DSP_Lib/Source/FilteringFunctions/arm_fir_decimate_q31.c - third_party/github/STMicroelectronics/cmsis_core - Git at Google

 /* ----------------------------------------------------------------------
 * 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
  */
	/* ----------------------------------------------------------------------
	* 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
	*/