File content as of revision 3:4098b9d3d571:

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_fir_lattice_f32.c
 * Description:  Processing function for the floating-point FIR Lattice 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
 */

/**
 * @defgroup FIR_Lattice Finite Impulse Response (FIR) Lattice Filters
 *
 * This set of functions implements Finite Impulse Response (FIR) lattice filters
 * for Q15, Q31 and floating-point data types.  Lattice filters are used in a
 * variety of adaptive filter applications.  The filter structure is feedforward and
 * the net impulse response is finite length.
 * The functions operate on blocks
 * of input and output data and each call to the function processes
 * <code>blockSize</code> samples through the filter.  <code>pSrc</code> and
 * <code>pDst</code> point to input and output arrays containing <code>blockSize</code> values.
 *
 * \par Algorithm:
 * \image html FIRLattice.gif "Finite Impulse Response Lattice filter"
 * The following difference equation is implemented:
 * <pre>
 *    f0[n] = g0[n] = x[n]
 *    fm[n] = fm-1[n] + km * gm-1[n-1] for m = 1, 2, ...M
 *    gm[n] = km * fm-1[n] + gm-1[n-1] for m = 1, 2, ...M
 *    y[n] = fM[n]
 * </pre>
 * \par
 * <code>pCoeffs</code> points to tha array of reflection coefficients of size <code>numStages</code>.
 * Reflection Coefficients are stored in the following order.
 * \par
 * <pre>
 *    {k1, k2, ..., kM}
 * </pre>
 * where M is number of stages
 * \par
 * <code>pState</code> points to a state array of size <code>numStages</code>.
 * The state variables (g values) hold previous inputs and are stored in the following order.
 * <pre>
 *    {g0[n], g1[n], g2[n] ...gM-1[n]}
 * </pre>
 * The state variables are updated after each block of data is processed; the coefficients are untouched.
 * \par Instance Structure
 * The coefficients and state variables for a filter are stored together in an instance data structure.
 * A separate instance structure must be defined for each filter.
 * Coefficient arrays may be shared among several instances while state variable arrays cannot be shared.
 * There are separate instance structure declarations for each of the 3 supported data types.
 *
 * \par Initialization Functions
 * There is also an associated initialization function for each data type.
 * The initialization function performs the following operations:
 * - Sets the values of the internal structure fields.
 * - Zeros out the values in the state buffer.
 * To do this manually without calling the init function, assign the follow subfields of the instance structure:
 * numStages, pCoeffs, pState. Also set all of the values in pState to zero.
 *
 * \par
 * Use of the initialization function is optional.
 * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
 * To place an instance structure into a const data section, the instance structure must be manually initialized.
 * Set the values in the state buffer to zeros and then manually initialize the instance structure as follows:
 * <pre>
 *arm_fir_lattice_instance_f32 S = {numStages, pState, pCoeffs};
 *arm_fir_lattice_instance_q31 S = {numStages, pState, pCoeffs};
 *arm_fir_lattice_instance_q15 S = {numStages, pState, pCoeffs};
 * </pre>
 * \par
 * where <code>numStages</code> is the number of stages in the filter; <code>pState</code> is the address of the state buffer;
 * <code>pCoeffs</code> is the address of the coefficient buffer.
 * \par Fixed-Point Behavior
 * Care must be taken when using the fixed-point versions of the FIR Lattice filter functions.
 * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
 * Refer to the function specific documentation below for usage guidelines.
 */

/**
 * @addtogroup FIR_Lattice
 * @{
 */


  /**
   * @brief Processing function for the floating-point FIR lattice filter.
   * @param[in]  *S        points to an instance of the floating-point FIR lattice 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 samples to process.
   * @return none.
   */

void arm_fir_lattice_f32(
  const arm_fir_lattice_instance_f32 * S,
  float32_t * pSrc,
  float32_t * pDst,
  uint32_t blockSize)
{
  float32_t *pState;                             /* State pointer */
  float32_t *pCoeffs = S->pCoeffs;               /* Coefficient pointer */
  float32_t *px;                                 /* temporary state pointer */
  float32_t *pk;                                 /* temporary coefficient pointer */


#if defined (ARM_MATH_DSP)

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

  float32_t fcurr1, fnext1, gcurr1, gnext1;      /* temporary variables for first sample in loop unrolling */
  float32_t fcurr2, fnext2, gnext2;              /* temporary variables for second sample in loop unrolling */
  float32_t fcurr3, fnext3, gnext3;              /* temporary variables for third sample in loop unrolling */
  float32_t fcurr4, fnext4, gnext4;              /* temporary variables for fourth sample in loop unrolling */
  uint32_t numStages = S->numStages;             /* Number of stages in the filter */
  uint32_t blkCnt, stageCnt;                     /* temporary variables for counts */

  gcurr1 = 0.0f;
  pState = &S->pState[0];

  blkCnt = blockSize >> 2;

  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
     a second loop below computes the remaining 1 to 3 samples. */
  while (blkCnt > 0U)
  {

    /* Read two samples from input buffer */
    /* f0(n) = x(n) */
    fcurr1 = *pSrc++;
    fcurr2 = *pSrc++;

    /* Initialize coeff pointer */
    pk = (pCoeffs);

    /* Initialize state pointer */
    px = pState;

    /* Read g0(n-1) from state */
    gcurr1 = *px;

    /* Process first sample for first tap */
    /* f1(n) = f0(n) +  K1 * g0(n-1) */
    fnext1 = fcurr1 + ((*pk) * gcurr1);
    /* g1(n) = f0(n) * K1  +  g0(n-1) */
    gnext1 = (fcurr1 * (*pk)) + gcurr1;

    /* Process second sample for first tap */
    /* for sample 2 processing */
    fnext2 = fcurr2 + ((*pk) * fcurr1);
    gnext2 = (fcurr2 * (*pk)) + fcurr1;

    /* Read next two samples from input buffer */
    /* f0(n+2) = x(n+2) */
    fcurr3 = *pSrc++;
    fcurr4 = *pSrc++;

    /* Copy only last input samples into the state buffer
       which will be used for next four samples processing */
    *px++ = fcurr4;

    /* Process third sample for first tap */
    fnext3 = fcurr3 + ((*pk) * fcurr2);
    gnext3 = (fcurr3 * (*pk)) + fcurr2;

    /* Process fourth sample for first tap */
    fnext4 = fcurr4 + ((*pk) * fcurr3);
    gnext4 = (fcurr4 * (*pk++)) + fcurr3;

    /* Update of f values for next coefficient set processing */
    fcurr1 = fnext1;
    fcurr2 = fnext2;
    fcurr3 = fnext3;
    fcurr4 = fnext4;

    /* Loop unrolling.  Process 4 taps at a time . */
    stageCnt = (numStages - 1U) >> 2U;

    /* Loop over the number of taps.  Unroll by a factor of 4.
     ** Repeat until we've computed numStages-3 coefficients. */

    /* Process 2nd, 3rd, 4th and 5th taps ... here */
    while (stageCnt > 0U)
    {
      /* Read g1(n-1), g3(n-1) .... from state */
      gcurr1 = *px;

      /* save g1(n) in state buffer */
      *px++ = gnext4;

      /* Process first sample for 2nd, 6th .. tap */
      /* Sample processing for K2, K6.... */
      /* f2(n) = f1(n) +  K2 * g1(n-1) */
      fnext1 = fcurr1 + ((*pk) * gcurr1);
      /* Process second sample for 2nd, 6th .. tap */
      /* for sample 2 processing */
      fnext2 = fcurr2 + ((*pk) * gnext1);
      /* Process third sample for 2nd, 6th .. tap */
      fnext3 = fcurr3 + ((*pk) * gnext2);
      /* Process fourth sample for 2nd, 6th .. tap */
      fnext4 = fcurr4 + ((*pk) * gnext3);

      /* g2(n) = f1(n) * K2  +  g1(n-1) */
      /* Calculation of state values for next stage */
      gnext4 = (fcurr4 * (*pk)) + gnext3;
      gnext3 = (fcurr3 * (*pk)) + gnext2;
      gnext2 = (fcurr2 * (*pk)) + gnext1;
      gnext1 = (fcurr1 * (*pk++)) + gcurr1;


      /* Read g2(n-1), g4(n-1) .... from state */
      gcurr1 = *px;

      /* save g2(n) in state buffer */
      *px++ = gnext4;

      /* Sample processing for K3, K7.... */
      /* Process first sample for 3rd, 7th .. tap */
      /* f3(n) = f2(n) +  K3 * g2(n-1) */
      fcurr1 = fnext1 + ((*pk) * gcurr1);
      /* Process second sample for 3rd, 7th .. tap */
      fcurr2 = fnext2 + ((*pk) * gnext1);
      /* Process third sample for 3rd, 7th .. tap */
      fcurr3 = fnext3 + ((*pk) * gnext2);
      /* Process fourth sample for 3rd, 7th .. tap */
      fcurr4 = fnext4 + ((*pk) * gnext3);

      /* Calculation of state values for next stage */
      /* g3(n) = f2(n) * K3  +  g2(n-1) */
      gnext4 = (fnext4 * (*pk)) + gnext3;
      gnext3 = (fnext3 * (*pk)) + gnext2;
      gnext2 = (fnext2 * (*pk)) + gnext1;
      gnext1 = (fnext1 * (*pk++)) + gcurr1;


      /* Read g1(n-1), g3(n-1) .... from state */
      gcurr1 = *px;

      /* save g3(n) in state buffer */
      *px++ = gnext4;

      /* Sample processing for K4, K8.... */
      /* Process first sample for 4th, 8th .. tap */
      /* f4(n) = f3(n) +  K4 * g3(n-1) */
      fnext1 = fcurr1 + ((*pk) * gcurr1);
      /* Process second sample for 4th, 8th .. tap */
      /* for sample 2 processing */
      fnext2 = fcurr2 + ((*pk) * gnext1);
      /* Process third sample for 4th, 8th .. tap */
      fnext3 = fcurr3 + ((*pk) * gnext2);
      /* Process fourth sample for 4th, 8th .. tap */
      fnext4 = fcurr4 + ((*pk) * gnext3);

      /* g4(n) = f3(n) * K4  +  g3(n-1) */
      /* Calculation of state values for next stage */
      gnext4 = (fcurr4 * (*pk)) + gnext3;
      gnext3 = (fcurr3 * (*pk)) + gnext2;
      gnext2 = (fcurr2 * (*pk)) + gnext1;
      gnext1 = (fcurr1 * (*pk++)) + gcurr1;

      /* Read g2(n-1), g4(n-1) .... from state */
      gcurr1 = *px;

      /* save g4(n) in state buffer */
      *px++ = gnext4;

      /* Sample processing for K5, K9.... */
      /* Process first sample for 5th, 9th .. tap */
      /* f5(n) = f4(n) +  K5 * g4(n-1) */
      fcurr1 = fnext1 + ((*pk) * gcurr1);
      /* Process second sample for 5th, 9th .. tap */
      fcurr2 = fnext2 + ((*pk) * gnext1);
      /* Process third sample for 5th, 9th .. tap */
      fcurr3 = fnext3 + ((*pk) * gnext2);
      /* Process fourth sample for 5th, 9th .. tap */
      fcurr4 = fnext4 + ((*pk) * gnext3);

      /* Calculation of state values for next stage */
      /* g5(n) = f4(n) * K5  +  g4(n-1) */
      gnext4 = (fnext4 * (*pk)) + gnext3;
      gnext3 = (fnext3 * (*pk)) + gnext2;
      gnext2 = (fnext2 * (*pk)) + gnext1;
      gnext1 = (fnext1 * (*pk++)) + gcurr1;

      stageCnt--;
    }

    /* If the (filter length -1) is not a multiple of 4, compute the remaining filter taps */
    stageCnt = (numStages - 1U) % 0x4U;

    while (stageCnt > 0U)
    {
      gcurr1 = *px;

      /* save g value in state buffer */
      *px++ = gnext4;

      /* Process four samples for last three taps here */
      fnext1 = fcurr1 + ((*pk) * gcurr1);
      fnext2 = fcurr2 + ((*pk) * gnext1);
      fnext3 = fcurr3 + ((*pk) * gnext2);
      fnext4 = fcurr4 + ((*pk) * gnext3);

      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext4 = (fcurr4 * (*pk)) + gnext3;
      gnext3 = (fcurr3 * (*pk)) + gnext2;
      gnext2 = (fcurr2 * (*pk)) + gnext1;
      gnext1 = (fcurr1 * (*pk++)) + gcurr1;

      /* Update of f values for next coefficient set processing */
      fcurr1 = fnext1;
      fcurr2 = fnext2;
      fcurr3 = fnext3;
      fcurr4 = fnext4;

      stageCnt--;

    }

    /* The results in the 4 accumulators, store in the destination buffer. */
    /* y(n) = fN(n) */
    *pDst++ = fcurr1;
    *pDst++ = fcurr2;
    *pDst++ = fcurr3;
    *pDst++ = fcurr4;

    blkCnt--;
  }

  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
   ** No loop unrolling is used. */
  blkCnt = blockSize % 0x4U;

  while (blkCnt > 0U)
  {
    /* f0(n) = x(n) */
    fcurr1 = *pSrc++;

    /* Initialize coeff pointer */
    pk = (pCoeffs);

    /* Initialize state pointer */
    px = pState;

    /* read g2(n) from state buffer */
    gcurr1 = *px;

    /* for sample 1 processing */
    /* f1(n) = f0(n) +  K1 * g0(n-1) */
    fnext1 = fcurr1 + ((*pk) * gcurr1);
    /* g1(n) = f0(n) * K1  +  g0(n-1) */
    gnext1 = (fcurr1 * (*pk++)) + gcurr1;

    /* save g1(n) in state buffer */
    *px++ = fcurr1;

    /* f1(n) is saved in fcurr1
       for next stage processing */
    fcurr1 = fnext1;

    stageCnt = (numStages - 1U);

    /* stage loop */
    while (stageCnt > 0U)
    {
      /* read g2(n) from state buffer */
      gcurr1 = *px;

      /* save g1(n) in state buffer */
      *px++ = gnext1;

      /* Sample processing for K2, K3.... */
      /* f2(n) = f1(n) +  K2 * g1(n-1) */
      fnext1 = fcurr1 + ((*pk) * gcurr1);
      /* g2(n) = f1(n) * K2  +  g1(n-1) */
      gnext1 = (fcurr1 * (*pk++)) + gcurr1;

      /* f1(n) is saved in fcurr1
         for next stage processing */
      fcurr1 = fnext1;

      stageCnt--;

    }

    /* y(n) = fN(n) */
    *pDst++ = fcurr1;

    blkCnt--;

  }

#else

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

  float32_t fcurr, fnext, gcurr, gnext;          /* temporary variables */
  uint32_t numStages = S->numStages;             /* Length of the filter */
  uint32_t blkCnt, stageCnt;                     /* temporary variables for counts */

  pState = &S->pState[0];

  blkCnt = blockSize;

  while (blkCnt > 0U)
  {
    /* f0(n) = x(n) */
    fcurr = *pSrc++;

    /* Initialize coeff pointer */
    pk = pCoeffs;

    /* Initialize state pointer */
    px = pState;

    /* read g0(n-1) from state buffer */
    gcurr = *px;

    /* for sample 1 processing */
    /* f1(n) = f0(n) +  K1 * g0(n-1) */
    fnext = fcurr + ((*pk) * gcurr);
    /* g1(n) = f0(n) * K1  +  g0(n-1) */
    gnext = (fcurr * (*pk++)) + gcurr;

    /* save f0(n) in state buffer */
    *px++ = fcurr;

    /* f1(n) is saved in fcurr
       for next stage processing */
    fcurr = fnext;

    stageCnt = (numStages - 1U);

    /* stage loop */
    while (stageCnt > 0U)
    {
      /* read g2(n) from state buffer */
      gcurr = *px;

      /* save g1(n) in state buffer */
      *px++ = gnext;

      /* Sample processing for K2, K3.... */
      /* f2(n) = f1(n) +  K2 * g1(n-1) */
      fnext = fcurr + ((*pk) * gcurr);
      /* g2(n) = f1(n) * K2  +  g1(n-1) */
      gnext = (fcurr * (*pk++)) + gcurr;

      /* f1(n) is saved in fcurr1
         for next stage processing */
      fcurr = fnext;

      stageCnt--;

    }

    /* y(n) = fN(n) */
    *pDst++ = fcurr;

    blkCnt--;

  }

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

}

/**
 * @} end of FIR_Lattice group
 */