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-/* ----------------------------------------------------------------------
-* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
-*
-* $Date: 19. March 2015
-* $Revision: V.1.4.5
-*
-* 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
- *
- * <b>Scaling and Overflow Behavior:</b>
- * \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 <code>arm_fir_decimate_fast_q31()</code> 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
- */
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