text: /* ----------------------------------------------------------------------    
  * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
  *    
  * $Date:        19. March 2015
  * $Revision: 	V.1.4.5
  *    
  * Project: 	    CMSIS DSP Library    
  * Title:	    arm_fir_q31.c    
  *    
  * Description:	Q31 FIR filter processing function.    
  *    
  * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  *  
  * Redistribution and use in source and binary forms, with or without 
  * modification, are permitted provided that the following conditions
  * are met:
  *   - Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  *   - Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in
  *     the documentation and/or other materials provided with the 
  *     distribution.
  *   - Neither the name of ARM LIMITED nor the names of its contributors
  *     may be used to endorse or promote products derived from this
  *     software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.   
  * -------------------------------------------------------------------- */
  
  #include "arm_math.h"
  
  /**    
   * @ingroup groupFilters    
   */
  
  /**    
   * @addtogroup FIR    
   * @{    
   */
  
  /**    
   * @param[in] *S points to an instance of the Q31 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.    
   *    
   * @details    
   * <b>Scaling and Overflow Behavior:</b>    
   * \par    
   * The function is implemented using an internal 64-bit accumulator.    
   * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.    
   * Thus, if the accumulator result overflows it wraps around rather than clip.    
   * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.    
   * After all multiply-accumulates are performed, the 2.62 accumulator is right shifted by 31 bits and saturated to 1.31 format to yield the final result.  
   *    
   * \par    
   * Refer to the function <code>arm_fir_fast_q31()</code> for a faster but less precise implementation of this filter for Cortex-M3 and Cortex-M4.    
   */
  
  void arm_fir_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 */
  
  
  #ifndef ARM_MATH_CM0_FAMILY
  
    /* Run the below code for Cortex-M4 and Cortex-M3 */
  
    q31_t x0, x1, x2;                              /* 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;                        /* Accumulators */
    uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    uint32_t i, tapCnt, blkCnt, tapCntN3;          /* 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;
    blockSize = blockSize - (3 * blkCnt);
  
    tapCnt = numTaps / 3;
    tapCntN3 = numTaps - (3 * tapCnt);
  
    /* 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 three new input samples into the state buffer */
      *pStateCurnt++ = *pSrc++;
      *pStateCurnt++ = *pSrc++;
      *pStateCurnt++ = *pSrc++;
  
      /* Set all accumulators to zero */
      acc0 = 0;
      acc1 = 0;
      acc2 = 0;
  
      /* Initialize state pointer */
      px = pState;
  
      /* Initialize coefficient pointer */
      pb = pCoeffs;
  
      /* Read the first two samples from the state buffer:    
       *  x[n-numTaps], x[n-numTaps-1] */
      x0 = *(px++);
      x1 = *(px++);
  
      /* Loop unrolling.  Process 3 taps at a time. */
      i = tapCnt;
  
      while(i > 0u)
      {
        /* Read the b[numTaps] coefficient */
        c0 = *pb;
  
        /* Read x[n-numTaps-2] sample */
        x2 = *(px++);
  
        /* Perform the multiply-accumulates */
        acc0 += ((q63_t) x0 * c0);
        acc1 += ((q63_t) x1 * c0);
        acc2 += ((q63_t) x2 * c0);
  
        /* Read the coefficient and state */
        c0 = *(pb + 1u);
        x0 = *(px++);
  
        /* Perform the multiply-accumulates */
        acc0 += ((q63_t) x1 * c0);
        acc1 += ((q63_t) x2 * c0);
        acc2 += ((q63_t) x0 * c0);
  
        /* Read the coefficient and state */
        c0 = *(pb + 2u);
        x1 = *(px++);
  
        /* update coefficient pointer */
        pb += 3u;
  
        /* Perform the multiply-accumulates */
        acc0 += ((q63_t) x2 * c0);
        acc1 += ((q63_t) x0 * c0);
        acc2 += ((q63_t) x1 * c0);
  
        /* Decrement the loop counter */
        i--;
      }
  
      /* If the filter length is not a multiple of 3, compute the remaining filter taps */
  
      i = tapCntN3;
  
      while(i > 0u)
      {
        /* Read coefficients */
        c0 = *(pb++);
  
        /* Fetch 1 state variable */
        x2 = *(px++);
  
        /* Perform the multiply-accumulates */
        acc0 += ((q63_t) x0 * c0);
        acc1 += ((q63_t) x1 * c0);
        acc2 += ((q63_t) x2 * c0);
  
        /* Reuse the present sample states for next sample */
        x0 = x1;
        x1 = x2;
  
        /* Decrement the loop counter */
        i--;
      }
  
      /* Advance the state pointer by 3 to process the next group of 3 samples */
      pState = pState + 3;
  
      /* The results in the 3 accumulators are in 2.30 format.  Convert to 1.31    
       ** Then store the 3 outputs in the destination buffer. */
      *pDst++ = (q31_t) (acc0 >> 31u);
      *pDst++ = (q31_t) (acc1 >> 31u);
      *pDst++ = (q31_t) (acc2 >> 31u);
  
      /* Decrement the samples loop counter */
      blkCnt--;
    }
  
    /* If the blockSize is not a multiple of 3, compute any remaining output samples here.    
     ** No loop unrolling is used. */
  
    while(blockSize > 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 += (q63_t) * (px++) * (*(pb++));
        i--;
      } while(i > 0u);
  
      /* The result is in 2.62 format.  Convert to 1.31    
       ** Then store the output in the destination buffer. */
      *pDst++ = (q31_t) (acc0 >> 31u);
  
      /* Advance state pointer by 1 for the next sample */
      pState = pState + 1;
  
      /* Decrement the samples loop counter */
      blockSize--;
    }
  
    /* 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
  
  /* Run the below code for Cortex-M0 */
  
    q31_t *px;                                     /* Temporary pointer for state */
    q31_t *pb;                                     /* Temporary pointer for coefficient buffer */
    q63_t acc;                                     /* Accumulator */
    uint32_t numTaps = S->numTaps;                 /* Length of the filter */
    uint32_t i, tapCnt, blkCnt;                    /* Loop counters */
  
    /* S->pState buffer 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;
  
      /* 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 += (q63_t) * px++ * *pb++;
        i--;
      } while(i > 0u);
  
      /* The result is in 2.62 format.  Convert to 1.31         
       ** Then store the output in the destination buffer. */
      *pDst++ = (q31_t) (acc >> 31u);
  
      /* 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 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 the data */
    while(tapCnt > 0u)
    {
      *pStateCurnt++ = *pState++;
  
      /* Decrement the loop counter */
      tapCnt--;
    }
  
  
  #endif /*  #ifndef ARM_MATH_CM0_FAMILY */
  
  }
  
  /**    
   * @} end of FIR group    
   */
  