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_f32.c  
*  
* Description:    Floating-point 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 1.0.2 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 0.0.5  2010/04/26   
*      incorporated review comments and updated with latest CMSIS layer  
*  
* Version 0.0.3  2010/03/10   
*    Initial version  
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**  
 * @ingroup groupFilters  
 */

/**  
 * @defgroup FIR Finite Impulse Response (FIR) Filters  
 *  
 * This set of functions implements Finite Impulse Response (FIR) filters  
 * for Q7, Q15, Q31, and floating-point data types.  Fast versions of Q15 and Q31 are also provided.  
 * 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> points to input and output arrays containing <code>blockSize</code> values.  
 *  
 * \par Algorithm:  
 * The FIR filter algorithm is based upon a sequence of multiply-accumulate (MAC) operations.  
 * Each filter coefficient <code>b[n]</code> is multiplied by a state variable which equals a previous input sample <code>x[n]</code>.  
 * <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>  
 * \par  
 * \image html FIR.gif "Finite Impulse Response filter"  
 * \par  
 * <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 following 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>  
 * \par  
 * Note that the length of the state buffer exceeds the length of the coefficient array by <code>blockSize-1</code>.  
 * The increased state buffer length allows circular addressing, which is traditionally used in the FIR filters,  
 * to be avoided and yields a significant speed improvement.  
 * 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 4 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.  
 *  
 * \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 before static initialization.  
 * The code below statically initializes each of the 4 different data type filter instance structures  
 * <pre>  
 *arm_fir_instance_f32 S = {numTaps, pState, pCoeffs};  
 *arm_fir_instance_q31 S = {numTaps, pState, pCoeffs};  
 *arm_fir_instance_q15 S = {numTaps, pState, pCoeffs};  
 *arm_fir_instance_q7 S =  {numTaps, pState, pCoeffs};  
 * </pre>  
 *  
 * where <code>numTaps</code> is the number of filter coefficients 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 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  
 * @{  
 */

/**  
 *  
 * @param[in]  *S points to an instance of the floating-point FIR filter 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 per call.  
 * @return     none.  
 *  
 */

#ifndef ARM_MATH_CM0

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

void arm_fir_f32(
  const arm_fir_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 acc0, acc1, acc2, acc3, acc4, acc5, acc6, acc7;     /* Accumulators */
  float32_t x0, x1, x2, x3, x4, x5, x6, x7, 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;                    /* Loop counters */

  /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
  /* pStateCurnt points to the location where the new input data should be written */
  pStateCurnt = &(S->pState[(numTaps - 1u)]);

  /* Apply loop unrolling and compute 4 output values simultaneously.  
   * The variables acc0 ... acc3 hold output values that are being computed:  
   *  
   *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]  
   *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]  
   *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]  
   *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]  
   */
  blkCnt = blockSize >> 3;

  /* 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)
  {
    /* Copy four new input samples into the state buffer */
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;
    *pStateCurnt++ = *pSrc++;

    /* Set all accumulators to zero */
    acc0 = 0.0f;
    acc1 = 0.0f;
    acc2 = 0.0f;
    acc3 = 0.0f;
    acc4 = 0.0f;
    acc5 = 0.0f;
    acc6 = 0.0f;
    acc7 = 0.0f;

    /* Initialize state pointer */
    px = pState;

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

    /* Read the first three samples from the state buffer:  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
    x0 = *px++;
    x1 = *px++;
    x2 = *px++;
    x3 = *px++;
    x4 = *px++;
    x5 = *px++;
    x6 = *px++;

    /* Loop unrolling.  Process 4 taps at a time. */
    tapCnt = numTaps >> 3u;

    /* 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-3] sample */
      x7 = *(px++);

      /* acc0 +=  b[numTaps-1] * x[n-numTaps] */
      acc0 += x0 * c0;

      /* acc1 +=  b[numTaps-1] * x[n-numTaps-1] */
      acc1 += x1 * c0;

      /* acc2 +=  b[numTaps-1] * x[n-numTaps-2] */
      acc2 += x2 * c0;

      /* acc3 +=  b[numTaps-1] * x[n-numTaps-3] */
      acc3 += x3 * c0;

      /* acc4 +=  b[numTaps-1] * x[n-numTaps-4] */
      acc4 += x4 * c0;

      /* acc1 +=  b[numTaps-1] * x[n-numTaps-5] */
      acc5 += x5 * c0;

      /* acc2 +=  b[numTaps-1] * x[n-numTaps-6] */
      acc6 += x6 * c0;

      /* acc3 +=  b[numTaps-1] * x[n-numTaps-7] */
      acc7 += x7 * c0;

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

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

      /* Perform the multiply-accumulate */
      acc0 += x1 * c0;
      acc1 += x2 * c0;
      acc2 += x3 * c0;
      acc3 += x4 * c0;
      acc4 += x5 * c0;
      acc5 += x6 * c0;
      acc6 += x7 * c0;
      acc7 += x0 * c0;

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

      /* Read x[n-numTaps-5] sample */
      x1 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x2 * c0;
      acc1 += x3 * c0;
      acc2 += x4 * c0;
      acc3 += x5 * c0;
      acc4 += x6 * c0;
      acc5 += x7 * c0;
      acc6 += x0 * c0;
      acc7 += x1 * c0;

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

      /* Read x[n-numTaps-6] sample */
      x2 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x3 * c0;
      acc1 += x4 * c0;
      acc2 += x5 * c0;
      acc3 += x6 * c0;
      acc4 += x7 * c0;
      acc5 += x0 * c0;
      acc6 += x1 * c0;
      acc7 += x2 * c0;

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

      /* Read x[n-numTaps-6] sample */
      x3 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x4 * c0;
      acc1 += x5 * c0;
      acc2 += x6 * c0;
      acc3 += x7 * c0;
      acc4 += x0 * c0;
      acc5 += x1 * c0;
      acc6 += x2 * c0;
      acc7 += x3 * c0;

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

      /* Read x[n-numTaps-6] sample */
      x4 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x5 * c0;
      acc1 += x6 * c0;
      acc2 += x7 * c0;
      acc3 += x0 * c0;
      acc4 += x1 * c0;
      acc5 += x2 * c0;
      acc6 += x3 * c0;
      acc7 += x4 * c0;

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

      /* Read x[n-numTaps-6] sample */
      x5 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x6 * c0;
      acc1 += x7 * c0;
      acc2 += x0 * c0;
      acc3 += x1 * c0;
      acc4 += x2 * c0;
      acc5 += x3 * c0;
      acc6 += x4 * c0;
      acc7 += x5 * c0;

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

      /* Read x[n-numTaps-6] sample */
      x6 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x7 * c0;
      acc1 += x0 * c0;
      acc2 += x1 * c0;
      acc3 += x2 * c0;
      acc4 += x3 * c0;
      acc5 += x4 * c0;
      acc6 += x5 * c0;
      acc7 += x6 * c0;

      tapCnt--;
    }

    /* If the filter length is not a multiple of 4, compute the remaining filter taps */
    tapCnt = numTaps % 0x8u;

    while(tapCnt > 0u)
    {
      /* Read coefficients */
      c0 = *(pb++);

      /* Fetch 1 state variable */
      x7 = *(px++);

      /* Perform the multiply-accumulates */
      acc0 += x0 * c0;
      acc1 += x1 * c0;
      acc2 += x2 * c0;
      acc3 += x3 * c0;
      acc4 += x4 * c0;
      acc5 += x5 * c0;
      acc6 += x6 * c0;
      acc7 += x7 * c0;

      /* Reuse the present sample states for next sample */
      x0 = x1;
      x1 = x2;
      x2 = x3;
      x3 = x4;
      x4 = x5;
      x5 = x6;
      x6 = x7;

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

    /* Advance the state pointer by 4 to process the next group of 4 samples */
    pState = pState + 8;

    /* The results in the 4 accumulators, store in the destination buffer. */
    *pDst++ = acc0;
    *pDst++ = acc1;
    *pDst++ = acc2;
    *pDst++ = acc3;
    *pDst++ = acc4;
    *pDst++ = acc5;
    *pDst++ = acc6;
    *pDst++ = acc7;

    blkCnt--;
  }

  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
   ** No loop unrolling is used. */
  blkCnt = blockSize % 0x8u;

  while(blkCnt > 0u)
  {
    /* Copy one sample at a time into state buffer */
    *pStateCurnt++ = *pSrc++;

    /* Set the accumulator to zero */
    acc0 = 0.0f;

    /* Initialize state pointer */
    px = pState;

    /* Initialize Coefficient pointer */
    pb = (pCoeffs);

    i = numTaps;

    /* Perform the multiply-accumulates */
    do
    {
      acc0 += *px++ * *pb++;
      i--;

    } while(i > 0u);

    /* The result is store in the destination buffer. */
    *pDst++ = acc0;

    /* Advance state pointer by 1 for the next sample */
    pState = pState + 1;

    blkCnt--;
  }

  /* 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;

  tapCnt = (numTaps - 1u) >> 2u;

  /* copy data */
  while(tapCnt > 0u)
  {
    *pStateCurnt++ = *pState++;
    *pStateCurnt++ = *pState++;
    *pStateCurnt++ = *pState++;
    *pStateCurnt++ = *pState++;

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

  /* Calculate remaining number of copies */
  tapCnt = (numTaps - 1u) % 0x4u;

  /* Copy the remaining q31_t data */
  while(tapCnt > 0u)
  {
    *pStateCurnt++ = *pState++;

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

#else

void arm_fir_f32(
  const arm_fir_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 */
  uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
  uint32_t i, tapCnt, blkCnt;                    /* Loop counters */

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

  float32_t acc;

  /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
  /* pStateCurnt points to the location where the new input data should be written */
  pStateCurnt = &(S->pState[(numTaps - 1u)]);

  /* Initialize blkCnt with blockSize */
  blkCnt = blockSize;

  while(blkCnt > 0u)
  {
    /* Copy one sample at a time into state buffer */
    *pStateCurnt++ = *pSrc++;

    /* Set the accumulator to zero */
    acc = 0.0f;

    /* Initialize state pointer */
    px = pState;

    /* Initialize Coefficient pointer */
    pb = pCoeffs;

    i = numTaps;

    /* Perform the multiply-accumulates */
    do
    {
      /* acc =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] */
      acc += *px++ * *pb++;
      i--;

    } while(i > 0u);

    /* The result is store in the destination buffer. */
    *pDst++ = acc;

    /* Advance state pointer by 1 for the next sample */
    pState = pState + 1;

    blkCnt--;
  }

  /* Processing is complete.         
   ** Now copy the last numTaps - 1 samples to the starting 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 */
  tapCnt = numTaps - 1u;

  /* Copy data */
  while(tapCnt > 0u)
  {
    *pStateCurnt++ = *pState++;

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

}

#endif /*   #ifndef ARM_MATH_CM0 */

/**  
 * @} end of FIR group  
 */