep32_R(acc2, x1, c0);
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multAcc_32x32_keep32_R(acc3, 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 the loop counter */
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i--;
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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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i = numTaps - (tapCnt * 4U);
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while (i > 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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multAcc_32x32_keep32_R(acc0, x0, c0);
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multAcc_32x32_keep32_R(acc1, x1, c0);
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multAcc_32x32_keep32_R(acc2, x2, c0);
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multAcc_32x32_keep32_R(acc3, 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 the loop counter */
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i--;
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}
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/* Advance the state pointer by 4 to process the next group of 4 samples */
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pState = pState + 4;
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/* The results in the 4 accumulators are in 2.30 format. Convert to 1.31
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** Then store the 4 outputs 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 the samples loop counter */
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blkCnt--;
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}
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/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
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** No loop unrolling is used. */
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blkCnt = blockSize % 4U;
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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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multAcc_32x32_keep32_R(acc0, (*px++), (*(pb++)));
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i--;
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} while (i > 0U);
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/* The result is in 2.30 format. Convert to 1.31
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** Then store the output in the destination buffer. */
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*pDst++ = (q31_t) (acc0 << 1);
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/* Advance state pointer by 1 for the next sample */
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pState = pState + 1;
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/* Decrement the samples 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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/* Calculate remaining number of copies */
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tapCnt = (numTaps - 1U);
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/* Copy the remaining q31_t 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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IAR_ONLY_LOW_OPTIMIZATION_EXIT
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/**
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* @} end of FIR group
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*/
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