File content as of revision 1:fdd22bb7aa52:

/* ----------------------------------------------------------------------    
* Copyright (C) 2010 ARM Limited. All rights reserved.    
*    
* $Date:        15. February 2012  
* $Revision:     V1.1.0  
*    
* Project:         CMSIS DSP Library    
* Title:        arm_fir_sparse_q31.c    
*    
* Description:    Q31 sparse FIR filter processing function.   
*    
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
* Version 1.1.0 2012/02/15 
*    Updated with more optimizations, bug fixes and minor API changes.  
*   
* Version 1.0.10 2011/7/15  
*    Big Endian support added and Merged M0 and M3/M4 Source code.   
*    
* Version 1.0.3 2010/11/29   
*    Re-organized the CMSIS folders and updated documentation.    
*     
* Version 1.0.2 2010/11/11    
*    Documentation updated.     
*    
* Version 1.0.1 2010/10/05     
*    Production release and review comments incorporated.    
*    
* Version 1.0.0 2010/09/20     
*    Production release and review comments incorporated    
*    
* Version 0.0.7  2010/06/10     
*    Misra-C changes done    
* ------------------------------------------------------------------- */
#include "arm_math.h"


/**    
 * @addtogroup FIR_Sparse    
 * @{    
 */

/**   
 * @brief Processing function for the Q31 sparse FIR filter.   
 * @param[in]  *S          points to an instance of the Q31 sparse FIR structure.   
 * @param[in]  *pSrc       points to the block of input data.   
 * @param[out] *pDst       points to the block of output data   
 * @param[in]  *pScratchIn points to a temporary buffer of size blockSize.   
 * @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 32-bit accumulator.   
 * The 1.31 x 1.31 multiplications are truncated to 2.30 format.   
 * This leads to loss of precision on the intermediate multiplications and provides only a single guard bit.    
 * If the accumulator result overflows, it wraps around rather than saturate.   
 * In order to avoid overflows the input signal or coefficients must be scaled down by log2(numTaps) bits.   
 */

void arm_fir_sparse_q31(
  arm_fir_sparse_instance_q31 * S,
  q31_t * pSrc,
  q31_t * pDst,
  q31_t * pScratchIn,
  uint32_t blockSize)
{

  q31_t *pState = S->pState;                     /* State pointer */
  q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
  q31_t *px;                                     /* Scratch buffer pointer */
  q31_t *py = pState;                            /* Temporary pointers for state buffer */
  q31_t *pb = pScratchIn;                        /* Temporary pointers for scratch buffer */
  q31_t *pOut;                                   /* Destination pointer */
  q63_t out;                                     /* Temporary output variable */
  int32_t *pTapDelay = S->pTapDelay;             /* Pointer to the array containing offset of the non-zero tap values. */
  uint32_t delaySize = S->maxDelay + blockSize;  /* state length */
  uint16_t numTaps = S->numTaps;                 /* Filter order */
  int32_t readIndex;                             /* Read index of the state buffer */
  uint32_t tapCnt, blkCnt;                       /* loop counters */
  q31_t coeff = *pCoeffs++;                      /* Read the first coefficient value */
  q31_t in;


  /* BlockSize of Input samples are copied into the state buffer */
  /* StateIndex points to the starting position to write in the state buffer */
  arm_circularWrite_f32((int32_t *) py, delaySize, &S->stateIndex, 1,
                        (int32_t *) pSrc, 1, blockSize);

  /* Read Index, from where the state buffer should be read, is calculated. */
  readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;

  /* Wraparound of readIndex */
  if(readIndex < 0)
  {
    readIndex += (int32_t) delaySize;
  }

  /* Working pointer for state buffer is updated */
  py = pState;

  /* blockSize samples are read from the state buffer */
  arm_circularRead_f32((int32_t *) py, delaySize, &readIndex, 1,
                       (int32_t *) pb, (int32_t *) pb, blockSize, 1,
                       blockSize);

  /* Working pointer for the scratch buffer of state values */
  px = pb;

  /* Working pointer for scratch buffer of output values */
  pOut = pDst;


#ifndef ARM_MATH_CM0

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

  /* Loop over the blockSize. Unroll by a factor of 4.    
   * Compute 4 Multiplications at a time. */
  blkCnt = blockSize >> 2;

  while(blkCnt > 0u)
  {
    /* Perform Multiplications and store in the destination buffer */
    *pOut++ = (q31_t) (((q63_t) * px++ * coeff) >> 32);
    *pOut++ = (q31_t) (((q63_t) * px++ * coeff) >> 32);
    *pOut++ = (q31_t) (((q63_t) * px++ * coeff) >> 32);
    *pOut++ = (q31_t) (((q63_t) * px++ * coeff) >> 32);

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

  /* If the blockSize is not a multiple of 4,    
   * compute the remaining samples */
  blkCnt = blockSize % 0x4u;

  while(blkCnt > 0u)
  {
    /* Perform Multiplications and store in the destination buffer */
    *pOut++ = (q31_t) (((q63_t) * px++ * coeff) >> 32);

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

  /* Load the coefficient value and    
   * increment the coefficient buffer for the next set of state values */
  coeff = *pCoeffs++;

  /* Read Index, from where the state buffer should be read, is calculated. */
  readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;

  /* Wraparound of readIndex */
  if(readIndex < 0)
  {
    readIndex += (int32_t) delaySize;
  }

  /* Loop over the number of taps. */
  tapCnt = (uint32_t) numTaps - 1u;

  while(tapCnt > 0u)
  {
    /* Working pointer for state buffer is updated */
    py = pState;

    /* blockSize samples are read from the state buffer */
    arm_circularRead_f32((int32_t *) py, delaySize, &readIndex, 1,
                         (int32_t *) pb, (int32_t *) pb, blockSize, 1,
                         blockSize);

    /* Working pointer for the scratch buffer of state values */
    px = pb;

    /* Working pointer for scratch buffer of output values */
    pOut = pDst;

    /* Loop over the blockSize. Unroll by a factor of 4.    
     * Compute 4 MACS at a time. */
    blkCnt = blockSize >> 2;

    while(blkCnt > 0u)
    {
      out = *pOut;
      out += ((q63_t) * px++ * coeff) >> 32;
      *pOut++ = (q31_t) (out);

      out = *pOut;
      out += ((q63_t) * px++ * coeff) >> 32;
      *pOut++ = (q31_t) (out);

      out = *pOut;
      out += ((q63_t) * px++ * coeff) >> 32;
      *pOut++ = (q31_t) (out);

      out = *pOut;
      out += ((q63_t) * px++ * coeff) >> 32;
      *pOut++ = (q31_t) (out);

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

    /* If the blockSize is not a multiple of 4,    
     * compute the remaining samples */
    blkCnt = blockSize % 0x4u;

    while(blkCnt > 0u)
    {
      /* Perform Multiply-Accumulate */
      out = *pOut;
      out += ((q63_t) * px++ * coeff) >> 32;
      *pOut++ = (q31_t) (out);

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

    /* Load the coefficient value and    
     * increment the coefficient buffer for the next set of state values */
    coeff = *pCoeffs++;

    /* Read Index, from where the state buffer should be read, is calculated. */
    readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;

    /* Wraparound of readIndex */
    if(readIndex < 0)
    {
      readIndex += (int32_t) delaySize;
    }

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

  /* Working output pointer is updated */
  pOut = pDst;

  /* Output is converted into 1.31 format. */
  /* Loop over the blockSize. Unroll by a factor of 4.    
   * process 4 output samples at a time. */
  blkCnt = blockSize >> 2;

  while(blkCnt > 0u)
  {
    in = *pOut << 1;
    *pOut++ = in;
    in = *pOut << 1;
    *pOut++ = in;
    in = *pOut << 1;
    *pOut++ = in;
    in = *pOut << 1;
    *pOut++ = in;

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

  /* If the blockSize is not a multiple of 4,    
   * process the remaining output samples */
  blkCnt = blockSize % 0x4u;

  while(blkCnt > 0u)
  {
    in = *pOut << 1;
    *pOut++ = in;

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

#else

  /* Run the below code for Cortex-M0 */
  blkCnt = blockSize;

  while(blkCnt > 0u)
  {
    /* Perform Multiplications and store in the destination buffer */
    *pOut++ = (q31_t) (((q63_t) * px++ * coeff) >> 32);

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

  /* Load the coefficient value and           
   * increment the coefficient buffer for the next set of state values */
  coeff = *pCoeffs++;

  /* Read Index, from where the state buffer should be read, is calculated. */
  readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;

  /* Wraparound of readIndex */
  if(readIndex < 0)
  {
    readIndex += (int32_t) delaySize;
  }

  /* Loop over the number of taps. */
  tapCnt = (uint32_t) numTaps - 1u;

  while(tapCnt > 0u)
  {
    /* Working pointer for state buffer is updated */
    py = pState;

    /* blockSize samples are read from the state buffer */
    arm_circularRead_f32((int32_t *) py, delaySize, &readIndex, 1,
                         (int32_t *) pb, (int32_t *) pb, blockSize, 1,
                         blockSize);

    /* Working pointer for the scratch buffer of state values */
    px = pb;

    /* Working pointer for scratch buffer of output values */
    pOut = pDst;

    blkCnt = blockSize;

    while(blkCnt > 0u)
    {
      /* Perform Multiply-Accumulate */
      out = *pOut;
      out += ((q63_t) * px++ * coeff) >> 32;
      *pOut++ = (q31_t) (out);

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

    /* Load the coefficient value and           
     * increment the coefficient buffer for the next set of state values */
    coeff = *pCoeffs++;

    /* Read Index, from where the state buffer should be read, is calculated. */
    readIndex = (int32_t) (S->stateIndex - blockSize) - *pTapDelay++;

    /* Wraparound of readIndex */
    if(readIndex < 0)
    {
      readIndex += (int32_t) delaySize;
    }

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

  /* Working output pointer is updated */
  pOut = pDst;

  /* Output is converted into 1.31 format. */
  blkCnt = blockSize;

  while(blkCnt > 0u)
  {
    in = *pOut << 1;
    *pOut++ = in;

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

#endif /*   #ifndef ARM_MATH_CM0 */

}

/**    
 * @} end of FIR_Sparse group    
 */