text: /* ----------------------------------------------------------------------    
  * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
  *    
  * $Date: 16/10/14 6:01p $Revision: 	V.1.4.5
  *    
  * Project: 	    CMSIS DSP Library    
  * Title:	    arm_fir_lattice_q31.c    
  *    
  * Description:	Q31 FIR lattice 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_Lattice    
   * @{    
   */
  
  
  /**    
   * @brief Processing function for the Q31 FIR lattice filter.    
   * @param[in]  *S        points to an instance of the Q31 FIR lattice 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.    
   * @return none.    
   *    
   * @details    
   * <b>Scaling and Overflow Behavior:</b>    
   * In order to avoid overflows the input signal must be scaled down by 2*log2(numStages) bits.    
   */
  
  #ifndef ARM_MATH_CM0_FAMILY
  
    /* Run the below code for Cortex-M4 and Cortex-M3 */
  
  void arm_fir_lattice_q31(
    const arm_fir_lattice_instance_q31 * S,
    q31_t * pSrc,
    q31_t * pDst,
    uint32_t blockSize)
  {
    q31_t *pState;                                 /* State pointer */
    q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    q31_t *px;                                     /* temporary state pointer */
    q31_t *pk;                                     /* temporary coefficient pointer */
    q31_t fcurr1, fnext1, gcurr1 = 0, gnext1;      /* temporary variables for first sample in loop unrolling */
    q31_t fcurr2, fnext2, gnext2;                  /* temporary variables for second sample in loop unrolling */
    uint32_t numStages = S->numStages;             /* Length of the filter */
    uint32_t blkCnt, stageCnt;                     /* temporary variables for counts */
    q31_t k;
  
    pState = &S->pState[0];
  
    blkCnt = blockSize >> 1u;
  
    /* First part of the processing with loop unrolling.  Compute 2 outputs at a time.        
       a second loop below computes the remaining 1 sample. */
    while(blkCnt > 0u)
    {
      /* f0(n) = x(n) */
      fcurr1 = *pSrc++;
  
      /* f0(n) = x(n) */
      fcurr2 = *pSrc++;
  
      /* Initialize coeff pointer */
      pk = (pCoeffs);
  
      /* Initialize state pointer */
      px = pState;
  
      /* read g0(n - 1) from state buffer */
      gcurr1 = *px;
  
      /* Read the reflection coefficient */
      k = *pk++;
  
      /* for sample 1 processing */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext1 = (q31_t) (((q63_t) gcurr1 * k) >> 32);
  
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext1 = (q31_t) (((q63_t) fcurr1 * (k)) >> 32);
      fnext1 = fcurr1 + (fnext1 << 1u);
      gnext1 = gcurr1 + (gnext1 << 1u);
  
      /* for sample 1 processing */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext2 = (q31_t) (((q63_t) fcurr1 * k) >> 32);
  
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext2 = (q31_t) (((q63_t) fcurr2 * (k)) >> 32);
      fnext2 = fcurr2 + (fnext2 << 1u);
      gnext2 = fcurr1 + (gnext2 << 1u);
  
      /* save g1(n) in state buffer */
      *px++ = fcurr2;
  
      /* f1(n) is saved in fcurr1        
         for next stage processing */
      fcurr1 = fnext1;
      fcurr2 = fnext2;
  
      stageCnt = (numStages - 1u);
  
      /* stage loop */
      while(stageCnt > 0u)
      {
  
        /* Read the reflection coefficient */
        k = *pk++;
  
        /* read g2(n) from state buffer */
        gcurr1 = *px;
  
        /* save g1(n) in state buffer */
        *px++ = gnext2;
  
        /* Sample processing for K2, K3.... */
        /* f2(n) = f1(n) +  K2 * g1(n-1) */
        fnext1 = (q31_t) (((q63_t) gcurr1 * k) >> 32);
        fnext2 = (q31_t) (((q63_t) gnext1 * k) >> 32);
  
        fnext1 = fcurr1 + (fnext1 << 1u);
        fnext2 = fcurr2 + (fnext2 << 1u);
  
        /* g2(n) = f1(n) * K2  +  g1(n-1) */
        gnext2 = (q31_t) (((q63_t) fcurr2 * (k)) >> 32);
        gnext2 = gnext1 + (gnext2 << 1u);
  
        /* g2(n) = f1(n) * K2  +  g1(n-1) */
        gnext1 = (q31_t) (((q63_t) fcurr1 * (k)) >> 32);
        gnext1 = gcurr1 + (gnext1 << 1u);
  
        /* f1(n) is saved in fcurr1        
           for next stage processing */
        fcurr1 = fnext1;
        fcurr2 = fnext2;
  
        stageCnt--;
  
      }
  
      /* y(n) = fN(n) */
      *pDst++ = fcurr1;
      *pDst++ = fcurr2;
  
      blkCnt--;
  
    }
  
    /* If the blockSize is not a multiple of 4, compute any remaining output samples here.        
     ** No loop unrolling is used. */
    blkCnt = blockSize % 0x2u;
  
    while(blkCnt > 0u)
    {
      /* f0(n) = x(n) */
      fcurr1 = *pSrc++;
  
      /* Initialize coeff pointer */
      pk = (pCoeffs);
  
      /* Initialize state pointer */
      px = pState;
  
      /* read g0(n - 1) from state buffer */
      gcurr1 = *px;
  
      /* Read the reflection coefficient */
      k = *pk++;
  
      /* for sample 1 processing */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext1 = (q31_t) (((q63_t) gcurr1 * k) >> 32);
      fnext1 = fcurr1 + (fnext1 << 1u);
  
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext1 = (q31_t) (((q63_t) fcurr1 * (k)) >> 32);
      gnext1 = gcurr1 + (gnext1 << 1u);
  
      /* save g1(n) in state buffer */
      *px++ = fcurr1;
  
      /* f1(n) is saved in fcurr1        
         for next stage processing */
      fcurr1 = fnext1;
  
      stageCnt = (numStages - 1u);
  
      /* stage loop */
      while(stageCnt > 0u)
      {
        /* Read the reflection coefficient */
        k = *pk++;
  
        /* read g2(n) from state buffer */
        gcurr1 = *px;
  
        /* save g1(n) in state buffer */
        *px++ = gnext1;
  
        /* Sample processing for K2, K3.... */
        /* f2(n) = f1(n) +  K2 * g1(n-1) */
        fnext1 = (q31_t) (((q63_t) gcurr1 * k) >> 32);
        fnext1 = fcurr1 + (fnext1 << 1u);
  
        /* g2(n) = f1(n) * K2  +  g1(n-1) */
        gnext1 = (q31_t) (((q63_t) fcurr1 * (k)) >> 32);
        gnext1 = gcurr1 + (gnext1 << 1u);
  
        /* f1(n) is saved in fcurr1        
           for next stage processing */
        fcurr1 = fnext1;
  
        stageCnt--;
  
      }
  
  
      /* y(n) = fN(n) */
      *pDst++ = fcurr1;
  
      blkCnt--;
  
    }
  
  
  }
  
  
  #else
  
  /* Run the below code for Cortex-M0 */
  
  void arm_fir_lattice_q31(
    const arm_fir_lattice_instance_q31 * S,
    q31_t * pSrc,
    q31_t * pDst,
    uint32_t blockSize)
  {
    q31_t *pState;                                 /* State pointer */
    q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    q31_t *px;                                     /* temporary state pointer */
    q31_t *pk;                                     /* temporary coefficient pointer */
    q31_t fcurr, fnext, gcurr, gnext;              /* temporary variables */
    uint32_t numStages = S->numStages;             /* Length of the filter */
    uint32_t blkCnt, stageCnt;                     /* temporary variables for counts */
  
    pState = &S->pState[0];
  
    blkCnt = blockSize;
  
    while(blkCnt > 0u)
    {
      /* f0(n) = x(n) */
      fcurr = *pSrc++;
  
      /* Initialize coeff pointer */
      pk = (pCoeffs);
  
      /* Initialize state pointer */
      px = pState;
  
      /* read g0(n-1) from state buffer */
      gcurr = *px;
  
      /* for sample 1 processing */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext = (q31_t) (((q63_t) gcurr * (*pk)) >> 31) + fcurr;
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext = (q31_t) (((q63_t) fcurr * (*pk++)) >> 31) + gcurr;
      /* save g1(n) in state buffer */
      *px++ = fcurr;
  
      /* f1(n) is saved in fcurr1            
         for next stage processing */
      fcurr = fnext;
  
      stageCnt = (numStages - 1u);
  
      /* stage loop */
      while(stageCnt > 0u)
      {
        /* read g2(n) from state buffer */
        gcurr = *px;
  
        /* save g1(n) in state buffer */
        *px++ = gnext;
  
        /* Sample processing for K2, K3.... */
        /* f2(n) = f1(n) +  K2 * g1(n-1) */
        fnext = (q31_t) (((q63_t) gcurr * (*pk)) >> 31) + fcurr;
        /* g2(n) = f1(n) * K2  +  g1(n-1) */
        gnext = (q31_t) (((q63_t) fcurr * (*pk++)) >> 31) + gcurr;
  
        /* f1(n) is saved in fcurr1            
           for next stage processing */
        fcurr = fnext;
  
        stageCnt--;
  
      }
  
      /* y(n) = fN(n) */
      *pDst++ = fcurr;
  
      blkCnt--;
  
    }
  
  }
  
  #endif /*   #ifndef ARM_MATH_CM0_FAMILY */
  
  
  /**    
   * @} end of FIR_Lattice group    
   */
  