/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_fir_q31.c
* Description: Q31 FIR filter processing function
*
* $Date: 27. January 2017
* $Revision: V.1.5.1
*
* Target Processor: Cortex-M cores
* -------------------------------------------------------------------- */
/*
* Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the License); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an AS IS BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "arm_math.h"
/**
* @ingroup groupFilters
*/
/**
* @addtogroup FIR
* @{
*/
/**
* @param[in] *S points to an instance of the Q31 FIR filter structure.
* @param[in] *pSrc points to the block of input data.
* @param[out] *pDst points to the block of output data.
* @param[in] blockSize number of samples to process per call.
* @return none.
*
* @details
* Scaling and Overflow Behavior:
* \par
* The function is implemented using an internal 64-bit accumulator.
* The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
* Thus, if the accumulator result overflows it wraps around rather than clip.
* In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.
* After all multiply-accumulates are performed, the 2.62 accumulator is right shifted by 31 bits and saturated to 1.31 format to yield the final result.
*
* \par
* Refer to the function arm_fir_fast_q31() for a faster but less precise implementation of this filter for Cortex-M3 and Cortex-M4.
*/
void arm_fir_q31(
const arm_fir_instance_q31 * S,
q31_t * pSrc,
q31_t * pDst,
uint32_t blockSize)
{
q31_t *pState = S->pState; /* State pointer */
q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
q31_t *pStateCurnt; /* Points to the current sample of the state */
#if defined (ARM_MATH_DSP)
/* Run the below code for Cortex-M4 and Cortex-M3 */
q31_t x0, x1, x2; /* Temporary variables to hold state */
q31_t c0; /* Temporary variable to hold coefficient value */
q31_t *px; /* Temporary pointer for state */
q31_t *pb; /* Temporary pointer for coefficient buffer */
q63_t acc0, acc1, acc2; /* Accumulators */
uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */
uint32_t i, tapCnt, blkCnt, tapCntN3; /* Loop counters */
/* S->pState points to state array which contains previous frame (numTaps - 1) samples */
/* pStateCurnt points to the location where the new input data should be written */
pStateCurnt = &(S->pState[(numTaps - 1U)]);
/* Apply loop unrolling and compute 4 output values simultaneously.
* The variables acc0 ... acc3 hold output values that are being computed:
*
* 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]
* 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]
* 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]
* 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]
*/
blkCnt = blockSize / 3;
blockSize = blockSize - (3 * blkCnt);
tapCnt = numTaps / 3;
tapCntN3 = numTaps - (3 * tapCnt);
/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
** a second loop below computes the remaining 1 to 3 samples. */
while (blkCnt > 0U)
{
/* Copy three new input samples into the state buffer */
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
*pStateCurnt++ = *pSrc++;
/* Set all accumulators to zero */
acc0 = 0;
acc1 = 0;
acc2 = 0;
/* Initialize state pointer */
px = pState;
/* Initialize coefficient pointer */
pb = pCoeffs;
/* Read the first two samples from the state buffer:
* x[n-numTaps], x[n-numTaps-1] */
x0 = *(px++);
x1 = *(px++);
/* Loop unrolling. Process 3 taps at a time. */
i = tapCnt;
while (i > 0U)
{
/* Read the b[numTaps] coefficient */
c0 = *pb;
/* Read x[n-numTaps-2] sample */
x2 = *(px++);
/* Perform the multiply-accumulates */
acc0 += ((q63_t) x0 * c0);
acc1 += ((q63_t) x1 * c0);
acc2 += ((q63_t) x2 * c0);
/* Read the coefficient and state */
c0 = *(pb + 1U);
x0 = *(px++);
/* Perform the multiply-accumulates */
acc0 += ((q63_t) x1 * c0);
acc1 += ((q63_t) x2 * c0);
acc2 += ((q63_t) x0 * c0);
/* Read the coefficient and state */
c0 = *(pb + 2U);
x1 = *(px++);
/* update coefficient pointer */
pb += 3U;
/* Perform the multiply-accumulates */
acc0 += ((q63_t) x2 * c0);
acc1 += ((q63_t) x0 * c0);
acc2 += ((q63_t) x1 * c0);
/* Decrement the loop counter */
i--;
}
/* If the filter length is not a multiple of 3, compute the remaining filter taps */
i = tapCntN3;
while (i > 0U)
{
/* Read coefficients */
c0 = *(pb++);
/* Fetch 1 state variable */
x2 = *(px++);
/* Perform the multiply-accumulates */
acc0 += ((q63_t) x0 * c0);
acc1 += ((q63_t) x1 * c0);
acc2 += ((q63_t) x2 * c0);
/* Reuse the present sample states for next sample */
x0 = x1;
x1 = x2;
/* Decrement the loop counter */
i--;
}
/* Advance the state pointer by 3 to process the next group of 3 samples */
pState = pState + 3;
/* The results in the 3 accumulators are in 2.30 format. Convert to 1.31
** Then store the 3 outputs in the destination buffer. */
*pDst++ = (q31_t) (acc0 >> 31U);
*pDst++ = (q31_t) (acc1 >> 31U);
*pDst++ = (q31_t) (acc2 >> 31U);
/* Decrement the samples loop counter */
blkCnt--;
}
/* If the blockSize is not a multiple of 3, compute any remaining output samples here.
** No loop unrolling is used. */
while (blockSize > 0U)
{
/* Copy one sample at a time into state buffer */
*pStateCurnt++ = *pSrc++;
/* Set the accumulator to zero */
acc0 = 0;
/* Initialize state pointer */
px = pState;
/* Initialize Coefficient pointer */
pb = (pCoeffs);
i = numTaps;
/* Perform the multiply-accumulates */
do
{
acc0 += (q63_t) * (px++) * (*(pb++));
i--;
} while (i > 0U);
/* The result is in 2.62 format. Convert to 1.31
** Then store the output in the destination buffer. */
*pDst++ = (q31_t) (acc0 >> 31U);
/* Advance state pointer by 1 for the next sample */
pState = pState + 1;
/* Decrement the samples loop counter */
blockSize--;
}
/* Processing is complete.
** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
** This prepares the state buffer for the next function call. */
/* Points to the start of the state buffer */
pStateCurnt = S->pState;
tapCnt = (numTaps - 1U) >> 2U;
/* copy data */
while (tapCnt > 0U)
{
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
tapCnt--;
}
/* Calculate remaining number of copies */
tapCnt = (numTaps - 1U) % 0x4U;
/* Copy the remaining q31_t data */
while (tapCnt > 0U)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
tapCnt--;
}
#else
/* Run the below code for Cortex-M0 */
q31_t *px; /* Temporary pointer for state */
q31_t *pb; /* Temporary pointer for coefficient buffer */
q63_t acc; /* Accumulator */
uint32_t numTaps = S->numTaps; /* Length of the filter */
uint32_t i, tapCnt, blkCnt; /* Loop counters */
/* S->pState buffer contains previous frame (numTaps - 1) samples */
/* pStateCurnt points to the location where the new input data should be written */
pStateCurnt = &(S->pState[(numTaps - 1U)]);
/* Initialize blkCnt with blockSize */
blkCnt = blockSize;
while (blkCnt > 0U)
{
/* Copy one sample at a time into state buffer */
*pStateCurnt++ = *pSrc++;
/* Set the accumulator to zero */
acc = 0;
/* Initialize state pointer */
px = pState;
/* Initialize Coefficient pointer */
pb = pCoeffs;
i = numTaps;
/* Perform the multiply-accumulates */
do
{
/* acc = 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] */
acc += (q63_t) * px++ * *pb++;
i--;
} while (i > 0U);
/* The result is in 2.62 format. Convert to 1.31
** Then store the output in the destination buffer. */
*pDst++ = (q31_t) (acc >> 31U);
/* Advance state pointer by 1 for the next sample */
pState = pState + 1;
/* Decrement the samples loop counter */
blkCnt--;
}
/* Processing is complete.
** Now copy the last numTaps - 1 samples to the starting of the state buffer.
** This prepares the state buffer for the next function call. */
/* Points to the start of the state buffer */
pStateCurnt = S->pState;
/* Copy numTaps number of values */
tapCnt = numTaps - 1U;
/* Copy the data */
while (tapCnt > 0U)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
tapCnt--;
}
#endif /* #if defined (ARM_MATH_DSP) */
}
/**
* @} end of FIR group
*/