/* ----------------------------------------------------------------------
* 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_q31.c
*
* Description: Q31 FIR Decimator.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* 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.
* @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
* 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 (where log2 is read as log to the base 2).
* After all multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format.
*
* \par
* Refer to the function arm_fir_decimate_fast_q31() for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4.
*/
void arm_fir_decimate_q31(
const 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 */
q63_t sum0; /* Accumulator */
uint32_t numTaps = S->numTaps; /* Number of taps */
uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */
#ifndef ARM_MATH_CM0_FAMILY
/* Run the below code for Cortex-M4 and Cortex-M3 */
/* 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;
while(blkCnt > 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 += (q63_t) x0 *c0;
/* Read the b[numTaps-2] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-2] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 += (q63_t) x0 *c0;
/* Read the b[numTaps-3] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-3] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 += (q63_t) x0 *c0;
/* Read the b[numTaps-4] coefficient */
c0 = *(pb++);
/* Read x[n-numTaps-4] sample */
x0 = *(px++);
/* Perform the multiply-accumulate */
sum0 += (q63_t) 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 += (q63_t) 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;
/* The result is in the accumulator, store in the destination buffer. */
*pDst++ = (q31_t) (sum0 >> 31);
/* Decrement the loop counter */
blkCnt--;
}
/* 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--;
}
#else
/* Run the below code for Cortex-M0 */
/* 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;
while(blkCnt > 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;
tapCnt = numTaps;
while(tapCnt > 0u)
{
/* Read coefficients */
c0 = *pb++;
/* Fetch 1 state variable */
x0 = *px++;
/* Perform the multiply-accumulate */
sum0 += (q63_t) 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;
/* The result is in the accumulator, store in the destination buffer. */
*pDst++ = (q31_t) (sum0 >> 31);
/* Decrement the loop counter */
blkCnt--;
}
/* Processing is complete.
** Now copy the last numTaps - 1 samples to the start 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;
/* copy data */
while(i > 0u)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
i--;
}
#endif /* #ifndef ARM_MATH_CM0_FAMILY */
}
/**
* @} end of FIR_decimate group
*/