File content as of revision 0:1014af42efd9:

/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:	    arm_fir_sparse_q31.c  
*  
* Description:	Q31 sparse FIR filter processing function. 
*  
* Target Processor: Cortex-M4/Cortex-M3
*  
* 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; 
 
  /* 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 1.15 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--; 
  } 
} 
 
/**  
 * @} end of FIR_Sparse group  
 */