text: /* ----------------------------------------------------------------------    
  * Copyright (C) 2010-2013 ARM Limited. All rights reserved.    
  *    
  * $Date:        17. January 2013
  * $Revision: 	V1.4.1
  *    
  * 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
  * 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    
   */
  
  /**    
   * @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    
   */
  