/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_fir_decimate_fast_q15.c
* Description: Fast Q15 FIR Decimator
*
* $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_decimate
* @{
*/
/**
* @brief Processing function for the Q15 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4.
* @param[in] *S points to an instance of the Q15 FIR decimator 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 input samples to process per call.
* @return none
*
* \par Restrictions
* If the silicon does not support unaligned memory access enable the macro UNALIGNED_SUPPORT_DISABLE
* In this case input, output, state buffers should be aligned by 32-bit
*
* Scaling and Overflow Behavior:
* \par
* This fast version uses a 32-bit accumulator with 2.30 format.
* The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.
* Thus, if the accumulator result overflows it wraps around and distorts the result.
* In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (log2 is read as log to the base 2).
* The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result.
*
* \par
* Refer to the function arm_fir_decimate_q15() for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion.
* Both the slow and the fast versions use the same instance structure.
* Use the function arm_fir_decimate_init_q15() to initialize the filter structure.
*/
#ifndef UNALIGNED_SUPPORT_DISABLE
void arm_fir_decimate_fast_q15(
const arm_fir_decimate_instance_q15 * S,
q15_t * pSrc,
q15_t * pDst,
uint32_t blockSize)
{
q15_t *pState = S->pState; /* State pointer */
q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
q15_t *pStateCurnt; /* Points to the current sample of the state */
q15_t *px; /* Temporary pointer for state buffer */
q15_t *pb; /* Temporary pointer coefficient buffer */
q31_t x0, x1, c0, c1; /* Temporary variables to hold state and coefficient values */
q31_t sum0; /* Accumulators */
q31_t acc0, acc1;
q15_t *px0, *px1;
uint32_t blkCntN3;
uint32_t numTaps = S->numTaps; /* Number of taps */
uint32_t i, blkCnt, tapCnt, outBlockSize = blockSize / S->M; /* 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);
/* Total number of output samples to be computed */
blkCnt = outBlockSize / 2;
blkCntN3 = outBlockSize - (2 * blkCnt);
while (blkCnt > 0U)
{
/* Copy decimation factor number of new input samples into the state buffer */
i = 2 * S->M;
do
{
*pStateCurnt++ = *pSrc++;
} while (--i);
/* Set accumulator to zero */
acc0 = 0;
acc1 = 0;
/* Initialize state pointer */
px0 = pState;
px1 = pState + S->M;
/* Initialize coeff pointer */
pb = pCoeffs;
/* Loop unrolling. Process 4 taps at a time. */
tapCnt = numTaps >> 2;
/* Loop over the number of taps. Unroll by a factor of 4.
** Repeat until we've computed numTaps-4 coefficients. */
while (tapCnt > 0U)
{
/* Read the Read b[numTaps-1] and b[numTaps-2] coefficients */
c0 = *__SIMD32(pb)++;
/* Read x[n-numTaps-1] and x[n-numTaps-2]sample */
x0 = *__SIMD32(px0)++;
x1 = *__SIMD32(px1)++;
/* Perform the multiply-accumulate */
acc0 = __SMLAD(x0, c0, acc0);
acc1 = __SMLAD(x1, c0, acc1);
/* Read the b[numTaps-3] and b[numTaps-4] coefficient */
c0 = *__SIMD32(pb)++;
/* Read x[n-numTaps-2] and x[n-numTaps-3] sample */
x0 = *__SIMD32(px0)++;
x1 = *__SIMD32(px1)++;
/* Perform the multiply-accumulate */
acc0 = __SMLAD(x0, c0, acc0);
acc1 = __SMLAD(x1, c0, acc1);
/* Decrement the loop counter */
tapCnt--;
}
/* If the filter length is not a multiple of 4, compute the remaining filter taps */
tapCnt = numTaps % 0x4U;
while (tapCnt > 0U)
{
/* Read coefficients */
c0 = *pb++;
/* Fetch 1 state variable */
x0 = *px0++;
x1 = *px1++;
/* Perform the multiply-accumulate */
acc0 = __SMLAD(x0, c0, acc0);
acc1 = __SMLAD(x1, c0, acc1);
/* Decrement the loop counter */
tapCnt--;
}
/* Advance the state pointer by the decimation factor
* to process the next group of decimation factor number samples */
pState = pState + S->M * 2;
/* Store filter output, smlad returns the values in 2.14 format */
/* so downsacle by 15 to get output in 1.15 */
*pDst++ = (q15_t) (__SSAT((acc0 >> 15), 16));
*pDst++ = (q15_t) (__SSAT((acc1 >> 15), 16));
/* Decrement the loop counter */
blkCnt--;
}
while (blkCntN3 > 0U)
{
/* Copy decimation factor number of new input samples into the state buffer */
i = S->M;
do
{
*pStateCurnt++ = *pSrc++;
} while (--i);
/*Set sum to zero */
sum0 = 0;
/* Initialize state pointer */
px = pState;
/* Initialize coeff pointer */
pb = pCoeffs;
/* Loop unrolling. Process 4 taps at a time. */
tapCnt = numTaps >> 2;
/* Loop over the number of taps. Unroll by a factor of 4.
** Repeat until we've computed numTaps-4 coefficients. */
while (tapCnt > 0U)
{
/* Read the Read b[numTaps-1] and b[numTaps-2] coefficients */
c0 = *__SIMD32(pb)++;
/* Read x[n-numTaps-1] and x[n-numTaps-2]sample */
x0 = *__SIMD32(px)++;
/* Read the b[numTaps-3] and b[numTaps-4] coefficient */
c1 = *__SIMD32(pb)++;
/* Perform the multiply-accumulate */
sum0 = __SMLAD(x0, c0, sum0);
/* Read x[n-numTaps-2] and x[n-numTaps-3] sample */
x0 = *__SIMD32(px)++;
/* Perform the multiply-accumulate */
sum0 = __SMLAD(x0, c1, sum0);
/* Decrement the loop counter */
tapCnt--;
}
/* If the filter length is not a multiple of 4, compute the remaining filter taps */
tapCnt = numTaps % 0x4U;
while (tapCnt > 0U)
{
/* Read coefficients */
c0 = *pb++;
/* Fetch 1 state variable */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 = __SMLAD(x0, c0, sum0);
/* Decrement the loop counter */
tapCnt--;
}
/* Advance the state pointer by the decimation factor
* to process the next group of decimation factor number samples */
pState = pState + S->M;
/* Store filter output, smlad returns the values in 2.14 format */
/* so downsacle by 15 to get output in 1.15 */
*pDst++ = (q15_t) (__SSAT((sum0 >> 15), 16));
/* Decrement the loop counter */
blkCntN3--;
}
/* 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;
i = (numTaps - 1U) >> 2U;
/* copy data */
while (i > 0U)
{
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
/* Decrement the loop counter */
i--;
}
i = (numTaps - 1U) % 0x04U;
/* copy data */
while (i > 0U)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
i--;
}
}
#else
void arm_fir_decimate_fast_q15(
const arm_fir_decimate_instance_q15 * S,
q15_t * pSrc,
q15_t * pDst,
uint32_t blockSize)
{
q15_t *pState = S->pState; /* State pointer */
q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
q15_t *pStateCurnt; /* Points to the current sample of the state */
q15_t *px; /* Temporary pointer for state buffer */
q15_t *pb; /* Temporary pointer coefficient buffer */
q15_t x0, x1, c0; /* Temporary variables to hold state and coefficient values */
q31_t sum0; /* Accumulators */
q31_t acc0, acc1;
q15_t *px0, *px1;
uint32_t blkCntN3;
uint32_t numTaps = S->numTaps; /* Number of taps */
uint32_t i, blkCnt, tapCnt, outBlockSize = blockSize / S->M; /* 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);
/* Total number of output samples to be computed */
blkCnt = outBlockSize / 2;
blkCntN3 = outBlockSize - (2 * blkCnt);
while (blkCnt > 0U)
{
/* Copy decimation factor number of new input samples into the state buffer */
i = 2 * S->M;
do
{
*pStateCurnt++ = *pSrc++;
} while (--i);
/* Set accumulator to zero */
acc0 = 0;
acc1 = 0;
/* Initialize state pointer */
px0 = pState;
px1 = pState + S->M;
/* Initialize coeff pointer */
pb = pCoeffs;
/* Loop unrolling. Process 4 taps at a time. */
tapCnt = numTaps >> 2;
/* Loop over the number of taps. Unroll by a factor of 4.
** Repeat until we've computed numTaps-4 coefficients. */
while (tapCnt > 0U)
{
/* Read the Read b[numTaps-1] coefficients */
c0 = *pb++;
/* Read x[n-numTaps-1] for sample 0 and for sample 1 */
x0 = *px0++;
x1 = *px1++;
/* Perform the multiply-accumulate */
acc0 += x0 * c0;
acc1 += x1 * c0;
/* Read the b[numTaps-2] coefficient */
c0 = *pb++;
/* Read x[n-numTaps-2] for sample 0 and sample 1 */
x0 = *px0++;
x1 = *px1++;
/* Perform the multiply-accumulate */
acc0 += x0 * c0;
acc1 += x1 * c0;
/* Read the b[numTaps-3] coefficients */
c0 = *pb++;
/* Read x[n-numTaps-3] for sample 0 and sample 1 */
x0 = *px0++;
x1 = *px1++;
/* Perform the multiply-accumulate */
acc0 += x0 * c0;
acc1 += x1 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *pb++;
/* Read x[n-numTaps-4] for sample 0 and sample 1 */
x0 = *px0++;
x1 = *px1++;
/* Perform the multiply-accumulate */
acc0 += x0 * c0;
acc1 += x1 * c0;
/* Decrement the loop counter */
tapCnt--;
}
/* If the filter length is not a multiple of 4, compute the remaining filter taps */
tapCnt = numTaps % 0x4U;
while (tapCnt > 0U)
{
/* Read coefficients */
c0 = *pb++;
/* Fetch 1 state variable */
x0 = *px0++;
x1 = *px1++;
/* Perform the multiply-accumulate */
acc0 += x0 * c0;
acc1 += x1 * c0;
/* Decrement the loop counter */
tapCnt--;
}
/* Advance the state pointer by the decimation factor
* to process the next group of decimation factor number samples */
pState = pState + S->M * 2;
/* Store filter output, smlad returns the values in 2.14 format */
/* so downsacle by 15 to get output in 1.15 */
*pDst++ = (q15_t) (__SSAT((acc0 >> 15), 16));
*pDst++ = (q15_t) (__SSAT((acc1 >> 15), 16));
/* Decrement the loop counter */
blkCnt--;
}
while (blkCntN3 > 0U)
{
/* Copy decimation factor number of new input samples into the state buffer */
i = S->M;
do
{
*pStateCurnt++ = *pSrc++;
} while (--i);
/*Set sum to zero */
sum0 = 0;
/* Initialize state pointer */
px = pState;
/* Initialize coeff pointer */
pb = pCoeffs;
/* Loop unrolling. Process 4 taps at a time. */
tapCnt = numTaps >> 2;
/* Loop over the number of taps. Unroll by a factor of 4.
** Repeat until we've computed numTaps-4 coefficients. */
while (tapCnt > 0U)
{
/* Read the Read b[numTaps-1] coefficients */
c0 = *pb++;
/* Read x[n-numTaps-1] and sample */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 += x0 * c0;
/* Read the b[numTaps-2] coefficient */
c0 = *pb++;
/* Read x[n-numTaps-2] and sample */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 += x0 * c0;
/* Read the b[numTaps-3] coefficients */
c0 = *pb++;
/* Read x[n-numTaps-3] sample */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 += x0 * c0;
/* Read the b[numTaps-4] coefficient */
c0 = *pb++;
/* Read x[n-numTaps-4] sample */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 += x0 * c0;
/* Decrement the loop counter */
tapCnt--;
}
/* If the filter length is not a multiple of 4, compute the remaining filter taps */
tapCnt = numTaps % 0x4U;
while (tapCnt > 0U)
{
/* Read coefficients */
c0 = *pb++;
/* Fetch 1 state variable */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 += x0 * c0;
/* Decrement the loop counter */
tapCnt--;
}
/* Advance the state pointer by the decimation factor
* to process the next group of decimation factor number samples */
pState = pState + S->M;
/* Store filter output, smlad returns the values in 2.14 format */
/* so downsacle by 15 to get output in 1.15 */
*pDst++ = (q15_t) (__SSAT((sum0 >> 15), 16));
/* Decrement the loop counter */
blkCntN3--;
}
/* 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;
i = (numTaps - 1U) >> 2U;
/* copy data */
while (i > 0U)
{
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
i--;
}
i = (numTaps - 1U) % 0x04U;
/* copy data */
while (i > 0U)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
i--;
}
}
#endif /* #ifndef UNALIGNED_SUPPORT_DISABLE */
/**
* @} end of FIR_decimate group
*/