DSP/Source/FilteringFunctions/arm_lms_q15.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_lms_q15.c
 * Description:  Processing function for the Q15 LMS filter
 *
 * $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 LMS
 * @{
 */

 /**
 * @brief Processing function for Q15 LMS filter.
 * @param[in] *S points to an instance of the Q15 LMS filter structure.
 * @param[in] *pSrc points to the block of input data.
 * @param[in] *pRef points to the block of reference data.
 * @param[out] *pOut points to the block of output data.
 * @param[out] *pErr points to the block of error data.
 * @param[in] blockSize number of samples to process.
 * @return none.
 *
 * \par Scaling and Overflow Behavior:
 * The function is implemented using a 64-bit internal accumulator.
 * Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result.
 * The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format.
 * There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved.
 * After all additions have been performed, the accumulator is truncated to 34.15 format by discarding low 15 bits.
 * Lastly, the accumulator is saturated to yield a result in 1.15 format.
 *
 * \par
 * 	In this filter, filter coefficients are updated for each sample and the updation of filter cofficients are saturted.
 *
 */

void arm_lms_q15(
  const arm_lms_instance_q15 * S,
  q15_t * pSrc,
  q15_t * pRef,
  q15_t * pOut,
  q15_t * pErr,
  uint32_t blockSize)
{
  q15_t *pState = S->pState;                     /* State pointer */
  uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
  q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
  q15_t *pStateCurnt;                            /* Points to the current sample of the state */
  q15_t mu = S->mu;                              /* Adaptive factor */
  q15_t *px;                                     /* Temporary pointer for state */
  q15_t *pb;                                     /* Temporary pointer for coefficient buffer */
  uint32_t tapCnt, blkCnt;                       /* Loop counters */
  q63_t acc;                                     /* Accumulator */
  q15_t e = 0;                                   /* error of data sample */
  q15_t alpha;                                   /* Intermediate constant for taps update */
  q31_t coef;                                    /* Teporary variable for coefficient */
  q31_t acc_l, acc_h;
  int32_t lShift = (15 - (int32_t) S->postShift);       /*  Post shift  */
  int32_t uShift = (32 - lShift);


#if defined (ARM_MATH_DSP)

  /* Run the below code for Cortex-M4 and Cortex-M3 */


  /* S->pState points to buffer which contains previous frame (numTaps - 1) samples */
  /* pStateCurnt points to the location where the new input data should be written */
  pStateCurnt = &(S->pState[(numTaps - 1U)]);

  /* Initializing blkCnt with blockSize */
  blkCnt = blockSize;

  while (blkCnt > 0U)
  {
    /* Copy the new input sample into the state buffer */
    *pStateCurnt++ = *pSrc++;

    /* Initialize state pointer */
    px = pState;

    /* Initialize coefficient pointer */
    pb = pCoeffs;

    /* Set the accumulator to zero */
    acc = 0;

    /* Loop unrolling.  Process 4 taps at a time. */
    tapCnt = numTaps >> 2U;

    while (tapCnt > 0U)
    {
      /* acc +=  b[N] * x[n-N] + b[N-1] * x[n-N-1] */
      /* Perform the multiply-accumulate */
#ifndef UNALIGNED_SUPPORT_DISABLE

      acc = __SMLALD(*__SIMD32(px)++, (*__SIMD32(pb)++), acc);
      acc = __SMLALD(*__SIMD32(px)++, (*__SIMD32(pb)++), acc);

#else

      acc += (q63_t) (((q31_t) (*px++) * (*pb++)));
      acc += (q63_t) (((q31_t) (*px++) * (*pb++)));
      acc += (q63_t) (((q31_t) (*px++) * (*pb++)));
      acc += (q63_t) (((q31_t) (*px++) * (*pb++)));


#endif	/*	#ifndef UNALIGNED_SUPPORT_DISABLE	*/

      /* 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)
    {
      /* Perform the multiply-accumulate */
      acc += (q63_t) (((q31_t) (*px++) * (*pb++)));

      /* Decrement the loop counter */
      tapCnt--;
    }

    /* Calc lower part of acc */
    acc_l = acc & 0xffffffff;

    /* Calc upper part of acc */
    acc_h = (acc >> 32) & 0xffffffff;

    /* Apply shift for lower part of acc and upper part of acc */
    acc = (uint32_t) acc_l >> lShift | acc_h << uShift;

    /* Converting the result to 1.15 format and saturate the output */
    acc = __SSAT(acc, 16);

    /* Store the result from accumulator into the destination buffer. */
    *pOut++ = (q15_t) acc;

    /* Compute and store error */
    e = *pRef++ - (q15_t) acc;

    *pErr++ = (q15_t) e;

    /* Compute alpha i.e. intermediate constant for taps update */
    alpha = (q15_t) (((q31_t) e * (mu)) >> 15);

    /* Initialize state pointer */
    /* Advance state pointer by 1 for the next sample */
    px = pState++;

    /* Initialize coefficient pointer */
    pb = pCoeffs;

    /* Loop unrolling.  Process 4 taps at a time. */
    tapCnt = numTaps >> 2U;

    /* Update filter coefficients */
    while (tapCnt > 0U)
    {
      coef = (q31_t) * pb + (((q31_t) alpha * (*px++)) >> 15);
      *pb++ = (q15_t) __SSAT((coef), 16);
      coef = (q31_t) * pb + (((q31_t) alpha * (*px++)) >> 15);
      *pb++ = (q15_t) __SSAT((coef), 16);
      coef = (q31_t) * pb + (((q31_t) alpha * (*px++)) >> 15);
      *pb++ = (q15_t) __SSAT((coef), 16);
      coef = (q31_t) * pb + (((q31_t) alpha * (*px++)) >> 15);
      *pb++ = (q15_t) __SSAT((coef), 16);

      /* 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)
    {
      /* Perform the multiply-accumulate */
      coef = (q31_t) * pb + (((q31_t) alpha * (*px++)) >> 15);
      *pb++ = (q15_t) __SSAT((coef), 16);

      /* Decrement the loop counter */
      tapCnt--;
    }

    /* 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 pState buffer */
  pStateCurnt = S->pState;

  /* Calculation of count for copying integer writes */
  tapCnt = (numTaps - 1U) >> 2;

  while (tapCnt > 0U)
  {

#ifndef UNALIGNED_SUPPORT_DISABLE

    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
#else
    *pStateCurnt++ = *pState++;
    *pStateCurnt++ = *pState++;
    *pStateCurnt++ = *pState++;
    *pStateCurnt++ = *pState++;
#endif

    tapCnt--;

  }

  /* Calculation of count for remaining q15_t data */
  tapCnt = (numTaps - 1U) % 0x4U;

  /* copy data */
  while (tapCnt > 0U)
  {
    *pStateCurnt++ = *pState++;

    /* Decrement the loop counter */
    tapCnt--;
  }

#else

  /* Run the below code for Cortex-M0 */

  /* S->pState points to buffer which contains previous frame (numTaps - 1) samples */
  /* pStateCurnt points to the location where the new input data should be written */
  pStateCurnt = &(S->pState[(numTaps - 1U)]);

  /* Loop over blockSize number of values */
  blkCnt = blockSize;

  while (blkCnt > 0U)
  {
    /* Copy the new input sample into the state buffer */
    *pStateCurnt++ = *pSrc++;

    /* Initialize pState pointer */
    px = pState;

    /* Initialize pCoeffs pointer */
    pb = pCoeffs;

    /* Set the accumulator to zero */
    acc = 0;

    /* Loop over numTaps number of values */
    tapCnt = numTaps;

    while (tapCnt > 0U)
    {
      /* Perform the multiply-accumulate */
      acc += (q63_t) ((q31_t) (*px++) * (*pb++));

      /* Decrement the loop counter */
      tapCnt--;
    }

    /* Calc lower part of acc */
    acc_l = acc & 0xffffffff;

    /* Calc upper part of acc */
    acc_h = (acc >> 32) & 0xffffffff;

    /* Apply shift for lower part of acc and upper part of acc */
    acc = (uint32_t) acc_l >> lShift | acc_h << uShift;

    /* Converting the result to 1.15 format and saturate the output */
    acc = __SSAT(acc, 16);

    /* Store the result from accumulator into the destination buffer. */
    *pOut++ = (q15_t) acc;

    /* Compute and store error */
    e = *pRef++ - (q15_t) acc;

    *pErr++ = (q15_t) e;

    /* Compute alpha i.e. intermediate constant for taps update */
    alpha = (q15_t) (((q31_t) e * (mu)) >> 15);

    /* Initialize pState pointer */
    /* Advance state pointer by 1 for the next sample */
    px = pState++;

    /* Initialize pCoeffs pointer */
    pb = pCoeffs;

    /* Loop over numTaps number of values */
    tapCnt = numTaps;

    while (tapCnt > 0U)
    {
      /* Perform the multiply-accumulate */
      coef = (q31_t) * pb + (((q31_t) alpha * (*px++)) >> 15);
      *pb++ = (q15_t) __SSAT((coef), 16);

      /* Decrement the loop counter */
      tapCnt--;
    }

    /* 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 pState buffer */
  pStateCurnt = S->pState;

  /*  Copy (numTaps - 1U) samples  */
  tapCnt = (numTaps - 1U);

  /* Copy the data */
  while (tapCnt > 0U)
  {
    *pStateCurnt++ = *pState++;

    /* Decrement the loop counter */
    tapCnt--;
  }

#endif /*   #if defined (ARM_MATH_DSP) */

}

/**
   * @} end of LMS group
   */