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_fast_q31.c  
*  
* Description:	Processing function for the Q31 Fast FIR filter.  
*  
* 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 0.0.9  2010/08/27   
*    Initial version  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @addtogroup FIR  
 * @{  
 */ 
 
/**  
 * @param[in] *S points to an instance of the Q31 structure.  
 * @param[in] *pSrc points to the block of input data.  
 * @param[out] *pDst points to the block output data.  
 * @param[in] blockSize number of samples to process per call.  
 * @return none.  
 *  
 * <b>Scaling and Overflow Behavior:</b>  
 *  
 * \par  
 * This function is optimized for speed at the expense of fixed-point precision and overflow protection.  
 * The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format.  
 * These intermediate results are added to a 2.30 accumulator.  
 * Finally, the accumulator is saturated and converted to a 1.31 result.  
 * The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result.  
 * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.  
 *  
 * \par  
 * Refer to the function <code>arm_fir_q31()</code> for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision.  Both the slow and the fast versions use the same instance structure.  
 * Use the function <code>arm_fir_init_q31()</code> to initialize the filter structure.  
 */ 
 
void arm_fir_fast_q31( 
  const arm_fir_instance_q31 * S, 
  q31_t * pSrc, 
  q31_t * pDst, 
  uint32_t blockSize) 
{ 
  q31_t *pState = S->pState;                     /* State pointer */ 
  q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */ 
  q31_t *pStateCurnt;                            /* Points to the current sample of the state */ 
  q31_t x0, x1, x2, x3;                          /* Temporary variables to hold state */ 
  q31_t c0;                                      /* Temporary variable to hold coefficient value */ 
  q31_t *px;                                     /* Temporary pointer for state */ 
  q31_t *pb;                                     /* Temporary pointer for coefficient buffer */ 
  q63_t acc0, acc1, acc2, acc3;                  /* Accumulators */ 
  uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */ 
  uint32_t i, tapCnt, blkCnt;                    /* Loop counters */ 
 
  /* S->pState points to buffer 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 >> 2; 
 
  /* 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++; 
 
    /* Set all accumulators to zero */ 
    acc0 = 0; 
    acc1 = 0; 
    acc2 = 0; 
    acc3 = 0; 
 
    /* Initialize state pointer */ 
    px = pState; 
 
    /* Initialize coefficient 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++); 
 
    /* Loop unrolling.  Process 4 taps at a time. */ 
    tapCnt = numTaps >> 2; 
    i = tapCnt; 
 
    while(i > 0u) 
    { 
      /* Read the b[numTaps] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-3] sample */ 
      x3 = *(px++); 
 
      /* acc0 +=  b[numTaps] * x[n-numTaps] */ 
      acc0 = (q31_t) ((((q63_t) x0 * c0) + (acc0 << 32)) >> 32); 
 
      /* acc1 +=  b[numTaps] * x[n-numTaps-1] */ 
      acc1 = (q31_t) ((((q63_t) x1 * c0) + (acc1 << 32)) >> 32); 
 
      /* acc2 +=  b[numTaps] * x[n-numTaps-2] */ 
      acc2 = (q31_t) ((((q63_t) x2 * c0) + (acc2 << 32)) >> 32); 
 
      /* acc3 +=  b[numTaps] * x[n-numTaps-3] */ 
      acc3 = (q31_t) ((((q63_t) x3 * c0) + (acc3 << 32)) >> 32); 
 
      /* Read the b[numTaps-1] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-4] sample */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 = (q31_t) ((((q63_t) x1 * c0) + (acc0 << 32)) >> 32); 
      acc1 = (q31_t) ((((q63_t) x2 * c0) + (acc1 << 32)) >> 32); 
      acc2 = (q31_t) ((((q63_t) x3 * c0) + (acc2 << 32)) >> 32); 
      acc3 = (q31_t) ((((q63_t) x0 * c0) + (acc3 << 32)) >> 32); 
 
      /* Read the b[numTaps-2] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-5] sample */ 
      x1 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 = (q31_t) ((((q63_t) x2 * c0) + (acc0 << 32)) >> 32); 
      acc1 = (q31_t) ((((q63_t) x3 * c0) + (acc1 << 32)) >> 32); 
      acc2 = (q31_t) ((((q63_t) x0 * c0) + (acc2 << 32)) >> 32); 
      acc3 = (q31_t) ((((q63_t) x1 * c0) + (acc3 << 32)) >> 32); 
 
      /* Read the b[numTaps-3] coefficients */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-6] sample */ 
      x2 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 = (q31_t) ((((q63_t) x3 * c0) + (acc0 << 32)) >> 32); 
      acc1 = (q31_t) ((((q63_t) x0 * c0) + (acc1 << 32)) >> 32); 
      acc2 = (q31_t) ((((q63_t) x1 * c0) + (acc2 << 32)) >> 32); 
      acc3 = (q31_t) ((((q63_t) x2 * c0) + (acc3 << 32)) >> 32); 
      i--; 
    } 
 
    /* If the filter length is not a multiple of 4, compute the remaining filter taps */ 
 
    i = numTaps - (tapCnt * 4u); 
    while(i > 0u) 
    { 
      /* Read coefficients */ 
      c0 = *(pb++); 
 
      /* Fetch 1 state variable */ 
      x3 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 = (q31_t) ((((q63_t) x0 * c0) + (acc0 << 32)) >> 32); 
      acc1 = (q31_t) ((((q63_t) x1 * c0) + (acc1 << 32)) >> 32); 
      acc2 = (q31_t) ((((q63_t) x2 * c0) + (acc2 << 32)) >> 32); 
      acc3 = (q31_t) ((((q63_t) x3 * c0) + (acc3 << 32)) >> 32); 
 
      /* Reuse the present sample states for next sample */ 
      x0 = x1; 
      x1 = x2; 
      x2 = x3; 
 
      /* Decrement the loop counter */ 
      i--; 
    } 
 
    /* Advance the state pointer by 4 to process the next group of 4 samples */ 
    pState = pState + 4; 
 
    /* The results in the 4 accumulators are in 2.30 format.  Convert to 1.31  
     ** Then store the 4 outputs in the destination buffer. */ 
    *pDst++ = (q31_t) (acc0 << 1); 
    *pDst++ = (q31_t) (acc1 << 1); 
    *pDst++ = (q31_t) (acc2 << 1); 
    *pDst++ = (q31_t) (acc3 << 1); 
 
    /* Decrement the samples loop counter */ 
    blkCnt--; 
  } 
 
 
  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
   ** No loop unrolling is used. */ 
  blkCnt = blockSize % 4u; 
 
  while(blkCnt > 0u) 
  { 
    /* Copy one sample at a time into state buffer */ 
    *pStateCurnt++ = *pSrc++; 
 
    /* Set the accumulator to zero */ 
    acc0 = 0; 
 
    /* Initialize state pointer */ 
    px = pState; 
 
    /* Initialize Coefficient pointer */ 
    pb = (pCoeffs); 
 
    i = numTaps; 
 
    /* Perform the multiply-accumulates */ 
    do 
    { 
      acc0 = (q31_t) ((((q63_t) * (px++) * (*(pb++))) + (acc0 << 32)) >> 32); 
      i--; 
    } while(i > 0u); 
 
    /* The result is in 2.30 format.  Convert to 1.31  
     ** Then store the output in the destination buffer. */ 
    *pDst++ = (q31_t) (acc0 << 1); 
 
    /* Advance state pointer by 1 for the next sample */ 
    pState = pState + 1; 
 
    /* Decrement the samples loop counter */ 
    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--; 
  } 
 
} 
 
/**  
 * @} end of FIR group  
 */