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_q15.c  
*  
* Description:  Q15 Fast 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 0.0.9  2010/08/16   
*    Initial version  
*  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @addtogroup FIR  
 * @{  
 */ 
 
/**  
 * @param[in] *S points to an instance of the Q15 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.  
 *  
 * <b>Scaling and Overflow Behavior:</b>  
 * \par  
 * This fast version uses a 32-bit accumulator with 2.30 format.  
 * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.  
 * Thus, if the accumulator result overflows it wraps around and distorts the result.  
 * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.  
 * The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result.  
 *  
 * \par  
 * Refer to the function <code>arm_fir_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion.  Both the slow and the fast versions use the same instance structure.  
 * Use the function <code>arm_fir_init_q15()</code> to initialize the filter structure.  
 */ 
 
void arm_fir_fast_q15( 
  const arm_fir_instance_q15 * S, 
  q15_t * pSrc, 
  q15_t * pDst, 
  uint32_t blockSize) 
{ 
  q15_t *pState = S->pState;                     /* State pointer */ 
  q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */ 
  q15_t *pStateCurnt;                            /* Points to the current sample of the state */ 
  q15_t *px1;                                    /* Temporary q15 pointer for state buffer */ 
  q31_t *pb;                                     /* Temporary pointer for coefficient buffer */ 
  q31_t *px2;                                    /* Temporary q31 pointer for SIMD state buffer accesses */ 
  q31_t x0, x1, x2, x3, c0;                      /* Temporary variables to hold SIMD state and coefficient values */ 
  q31_t acc0, acc1, acc2, acc3;                  /* Accumulators */ 
  uint32_t numTaps = S->numTaps;                 /* Number of taps in the filter */ 
  uint32_t 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.  
     ** Use 32-bit SIMD to move the 16-bit data.  Only requires two copies. */ 
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; 
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; 
 
    /* Set all accumulators to zero */ 
    acc0 = 0; 
    acc1 = 0; 
    acc2 = 0; 
    acc3 = 0; 
 
    /* Initialize state pointer of type q15 */ 
    px1 = pState; 
 
    /* Initialize coeff pointer of type q31 */ 
    pb = (q31_t *) (pCoeffs); 
 
    /* Read the first two samples from the state buffer:  x[n-N], x[n-N-1] */ 
    x0 = *(q31_t *) (px1++); 
 
    /* Read the third and forth samples from the state buffer: x[n-N-1], x[n-N-2] */ 
    x1 = *(q31_t *) (px1++); 
 
    /* Loop over the number of taps.  Unroll by a factor of 4.  
     ** Repeat until we've computed numTaps-4 coefficients. */ 
    tapCnt = numTaps >> 2; 
    do 
    { 
      /* Read the first two coefficients using SIMD:  b[N] and b[N-1] coefficients */ 
      c0 = *(pb++); 
 
      /* acc0 +=  b[N] * x[n-N] + b[N-1] * x[n-N-1] */ 
      acc0 = __SMLAD(x0, c0, acc0); 
 
      /* acc1 +=  b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */ 
      acc1 = __SMLAD(x1, c0, acc1); 
 
      /* Read state x[n-N-2], x[n-N-3] */ 
      x2 = *(q31_t *) (px1++); 
 
      /* Read state x[n-N-3], x[n-N-4] */ 
      x3 = *(q31_t *) (px1++); 
 
      /* acc2 +=  b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */ 
      acc2 = __SMLAD(x2, c0, acc2); 
 
      /* acc3 +=  b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */ 
      acc3 = __SMLAD(x3, c0, acc3); 
 
      /* Read coefficients b[N-2], b[N-3] */ 
      c0 = *(pb++); 
 
      /* acc0 +=  b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */ 
      acc0 = __SMLAD(x2, c0, acc0); 
 
      /* acc1 +=  b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */ 
      acc1 = __SMLAD(x3, c0, acc1); 
 
      /* Read state x[n-N-4], x[n-N-5] */ 
      x0 = *(q31_t *) (px1++); 
 
      /* Read state x[n-N-5], x[n-N-6] */ 
      x1 = *(q31_t *) (px1++); 
 
      /* acc2 +=  b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */ 
      acc2 = __SMLAD(x0, c0, acc2); 
 
      /* acc3 +=  b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */ 
      acc3 = __SMLAD(x1, c0, acc3); 
      tapCnt--; 
 
    } 
    while(tapCnt > 0u); 
 
    /* If the filter length is not a multiple of 4, compute the remaining filter taps.  
     ** This is always 2 taps since the filter length is always even. */ 
    if((numTaps & 0x3u) != 0u) 
    { 
      /* Read 2 coefficients */ 
      c0 = *(pb++); 
      /* Fetch 4 state variables */ 
      x2 = *(q31_t *) (px1++); 
      x3 = *(q31_t *) (px1++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 = __SMLAD(x0, c0, acc0); 
      acc1 = __SMLAD(x1, c0, acc1); 
      acc2 = __SMLAD(x2, c0, acc2); 
      acc3 = __SMLAD(x3, c0, acc3); 
    } 
 
    /* The results in the 4 accumulators are in 2.30 format.  Convert to 1.15 with saturation.  
     ** Then store the 4 outputs in the destination buffer. */ 
    *__SIMD32(pDst)++ = __PKHBT((acc0 >> 15), (acc1 >> 15), 16u); 
    *__SIMD32(pDst)++ = __PKHBT((acc2 >> 15), (acc3 >> 15), 16u); 
 
 
    /* Advance the state pointer by 4 to process the next group of 4 samples */ 
    pState = pState + 4; 
 
    /* Decrement the 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 % 0x4u; 
  while(blkCnt > 0u) 
  { 
    /* Copy two samples into state buffer */ 
    *pStateCurnt++ = *pSrc++; 
 
    /* Set the accumulator to zero */ 
    acc0 = 0; 
 
    /* Use SIMD to hold states and coefficients */ 
    px2 = (q31_t *) pState; 
    pb = (q31_t *) (pCoeffs); 
    tapCnt = numTaps >> 1; 
 
    do 
    { 
      acc0 = __SMLAD(*px2++, *(pb++), acc0); 
      tapCnt--; 
    } 
    while(tapCnt > 0u); 
 
    /* The result is in 2.30 format.  Convert to 1.15 with saturation.  
     ** Then store the output in the destination buffer. */ 
    *pDst++ = (q15_t) ((acc0 >> 15)); 
 
    /* Advance state pointer by 1 for the next sample */ 
    pState = pState + 1; 
 
    /* Decrement the 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; 
  /* Calculation of count for copying integer writes */ 
  tapCnt = (numTaps - 1u) >> 2; 
 
  while(tapCnt > 0u) 
  { 
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; 
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; 
 
    tapCnt--; 
  } 
 
  /* Calculation of count for remaining q15_t data */ 
  tapCnt = (numTaps - 1u) % 0x4u; 
 
  /* copy remaining data */ 
  while(tapCnt > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    tapCnt--; 
  } 
} 
 
/**  
 * @} end of FIR group  
 */