text: /* ----------------------------------------------------------------------    
  * Copyright (C) 2010-2013 ARM Limited. All rights reserved.    
  *    
  * $Date:        17. January 2013
  * $Revision: 	V1.4.1
  *    
  * Project: 	    CMSIS DSP Library    
  * Title:	    arm_fir_lattice_q15.c    
  *    
  * Description:	Q15 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 Q15 FIR lattice filter.    
   * @param[in]  *S        points to an instance of the Q15 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.    
   */
  
  void arm_fir_lattice_q15(
    const arm_fir_lattice_instance_q15 * S,
    q15_t * pSrc,
    q15_t * pDst,
    uint32_t blockSize)
  {
    q15_t *pState;                                 /* State pointer */
    q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
    q15_t *px;                                     /* temporary state pointer */
    q15_t *pk;                                     /* temporary coefficient pointer */
  
  
  #ifndef ARM_MATH_CM0_FAMILY
  
    /* Run the below code for Cortex-M4 and Cortex-M3 */
  
    q31_t fcurnt1, fnext1, gcurnt1 = 0, gnext1;    /* temporary variables for first sample in loop unrolling */
    q31_t fcurnt2, fnext2, gnext2;                 /* temporary variables for second sample in loop unrolling */
    q31_t fcurnt3, fnext3, gnext3;                 /* temporary variables for third sample in loop unrolling */
    q31_t fcurnt4, fnext4, gnext4;                 /* temporary variables for fourth sample in loop unrolling */
    uint32_t numStages = S->numStages;             /* Number of stages in the filter */
    uint32_t blkCnt, stageCnt;                     /* temporary variables for counts */
  
    pState = &S->pState[0];
  
    blkCnt = blockSize >> 2u;
  
    /* 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)
    {
  
      /* Read two samples from input buffer */
      /* f0(n) = x(n) */
      fcurnt1 = *pSrc++;
      fcurnt2 = *pSrc++;
  
      /* Initialize coeff pointer */
      pk = (pCoeffs);
  
      /* Initialize state pointer */
      px = pState;
  
      /* Read g0(n-1) from state */
      gcurnt1 = *px;
  
      /* Process first sample for first tap */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext1 = (q31_t) ((gcurnt1 * (*pk)) >> 15u) + fcurnt1;
      fnext1 = __SSAT(fnext1, 16);
  
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext1 = (q31_t) ((fcurnt1 * (*pk)) >> 15u) + gcurnt1;
      gnext1 = __SSAT(gnext1, 16);
  
      /* Process second sample for first tap */
      /* for sample 2 processing */
      fnext2 = (q31_t) ((fcurnt1 * (*pk)) >> 15u) + fcurnt2;
      fnext2 = __SSAT(fnext2, 16);
  
      gnext2 = (q31_t) ((fcurnt2 * (*pk)) >> 15u) + fcurnt1;
      gnext2 = __SSAT(gnext2, 16);
  
  
      /* Read next two samples from input buffer */
      /* f0(n+2) = x(n+2) */
      fcurnt3 = *pSrc++;
      fcurnt4 = *pSrc++;
  
      /* Copy only last input samples into the state buffer    
         which is used for next four samples processing */
      *px++ = (q15_t) fcurnt4;
  
      /* Process third sample for first tap */
      fnext3 = (q31_t) ((fcurnt2 * (*pk)) >> 15u) + fcurnt3;
      fnext3 = __SSAT(fnext3, 16);
      gnext3 = (q31_t) ((fcurnt3 * (*pk)) >> 15u) + fcurnt2;
      gnext3 = __SSAT(gnext3, 16);
  
      /* Process fourth sample for first tap */
      fnext4 = (q31_t) ((fcurnt3 * (*pk)) >> 15u) + fcurnt4;
      fnext4 = __SSAT(fnext4, 16);
      gnext4 = (q31_t) ((fcurnt4 * (*pk++)) >> 15u) + fcurnt3;
      gnext4 = __SSAT(gnext4, 16);
  
      /* Update of f values for next coefficient set processing */
      fcurnt1 = fnext1;
      fcurnt2 = fnext2;
      fcurnt3 = fnext3;
      fcurnt4 = fnext4;
  
  
      /* Loop unrolling.  Process 4 taps at a time . */
      stageCnt = (numStages - 1u) >> 2;
  
  
      /* Loop over the number of taps.  Unroll by a factor of 4.    
       ** Repeat until we've computed numStages-3 coefficients. */
  
      /* Process 2nd, 3rd, 4th and 5th taps ... here */
      while(stageCnt > 0u)
      {
        /* Read g1(n-1), g3(n-1) .... from state */
        gcurnt1 = *px;
  
        /* save g1(n) in state buffer */
        *px++ = (q15_t) gnext4;
  
        /* Process first sample for 2nd, 6th .. tap */
        /* Sample processing for K2, K6.... */
        /* f1(n) = f0(n) +  K1 * g0(n-1) */
        fnext1 = (q31_t) ((gcurnt1 * (*pk)) >> 15u) + fcurnt1;
        fnext1 = __SSAT(fnext1, 16);
  
  
        /* Process second sample for 2nd, 6th .. tap */
        /* for sample 2 processing */
        fnext2 = (q31_t) ((gnext1 * (*pk)) >> 15u) + fcurnt2;
        fnext2 = __SSAT(fnext2, 16);
        /* Process third sample for 2nd, 6th .. tap */
        fnext3 = (q31_t) ((gnext2 * (*pk)) >> 15u) + fcurnt3;
        fnext3 = __SSAT(fnext3, 16);
        /* Process fourth sample for 2nd, 6th .. tap */
        /* fnext4 = fcurnt4 + (*pk) * gnext3; */
        fnext4 = (q31_t) ((gnext3 * (*pk)) >> 15u) + fcurnt4;
        fnext4 = __SSAT(fnext4, 16);
  
        /* g1(n) = f0(n) * K1  +  g0(n-1) */
        /* Calculation of state values for next stage */
        gnext4 = (q31_t) ((fcurnt4 * (*pk)) >> 15u) + gnext3;
        gnext4 = __SSAT(gnext4, 16);
        gnext3 = (q31_t) ((fcurnt3 * (*pk)) >> 15u) + gnext2;
        gnext3 = __SSAT(gnext3, 16);
  
        gnext2 = (q31_t) ((fcurnt2 * (*pk)) >> 15u) + gnext1;
        gnext2 = __SSAT(gnext2, 16);
  
        gnext1 = (q31_t) ((fcurnt1 * (*pk++)) >> 15u) + gcurnt1;
        gnext1 = __SSAT(gnext1, 16);
  
  
        /* Read g2(n-1), g4(n-1) .... from state */
        gcurnt1 = *px;
  
        /* save g1(n) in state buffer */
        *px++ = (q15_t) gnext4;
  
        /* Sample processing for K3, K7.... */
        /* Process first sample for 3rd, 7th .. tap */
        /* f3(n) = f2(n) +  K3 * g2(n-1) */
        fcurnt1 = (q31_t) ((gcurnt1 * (*pk)) >> 15u) + fnext1;
        fcurnt1 = __SSAT(fcurnt1, 16);
  
        /* Process second sample for 3rd, 7th .. tap */
        fcurnt2 = (q31_t) ((gnext1 * (*pk)) >> 15u) + fnext2;
        fcurnt2 = __SSAT(fcurnt2, 16);
  
        /* Process third sample for 3rd, 7th .. tap */
        fcurnt3 = (q31_t) ((gnext2 * (*pk)) >> 15u) + fnext3;
        fcurnt3 = __SSAT(fcurnt3, 16);
  
        /* Process fourth sample for 3rd, 7th .. tap */
        fcurnt4 = (q31_t) ((gnext3 * (*pk)) >> 15u) + fnext4;
        fcurnt4 = __SSAT(fcurnt4, 16);
  
        /* Calculation of state values for next stage */
        /* g3(n) = f2(n) * K3  +  g2(n-1) */
        gnext4 = (q31_t) ((fnext4 * (*pk)) >> 15u) + gnext3;
        gnext4 = __SSAT(gnext4, 16);
  
        gnext3 = (q31_t) ((fnext3 * (*pk)) >> 15u) + gnext2;
        gnext3 = __SSAT(gnext3, 16);
  
        gnext2 = (q31_t) ((fnext2 * (*pk)) >> 15u) + gnext1;
        gnext2 = __SSAT(gnext2, 16);
  
        gnext1 = (q31_t) ((fnext1 * (*pk++)) >> 15u) + gcurnt1;
        gnext1 = __SSAT(gnext1, 16);
  
        /* Read g1(n-1), g3(n-1) .... from state */
        gcurnt1 = *px;
  
        /* save g1(n) in state buffer */
        *px++ = (q15_t) gnext4;
  
        /* Sample processing for K4, K8.... */
        /* Process first sample for 4th, 8th .. tap */
        /* f4(n) = f3(n) +  K4 * g3(n-1) */
        fnext1 = (q31_t) ((gcurnt1 * (*pk)) >> 15u) + fcurnt1;
        fnext1 = __SSAT(fnext1, 16);
  
        /* Process second sample for 4th, 8th .. tap */
        /* for sample 2 processing */
        fnext2 = (q31_t) ((gnext1 * (*pk)) >> 15u) + fcurnt2;
        fnext2 = __SSAT(fnext2, 16);
  
        /* Process third sample for 4th, 8th .. tap */
        fnext3 = (q31_t) ((gnext2 * (*pk)) >> 15u) + fcurnt3;
        fnext3 = __SSAT(fnext3, 16);
  
        /* Process fourth sample for 4th, 8th .. tap */
        fnext4 = (q31_t) ((gnext3 * (*pk)) >> 15u) + fcurnt4;
        fnext4 = __SSAT(fnext4, 16);
  
        /* g4(n) = f3(n) * K4  +  g3(n-1) */
        /* Calculation of state values for next stage */
        gnext4 = (q31_t) ((fcurnt4 * (*pk)) >> 15u) + gnext3;
        gnext4 = __SSAT(gnext4, 16);
  
        gnext3 = (q31_t) ((fcurnt3 * (*pk)) >> 15u) + gnext2;
        gnext3 = __SSAT(gnext3, 16);
  
        gnext2 = (q31_t) ((fcurnt2 * (*pk)) >> 15u) + gnext1;
        gnext2 = __SSAT(gnext2, 16);
        gnext1 = (q31_t) ((fcurnt1 * (*pk++)) >> 15u) + gcurnt1;
        gnext1 = __SSAT(gnext1, 16);
  
  
        /* Read g2(n-1), g4(n-1) .... from state */
        gcurnt1 = *px;
  
        /* save g4(n) in state buffer */
        *px++ = (q15_t) gnext4;
  
        /* Sample processing for K5, K9.... */
        /* Process first sample for 5th, 9th .. tap */
        /* f5(n) = f4(n) +  K5 * g4(n-1) */
        fcurnt1 = (q31_t) ((gcurnt1 * (*pk)) >> 15u) + fnext1;
        fcurnt1 = __SSAT(fcurnt1, 16);
  
        /* Process second sample for 5th, 9th .. tap */
        fcurnt2 = (q31_t) ((gnext1 * (*pk)) >> 15u) + fnext2;
        fcurnt2 = __SSAT(fcurnt2, 16);
  
        /* Process third sample for 5th, 9th .. tap */
        fcurnt3 = (q31_t) ((gnext2 * (*pk)) >> 15u) + fnext3;
        fcurnt3 = __SSAT(fcurnt3, 16);
  
        /* Process fourth sample for 5th, 9th .. tap */
        fcurnt4 = (q31_t) ((gnext3 * (*pk)) >> 15u) + fnext4;
        fcurnt4 = __SSAT(fcurnt4, 16);
  
        /* Calculation of state values for next stage */
        /* g5(n) = f4(n) * K5  +  g4(n-1) */
        gnext4 = (q31_t) ((fnext4 * (*pk)) >> 15u) + gnext3;
        gnext4 = __SSAT(gnext4, 16);
        gnext3 = (q31_t) ((fnext3 * (*pk)) >> 15u) + gnext2;
        gnext3 = __SSAT(gnext3, 16);
        gnext2 = (q31_t) ((fnext2 * (*pk)) >> 15u) + gnext1;
        gnext2 = __SSAT(gnext2, 16);
        gnext1 = (q31_t) ((fnext1 * (*pk++)) >> 15u) + gcurnt1;
        gnext1 = __SSAT(gnext1, 16);
  
        stageCnt--;
      }
  
      /* If the (filter length -1) is not a multiple of 4, compute the remaining filter taps */
      stageCnt = (numStages - 1u) % 0x4u;
  
      while(stageCnt > 0u)
      {
        gcurnt1 = *px;
  
        /* save g value in state buffer */
        *px++ = (q15_t) gnext4;
  
        /* Process four samples for last three taps here */
        fnext1 = (q31_t) ((gcurnt1 * (*pk)) >> 15u) + fcurnt1;
        fnext1 = __SSAT(fnext1, 16);
        fnext2 = (q31_t) ((gnext1 * (*pk)) >> 15u) + fcurnt2;
        fnext2 = __SSAT(fnext2, 16);
  
        fnext3 = (q31_t) ((gnext2 * (*pk)) >> 15u) + fcurnt3;
        fnext3 = __SSAT(fnext3, 16);
  
        fnext4 = (q31_t) ((gnext3 * (*pk)) >> 15u) + fcurnt4;
        fnext4 = __SSAT(fnext4, 16);
  
        /* g1(n) = f0(n) * K1  +  g0(n-1) */
        gnext4 = (q31_t) ((fcurnt4 * (*pk)) >> 15u) + gnext3;
        gnext4 = __SSAT(gnext4, 16);
        gnext3 = (q31_t) ((fcurnt3 * (*pk)) >> 15u) + gnext2;
        gnext3 = __SSAT(gnext3, 16);
        gnext2 = (q31_t) ((fcurnt2 * (*pk)) >> 15u) + gnext1;
        gnext2 = __SSAT(gnext2, 16);
        gnext1 = (q31_t) ((fcurnt1 * (*pk++)) >> 15u) + gcurnt1;
        gnext1 = __SSAT(gnext1, 16);
  
        /* Update of f values for next coefficient set processing */
        fcurnt1 = fnext1;
        fcurnt2 = fnext2;
        fcurnt3 = fnext3;
        fcurnt4 = fnext4;
  
        stageCnt--;
  
      }
  
      /* The results in the 4 accumulators, store in the destination buffer. */
      /* y(n) = fN(n) */
  
  #ifndef  ARM_MATH_BIG_ENDIAN
  
      *__SIMD32(pDst)++ = __PKHBT(fcurnt1, fcurnt2, 16);
      *__SIMD32(pDst)++ = __PKHBT(fcurnt3, fcurnt4, 16);
  
  #else
  
      *__SIMD32(pDst)++ = __PKHBT(fcurnt2, fcurnt1, 16);
      *__SIMD32(pDst)++ = __PKHBT(fcurnt4, fcurnt3, 16);
  
  #endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */
  
      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)
    {
      /* f0(n) = x(n) */
      fcurnt1 = *pSrc++;
  
      /* Initialize coeff pointer */
      pk = (pCoeffs);
  
      /* Initialize state pointer */
      px = pState;
  
      /* read g2(n) from state buffer */
      gcurnt1 = *px;
  
      /* for sample 1 processing */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext1 = (((q31_t) gcurnt1 * (*pk)) >> 15u) + fcurnt1;
      fnext1 = __SSAT(fnext1, 16);
  
  
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext1 = (((q31_t) fcurnt1 * (*pk++)) >> 15u) + gcurnt1;
      gnext1 = __SSAT(gnext1, 16);
  
      /* save g1(n) in state buffer */
      *px++ = (q15_t) fcurnt1;
  
      /* f1(n) is saved in fcurnt1    
         for next stage processing */
      fcurnt1 = fnext1;
  
      stageCnt = (numStages - 1u);
  
      /* stage loop */
      while(stageCnt > 0u)
      {
        /* read g2(n) from state buffer */
        gcurnt1 = *px;
  
        /* save g1(n) in state buffer */
        *px++ = (q15_t) gnext1;
  
        /* Sample processing for K2, K3.... */
        /* f2(n) = f1(n) +  K2 * g1(n-1) */
        fnext1 = (((q31_t) gcurnt1 * (*pk)) >> 15u) + fcurnt1;
        fnext1 = __SSAT(fnext1, 16);
  
        /* g2(n) = f1(n) * K2  +  g1(n-1) */
        gnext1 = (((q31_t) fcurnt1 * (*pk++)) >> 15u) + gcurnt1;
        gnext1 = __SSAT(gnext1, 16);
  
  
        /* f1(n) is saved in fcurnt1    
           for next stage processing */
        fcurnt1 = fnext1;
  
        stageCnt--;
  
      }
  
      /* y(n) = fN(n) */
      *pDst++ = __SSAT(fcurnt1, 16);
  
  
      blkCnt--;
  
    }
  
  #else
  
    /* Run the below code for Cortex-M0 */
  
    q31_t fcurnt, fnext, gcurnt, 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) */
      fcurnt = *pSrc++;
  
      /* Initialize coeff pointer */
      pk = (pCoeffs);
  
      /* Initialize state pointer */
      px = pState;
  
      /* read g0(n-1) from state buffer */
      gcurnt = *px;
  
      /* for sample 1 processing */
      /* f1(n) = f0(n) +  K1 * g0(n-1) */
      fnext = ((gcurnt * (*pk)) >> 15u) + fcurnt;
      fnext = __SSAT(fnext, 16);
  
  
      /* g1(n) = f0(n) * K1  +  g0(n-1) */
      gnext = ((fcurnt * (*pk++)) >> 15u) + gcurnt;
      gnext = __SSAT(gnext, 16);
  
      /* save f0(n) in state buffer */
      *px++ = (q15_t) fcurnt;
  
      /* f1(n) is saved in fcurnt            
         for next stage processing */
      fcurnt = fnext;
  
      stageCnt = (numStages - 1u);
  
      /* stage loop */
      while(stageCnt > 0u)
      {
        /* read g1(n-1) from state buffer */
        gcurnt = *px;
  
        /* save g0(n-1) in state buffer */
        *px++ = (q15_t) gnext;
  
        /* Sample processing for K2, K3.... */
        /* f2(n) = f1(n) +  K2 * g1(n-1) */
        fnext = ((gcurnt * (*pk)) >> 15u) + fcurnt;
        fnext = __SSAT(fnext, 16);
  
        /* g2(n) = f1(n) * K2  +  g1(n-1) */
        gnext = ((fcurnt * (*pk++)) >> 15u) + gcurnt;
        gnext = __SSAT(gnext, 16);
  
  
        /* f1(n) is saved in fcurnt            
           for next stage processing */
        fcurnt = fnext;
  
        stageCnt--;
  
      }
  
      /* y(n) = fN(n) */
      *pDst++ = __SSAT(fcurnt, 16);
  
  
      blkCnt--;
  
    }
  
  #endif /*   #ifndef ARM_MATH_CM0_FAMILY */
  
  }
  
  /**    
   * @} end of FIR_Lattice group    
   */
  