arm_fir_decimate_f32.c

/* ----------------------------------------------------------------------    
* 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_f32.c    
*    
* Description:	FIR decimation for floating-point sequences.    
*    
* 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
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*   - Redistributions in binary form must reproduce the above copyright
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*     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
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* -------------------------------------------------------------------- */

#include "arm_math.h"

/**    
 * @ingroup groupFilters    
 */

/**    
 * @defgroup FIR_decimate Finite Impulse Response (FIR) Decimator    
 *    
 * These functions combine an FIR filter together with a decimator.    
 * They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.    
 * Conceptually, the functions are equivalent to the block diagram below:    
 * \image html FIRDecimator.gif "Components included in the FIR Decimator functions"    
 * When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized    
 * cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.    
 * The user of the function is responsible for providing the filter coefficients.    
 *    
 * The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.    
 * Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the    
 * samples output by the decimator are computed.    
 * The functions operate on blocks of input and output data.    
 * <code>pSrc</code> points to an array of <code>blockSize</code> input values and    
 * <code>pDst</code> points to an array of <code>blockSize/M</code> output values.    
 * In order to have an integer number of output samples <code>blockSize</code>    
 * must always be a multiple of the decimation factor <code>M</code>.    
 *    
 * The library provides separate functions for Q15, Q31 and floating-point data types.    
 *    
 * \par Algorithm:    
 * The FIR portion of the algorithm uses the standard form filter:    
 * <pre>    
 *    y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]    
 * </pre>    
 * where, <code>b[n]</code> are the filter coefficients.    
 * \par   
 * The <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.    
 * Coefficients are stored in time reversed order.    
 * \par    
 * <pre>    
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}    
 * </pre>    
 * \par    
 * <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.    
 * Samples in the state buffer are stored in the order:    
 * \par    
 * <pre>    
 *    {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}    
 * </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 array should be allocated separately.    
 * 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.    
 * - Checks to make sure that the size of the input is a multiple of the decimation factor.    
 * To do this manually without calling the init function, assign the follow subfields of the instance structure:
 * numTaps, pCoeffs, M (decimation factor), 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.    
 * The code below statically initializes each of the 3 different data type filter instance structures    
 * <pre>    
 *arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};    
 *arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};    
 *arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};    
 * </pre>    
 * where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;    
 * <code>pCoeffs</code> is the address of the coefficient buffer;    
 * <code>pState</code> is the address of the state buffer.    
 * Be sure to set the values in the state buffer to zeros when doing static initialization.    
 *    
 * \par Fixed-Point Behavior    
 * Care must be taken when using the fixed-point versions of the FIR decimate 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_decimate    
 * @{    
 */

  /**    
   * @brief Processing function for the floating-point FIR decimator.    
   * @param[in] *S        points to an instance of the floating-point 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.    
   */

void arm_fir_decimate_f32(
  const arm_fir_decimate_instance_f32 * S,
  float32_t * pSrc,
  float32_t * pDst,
  uint32_t blockSize)
{
  float32_t *pState = S->pState;                 /* State pointer */
  float32_t *pCoeffs = S->pCoeffs;               /* Coefficient pointer */
  float32_t *pStateCurnt;                        /* Points to the current sample of the state */
  float32_t *px, *pb;                            /* Temporary pointers for state and coefficient buffers */
  float32_t sum0;                                /* Accumulator */
  float32_t x0, c0;                              /* Temporary variables to hold state and coefficient values */
  uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
  uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */

#ifndef ARM_MATH_CM0_FAMILY

  uint32_t blkCntN4;
  float32_t *px0, *px1, *px2, *px3;
  float32_t acc0, acc1, acc2, acc3;
  float32_t x1, x2, x3;

  /* 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 / 4;
  blkCntN4 = outBlockSize - (4 * blkCnt);

  while(blkCnt > 0u)
  {
    /* Copy 4 * decimation factor number of new input samples into the state buffer */
    i = 4 * S->M;

    do
    {
      *pStateCurnt++ = *pSrc++;

    } while(--i);

    /* Set accumulators to zero */
    acc0 = 0.0f;
    acc1 = 0.0f;
    acc2 = 0.0f;
    acc3 = 0.0f;

    /* Initialize state pointer for all the samples */
    px0 = pState;
    px1 = pState + S->M;
    px2 = pState + 2 * S->M;
    px3 = pState + 3 * S->M;

    /* 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 for acc0 */
      x0 = *(px0++);
      /* Read x[n-numTaps-1] sample for acc1 */
      x1 = *(px1++);
      /* Read x[n-numTaps-1] sample for acc2 */
      x2 = *(px2++);
      /* Read x[n-numTaps-1] sample for acc3 */
      x3 = *(px3++);

      /* Perform the multiply-accumulate */
      acc0 += x0 * c0;
      acc1 += x1 * c0;
      acc2 += x2 * c0;
      acc3 += x3 * c0;

      /* Read the b[numTaps-2] coefficient */
      c0 = *(pb++);

      /* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */
      x0 = *(px0++);
      x1 = *(px1++);
      x2 = *(px2++);
      x3 = *(px3++);

      /* Perform the multiply-accumulate */
      acc0 += x0 * c0;
      acc1 += x1 * c0;
      acc2 += x2 * c0;
      acc3 += x3 * c0;

      /* Read the b[numTaps-3] coefficient */
      c0 = *(pb++);

      /* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */
      x0 = *(px0++);
      x1 = *(px1++);
      x2 = *(px2++);
      x3 = *(px3++);

      /* Perform the multiply-accumulate */
      acc0 += x0 * c0;
      acc1 += x1 * c0;
      acc2 += x2 * c0;
      acc3 += x3 * c0;

      /* Read the b[numTaps-4] coefficient */
      c0 = *(pb++);

      /* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */
      x0 = *(px0++);
      x1 = *(px1++);
      x2 = *(px2++);
      x3 = *(px3++);

      /* Perform the multiply-accumulate */
      acc0 += x0 * c0;
      acc1 += x1 * c0;
      acc2 += x2 * c0;
      acc3 += x3 * 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  state variables for acc0, acc1, acc2, acc3 */
      x0 = *(px0++);
      x1 = *(px1++);
      x2 = *(px2++);
      x3 = *(px3++);

      /* Perform the multiply-accumulate */
      acc0 += x0 * c0;
      acc1 += x1 * c0;
      acc2 += x2 * c0;
      acc3 += x3 * 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 + 4 * S->M;

    /* The result is in the accumulator, store in the destination buffer. */
    *pDst++ = acc0;
    *pDst++ = acc1;
    *pDst++ = acc2;
    *pDst++ = acc3;

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

  while(blkCntN4 > 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 = 0.0f;

    /* 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 += x0 * c0;

      /* Read the b[numTaps-2] coefficient */
      c0 = *(pb++);

      /* Read x[n-numTaps-2] sample */
      x0 = *(px++);

      /* Perform the multiply-accumulate */
      sum0 += x0 * c0;

      /* Read the b[numTaps-3] coefficient */
      c0 = *(pb++);

      /* Read x[n-numTaps-3] sample */
      x0 = *(px++);

      /* Perform the multiply-accumulate */
      sum0 += x0 * c0;

      /* Read the b[numTaps-4] coefficient */
      c0 = *(pb++);

      /* Read x[n-numTaps-4] sample */
      x0 = *(px++);

      /* Perform the multiply-accumulate */
      sum0 += 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 += 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++ = sum0;

    /* Decrement the loop counter */
    blkCntN4--;
  }

  /* 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) >> 2;

  /* 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 = 0.0f;

    /* 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 += 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++ = sum0;

    /* 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;

  /* Copy numTaps number of values */
  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    
 */