/* ----------------------------------------------------------------------
* Copyright (C) 2010-2013 ARM Limited. All rights reserved.
*
* $Date: 17. January 2013
* $Revision: V1.4.1
*
* Project: CMSIS DSP Library
* Title: arm_fir_decimate_fast_q31.c
*
* Description: Fast Q31 FIR Decimator.
*
* Target Processor: Cortex-M4/Cortex-M3
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* - Neither the name of ARM LIMITED nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */
#include "arm_math.h"
/**
* @ingroup groupFilters
*/
/**
* @addtogroup FIR_decimate
* @{
*/
/**
* @brief Processing function for the Q31 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4.
* @param[in] *S points to an instance of the Q31 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
*
* Scaling and Overflow Behavior:
*
* \par
* This function is optimized for speed at the expense of fixed-point precision and overflow protection.
* The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format.
* These intermediate results are added to a 2.30 accumulator.
* Finally, the accumulator is saturated and converted to a 1.31 result.
* 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.
* In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (where log2 is read as log to the base 2).
*
* \par
* Refer to the function arm_fir_decimate_q31() 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.
* Use the function arm_fir_decimate_init_q31() to initialize the filter structure.
*/
void arm_fir_decimate_fast_q31(
arm_fir_decimate_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 */
q31_t x0, c0; /* Temporary variables to hold state and coefficient values */
q31_t *px; /* Temporary pointers for state buffer */
q31_t *pb; /* Temporary pointers for coefficient buffer */
q31_t sum0; /* Accumulator */
uint32_t numTaps = S->numTaps; /* Number of taps */
uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
uint32_t blkCntN2;
q31_t x1;
q31_t acc0, acc1;
q31_t *px0, *px1;
/* 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;
blkCntN2 = 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 b[numTaps-1] coefficient */
c0 = *(pb);
/* Read x[n-numTaps-1] for sample 0 sample 1 */
x0 = *(px0);
x1 = *(px1);
/* Perform the multiply-accumulate */
acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
/* Read the b[numTaps-2] coefficient */
c0 = *(pb + 1u);
/* Read x[n-numTaps-2] for sample 0 sample 1 */
x0 = *(px0 + 1u);
x1 = *(px1 + 1u);
/* Perform the multiply-accumulate */
acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
/* Read the b[numTaps-3] coefficient */
c0 = *(pb + 2u);
/* Read x[n-numTaps-3] for sample 0 sample 1 */
x0 = *(px0 + 2u);
x1 = *(px1 + 2u);
pb += 4u;
/* Perform the multiply-accumulate */
acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
/* Read the b[numTaps-4] coefficient */
c0 = *(pb - 1u);
/* Read x[n-numTaps-4] for sample 0 sample 1 */
x0 = *(px0 + 3u);
x1 = *(px1 + 3u);
/* Perform the multiply-accumulate */
acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
/* update state pointers */
px0 += 4u;
px1 += 4u;
/* 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 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
/* 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;
/* The result is in the accumulator, store in the destination buffer. */
*pDst++ = (q31_t) (acc0 << 1);
*pDst++ = (q31_t) (acc1 << 1);
/* Decrement the loop counter */
blkCnt--;
}
while(blkCntN2 > 0u)
{
/* Copy decimation factor number of new input samples into the state buffer */
i = S->M;
do
{
*pStateCurnt++ = *pSrc++;
} while(--i);
/* Set accumulator 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 b[numTaps-1] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-1] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
/* Read the b[numTaps-2] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-2] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
/* Read the b[numTaps-3] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-3] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-4] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
/* 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 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
/* 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;
/* The result is in the accumulator, store in the destination buffer. */
*pDst++ = (q31_t) (sum0 << 1);
/* Decrement the loop counter */
blkCntN2--;
}
/* 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--;
}
}
/**
* @} end of FIR_decimate group
*/