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_correlate_fast_q15.c
  *
  * Description:	Fast Q15 Correlation.
  *
  * Target Processor: Cortex-M4/Cortex-M3
  *
  * 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 Corr
   * @{
   */
  
  /**
   * @brief Correlation of Q15 sequences (fast version) for Cortex-M3 and Cortex-M4.
   * @param[in] *pSrcA points to the first input sequence.
   * @param[in] srcALen length of the first input sequence.
   * @param[in] *pSrcB points to the second input sequence.
   * @param[in] srcBLen length of the second input sequence.
   * @param[out] *pDst points to the location where the output result is written.  Length 2 * max(srcALen, srcBLen) - 1.
   * @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.
   * There is no saturation on intermediate additions.
   * Thus, if the accumulator overflows it wraps around and distorts the result.
   * The input signals should be scaled down to avoid intermediate overflows.
   * Scale down one of the inputs by 1/min(srcALen, srcBLen) to avoid overflow since a
   * maximum of min(srcALen, srcBLen) number of additions is carried internally.
   * The 2.30 accumulator is right shifted by 15 bits and then saturated to 1.15 format to yield the final result.
   *
   * \par
   * See <code>arm_correlate_q15()</code> for a slower implementation of this function which uses a 64-bit accumulator to avoid wrap around distortion.
   */
  
  void arm_correlate_fast_q15(
    q15_t * pSrcA,
    uint32_t srcALen,
    q15_t * pSrcB,
    uint32_t srcBLen,
    q15_t * pDst)
  {
  #ifndef UNALIGNED_SUPPORT_DISABLE
  
    q15_t *pIn1;                                   /* inputA pointer               */
    q15_t *pIn2;                                   /* inputB pointer               */
    q15_t *pOut = pDst;                            /* output pointer               */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulators                  */
    q15_t *px;                                     /* Intermediate inputA pointer  */
    q15_t *py;                                     /* Intermediate inputB pointer  */
    q15_t *pSrc1;                                  /* Intermediate pointers        */
    q31_t x0, x1, x2, x3, c0;                      /* temporary variables for holding input and coefficient values */
    uint32_t j, k = 0u, count, blkCnt, outBlockSize, blockSize1, blockSize2, blockSize3;  /* loop counter                 */
    int32_t inc = 1;                               /* Destination address modifier */
  
  
    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    /* But CORR(x, y) is reverse of CORR(y, x) */
    /* So, when srcBLen > srcALen, output pointer is made to point to the end of the output buffer */
    /* and the destination pointer modifier, inc is set to -1 */
    /* If srcALen > srcBLen, zero pad has to be done to srcB to make the two inputs of same length */
    /* But to improve the performance,
     * we include zeroes in the output instead of zero padding either of the the inputs*/
    /* If srcALen > srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the starting of the output buffer */
    /* If srcALen < srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the ending of the output buffer */
    if(srcALen >= srcBLen)
    {
      /* Initialization of inputA pointer */
      pIn1 = (pSrcA);
  
      /* Initialization of inputB pointer */
      pIn2 = (pSrcB);
  
      /* Number of output samples is calculated */
      outBlockSize = (2u * srcALen) - 1u;
  
      /* When srcALen > srcBLen, zero padding is done to srcB
       * to make their lengths equal.
       * Instead, (outBlockSize - (srcALen + srcBLen - 1))
       * number of output samples are made zero */
      j = outBlockSize - (srcALen + (srcBLen - 1u));
  
      /* Updating the pointer position to non zero value */
      pOut += j;
  
    }
    else
    {
      /* Initialization of inputA pointer */
      pIn1 = (pSrcB);
  
      /* Initialization of inputB pointer */
      pIn2 = (pSrcA);
  
      /* srcBLen is always considered as shorter or equal to srcALen */
      j = srcBLen;
      srcBLen = srcALen;
      srcALen = j;
  
      /* CORR(x, y) = Reverse order(CORR(y, x)) */
      /* Hence set the destination pointer to point to the last output sample */
      pOut = pDst + ((srcALen + srcBLen) - 2u);
  
      /* Destination address modifier is set to -1 */
      inc = -1;
  
    }
  
    /* The function is internally
     * divided into three parts according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first part of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second part of the algorithm, srcBLen number of multiplications are done.
     * In the third part of the algorithm, the multiplications decrease by one
     * for every iteration.*/
    /* The algorithm is implemented in three stages.
     * The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;
  
    /* --------------------------
     * Initializations of stage1
     * -------------------------*/
  
    /* sum = x[0] * y[srcBlen - 1]
     * sum = x[0] * y[srcBlen - 2] + x[1] * y[srcBlen - 1]
     * ....
     * sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen - 1] * y[srcBLen - 1]
     */
  
    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;
  
    /* Working pointer of inputA */
    px = pIn1;
  
    /* Working pointer of inputB */
    pSrc1 = pIn2 + (srcBLen - 1u);
    py = pSrc1;
  
    /* ------------------------
     * Stage1 process
     * ----------------------*/
  
    /* The first loop starts here */
    while(blockSize1 > 0u)
    {
      /* Accumulator is made zero for every iteration */
      sum = 0;
  
      /* Apply loop unrolling and compute 4 MACs simultaneously. */
      k = count >> 2;
  
      /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
       ** a second loop below computes MACs for the remaining 1 to 3 samples. */
      while(k > 0u)
      {
        /* x[0] * y[srcBLen - 4] , x[1] * y[srcBLen - 3] */
        sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
        /* x[3] * y[srcBLen - 1] , x[2] * y[srcBLen - 2] */
        sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* If the count is not a multiple of 4, compute any remaining MACs here.
       ** No loop unrolling is used. */
      k = count % 0x4u;
  
      while(k > 0u)
      {
        /* Perform the multiply-accumulates */
        /* x[0] * y[srcBLen - 1] */
        sum = __SMLAD(*px++, *py++, sum);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* Store the result in the accumulator in the destination buffer. */
      *pOut = (q15_t) (sum >> 15);
      /* Destination pointer is updated according to the address modifier, inc */
      pOut += inc;
  
      /* Update the inputA and inputB pointers for next MAC calculation */
      py = pSrc1 - count;
      px = pIn1;
  
      /* Increment the MAC count */
      count++;
  
      /* Decrement the loop counter */
      blockSize1--;
    }
  
    /* --------------------------
     * Initializations of stage2
     * ------------------------*/
  
    /* sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen-1] * y[srcBLen-1]
     * sum = x[1] * y[0] + x[2] * y[1] +...+ x[srcBLen] * y[srcBLen-1]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[0] + x[srcALen-srcBLen-1] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     */
  
    /* Working pointer of inputA */
    px = pIn1;
  
    /* Working pointer of inputB */
    py = pIn2;
  
    /* count is index by which the pointer pIn1 to be incremented */
    count = 0u;
  
    /* -------------------
     * Stage2 process
     * ------------------*/
  
    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4, to loop unroll the srcBLen loop */
    if(srcBLen >= 4u)
    {
      /* Loop unroll over blockSize2, by 4 */
      blkCnt = blockSize2 >> 2u;
  
      while(blkCnt > 0u)
      {
        /* Set all accumulators to zero */
        acc0 = 0;
        acc1 = 0;
        acc2 = 0;
        acc3 = 0;
  
        /* read x[0], x[1] samples */
        x0 = *__SIMD32(px);
        /* read x[1], x[2] samples */
        x1 = _SIMD32_OFFSET(px + 1);
  	  px += 2u;
  
        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = srcBLen >> 2u;
  
        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        do
        {
          /* Read the first two inputB samples using SIMD:
           * y[0] and y[1] */
          c0 = *__SIMD32(py)++;
  
          /* acc0 +=  x[0] * y[0] + x[1] * y[1] */
          acc0 = __SMLAD(x0, c0, acc0);
  
          /* acc1 +=  x[1] * y[0] + x[2] * y[1] */
          acc1 = __SMLAD(x1, c0, acc1);
  
          /* Read x[2], x[3] */
          x2 = *__SIMD32(px);
  
          /* Read x[3], x[4] */
          x3 = _SIMD32_OFFSET(px + 1);
  
          /* acc2 +=  x[2] * y[0] + x[3] * y[1] */
          acc2 = __SMLAD(x2, c0, acc2);
  
          /* acc3 +=  x[3] * y[0] + x[4] * y[1] */
          acc3 = __SMLAD(x3, c0, acc3);
  
          /* Read y[2] and y[3] */
          c0 = *__SIMD32(py)++;
  
          /* acc0 +=  x[2] * y[2] + x[3] * y[3] */
          acc0 = __SMLAD(x2, c0, acc0);
  
          /* acc1 +=  x[3] * y[2] + x[4] * y[3] */
          acc1 = __SMLAD(x3, c0, acc1);
  
          /* Read x[4], x[5] */
          x0 = _SIMD32_OFFSET(px + 2);
  
          /* Read x[5], x[6] */
          x1 = _SIMD32_OFFSET(px + 3);
  		px += 4u;
  
          /* acc2 +=  x[4] * y[2] + x[5] * y[3] */
          acc2 = __SMLAD(x0, c0, acc2);
  
          /* acc3 +=  x[5] * y[2] + x[6] * y[3] */
          acc3 = __SMLAD(x1, c0, acc3);
  
        } while(--k);
  
        /* For the next MAC operations, SIMD is not used
         * So, the 16 bit pointer if inputB, py is updated */
  
        /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = srcBLen % 0x4u;
  
        if(k == 1u)
        {
          /* Read y[4] */
          c0 = *py;
  #ifdef  ARM_MATH_BIG_ENDIAN
  
          c0 = c0 << 16u;
  
  #else
  
          c0 = c0 & 0x0000FFFF;
  
  #endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */
  
          /* Read x[7] */
          x3 = *__SIMD32(px);
  		px++;
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLAD(x0, c0, acc0);
          acc1 = __SMLAD(x1, c0, acc1);
          acc2 = __SMLADX(x1, c0, acc2);
          acc3 = __SMLADX(x3, c0, acc3);
        }
  
        if(k == 2u)
        {
          /* Read y[4], y[5] */
          c0 = *__SIMD32(py);
  
          /* Read x[7], x[8] */
          x3 = *__SIMD32(px);
  
          /* Read x[9] */
          x2 = _SIMD32_OFFSET(px + 1);
  		px += 2u;
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLAD(x0, c0, acc0);
          acc1 = __SMLAD(x1, c0, acc1);
          acc2 = __SMLAD(x3, c0, acc2);
          acc3 = __SMLAD(x2, c0, acc3);
        }
  
        if(k == 3u)
        {
          /* Read y[4], y[5] */
          c0 = *__SIMD32(py)++;
  
          /* Read x[7], x[8] */
          x3 = *__SIMD32(px);
  
          /* Read x[9] */
          x2 = _SIMD32_OFFSET(px + 1);
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLAD(x0, c0, acc0);
          acc1 = __SMLAD(x1, c0, acc1);
          acc2 = __SMLAD(x3, c0, acc2);
          acc3 = __SMLAD(x2, c0, acc3);
  
          c0 = (*py);
          /* Read y[6] */
  #ifdef  ARM_MATH_BIG_ENDIAN
  
          c0 = c0 << 16u;
  #else
  
          c0 = c0 & 0x0000FFFF;
  #endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */
  
          /* Read x[10] */
          x3 = _SIMD32_OFFSET(px + 2);
  		px += 3u;
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLADX(x1, c0, acc0);
          acc1 = __SMLAD(x2, c0, acc1);
          acc2 = __SMLADX(x2, c0, acc2);
          acc3 = __SMLADX(x3, c0, acc3);
        }
  
        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (acc0 >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;
  
        *pOut = (q15_t) (acc1 >> 15);
        pOut += inc;
  
        *pOut = (q15_t) (acc2 >> 15);
        pOut += inc;
  
        *pOut = (q15_t) (acc3 >> 15);
        pOut += inc;
  
        /* Increment the pointer pIn1 index, count by 1 */
        count += 4u;
  
        /* Update the inputA and inputB pointers for next MAC calculation */
        px = pIn1 + count;
        py = pIn2;
  
  
        /* Decrement the loop counter */
        blkCnt--;
      }
  
      /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
       ** No loop unrolling is used. */
      blkCnt = blockSize2 % 0x4u;
  
      while(blkCnt > 0u)
      {
        /* Accumulator is made zero for every iteration */
        sum = 0;
  
        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = srcBLen >> 2u;
  
        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
          /* Perform the multiply-accumulates */
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
  
          /* Decrement the loop counter */
          k--;
        }
  
        /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = srcBLen % 0x4u;
  
        while(k > 0u)
        {
          /* Perform the multiply-accumulates */
          sum += ((q31_t) * px++ * *py++);
  
          /* Decrement the loop counter */
          k--;
        }
  
        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;
  
        /* Increment the pointer pIn1 index, count by 1 */
        count++;
  
        /* Update the inputA and inputB pointers for next MAC calculation */
        px = pIn1 + count;
        py = pIn2;
  
        /* Decrement the loop counter */
        blkCnt--;
      }
    }
    else
    {
      /* If the srcBLen is not a multiple of 4,
       * the blockSize2 loop cannot be unrolled by 4 */
      blkCnt = blockSize2;
  
      while(blkCnt > 0u)
      {
        /* Accumulator is made zero for every iteration */
        sum = 0;
  
        /* Loop over srcBLen */
        k = srcBLen;
  
        while(k > 0u)
        {
          /* Perform the multiply-accumulate */
          sum += ((q31_t) * px++ * *py++);
  
          /* Decrement the loop counter */
          k--;
        }
  
        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;
  
        /* Increment the MAC count */
        count++;
  
        /* Update the inputA and inputB pointers for next MAC calculation */
        px = pIn1 + count;
        py = pIn2;
  
        /* Decrement the loop counter */
        blkCnt--;
      }
    }
  
    /* --------------------------
     * Initializations of stage3
     * -------------------------*/
  
    /* sum += x[srcALen-srcBLen+1] * y[0] + x[srcALen-srcBLen+2] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * sum += x[srcALen-srcBLen+2] * y[0] + x[srcALen-srcBLen+3] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * ....
     * sum +=  x[srcALen-2] * y[0] + x[srcALen-1] * y[1]
     * sum +=  x[srcALen-1] * y[0]
     */
  
    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = srcBLen - 1u;
  
    /* Working pointer of inputA */
    pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
    px = pSrc1;
  
    /* Working pointer of inputB */
    py = pIn2;
  
    /* -------------------
     * Stage3 process
     * ------------------*/
  
    while(blockSize3 > 0u)
    {
      /* Accumulator is made zero for every iteration */
      sum = 0;
  
      /* Apply loop unrolling and compute 4 MACs simultaneously. */
      k = count >> 2u;
  
      /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
       ** a second loop below computes MACs for the remaining 1 to 3 samples. */
      while(k > 0u)
      {
        /* Perform the multiply-accumulates */
        /* sum += x[srcALen - srcBLen + 4] * y[3] , sum += x[srcALen - srcBLen + 3] * y[2] */
        sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
        /* sum += x[srcALen - srcBLen + 2] * y[1] , sum += x[srcALen - srcBLen + 1] * y[0] */
        sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* If the count is not a multiple of 4, compute any remaining MACs here.
       ** No loop unrolling is used. */
      k = count % 0x4u;
  
      while(k > 0u)
      {
        /* Perform the multiply-accumulates */
        sum = __SMLAD(*px++, *py++, sum);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* Store the result in the accumulator in the destination buffer. */
      *pOut = (q15_t) (sum >> 15);
      /* Destination pointer is updated according to the address modifier, inc */
      pOut += inc;
  
      /* Update the inputA and inputB pointers for next MAC calculation */
      px = ++pSrc1;
      py = pIn2;
  
      /* Decrement the MAC count */
      count--;
  
      /* Decrement the loop counter */
      blockSize3--;
    }
  
  #else
  
    q15_t *pIn1;                                   /* inputA pointer               */
    q15_t *pIn2;                                   /* inputB pointer               */
    q15_t *pOut = pDst;                            /* output pointer               */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulators                  */
    q15_t *px;                                     /* Intermediate inputA pointer  */
    q15_t *py;                                     /* Intermediate inputB pointer  */
    q15_t *pSrc1;                                  /* Intermediate pointers        */
    q31_t x0, x1, x2, x3, c0;                      /* temporary variables for holding input and coefficient values */
    uint32_t j, k = 0u, count, blkCnt, outBlockSize, blockSize1, blockSize2, blockSize3;  /* loop counter                 */
    int32_t inc = 1;                               /* Destination address modifier */
    q15_t a, b;
  
  
    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    /* But CORR(x, y) is reverse of CORR(y, x) */
    /* So, when srcBLen > srcALen, output pointer is made to point to the end of the output buffer */
    /* and the destination pointer modifier, inc is set to -1 */
    /* If srcALen > srcBLen, zero pad has to be done to srcB to make the two inputs of same length */
    /* But to improve the performance,
     * we include zeroes in the output instead of zero padding either of the the inputs*/
    /* If srcALen > srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the starting of the output buffer */
    /* If srcALen < srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the ending of the output buffer */
    if(srcALen >= srcBLen)
    {
      /* Initialization of inputA pointer */
      pIn1 = (pSrcA);
  
      /* Initialization of inputB pointer */
      pIn2 = (pSrcB);
  
      /* Number of output samples is calculated */
      outBlockSize = (2u * srcALen) - 1u;
  
      /* When srcALen > srcBLen, zero padding is done to srcB
       * to make their lengths equal.
       * Instead, (outBlockSize - (srcALen + srcBLen - 1))
       * number of output samples are made zero */
      j = outBlockSize - (srcALen + (srcBLen - 1u));
  
      /* Updating the pointer position to non zero value */
      pOut += j;
  
    }
    else
    {
      /* Initialization of inputA pointer */
      pIn1 = (pSrcB);
  
      /* Initialization of inputB pointer */
      pIn2 = (pSrcA);
  
      /* srcBLen is always considered as shorter or equal to srcALen */
      j = srcBLen;
      srcBLen = srcALen;
      srcALen = j;
  
      /* CORR(x, y) = Reverse order(CORR(y, x)) */
      /* Hence set the destination pointer to point to the last output sample */
      pOut = pDst + ((srcALen + srcBLen) - 2u);
  
      /* Destination address modifier is set to -1 */
      inc = -1;
  
    }
  
    /* The function is internally
     * divided into three parts according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first part of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second part of the algorithm, srcBLen number of multiplications are done.
     * In the third part of the algorithm, the multiplications decrease by one
     * for every iteration.*/
    /* The algorithm is implemented in three stages.
     * The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;
  
    /* --------------------------
     * Initializations of stage1
     * -------------------------*/
  
    /* sum = x[0] * y[srcBlen - 1]
     * sum = x[0] * y[srcBlen - 2] + x[1] * y[srcBlen - 1]
     * ....
     * sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen - 1] * y[srcBLen - 1]
     */
  
    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;
  
    /* Working pointer of inputA */
    px = pIn1;
  
    /* Working pointer of inputB */
    pSrc1 = pIn2 + (srcBLen - 1u);
    py = pSrc1;
  
    /* ------------------------
     * Stage1 process
     * ----------------------*/
  
    /* The first loop starts here */
    while(blockSize1 > 0u)
    {
      /* Accumulator is made zero for every iteration */
      sum = 0;
  
      /* Apply loop unrolling and compute 4 MACs simultaneously. */
      k = count >> 2;
  
      /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
       ** a second loop below computes MACs for the remaining 1 to 3 samples. */
      while(k > 0u)
      {
        /* x[0] * y[srcBLen - 4] , x[1] * y[srcBLen - 3] */
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* If the count is not a multiple of 4, compute any remaining MACs here.
       ** No loop unrolling is used. */
      k = count % 0x4u;
  
      while(k > 0u)
      {
        /* Perform the multiply-accumulates */
        /* x[0] * y[srcBLen - 1] */
          sum += ((q31_t) * px++ * *py++);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* Store the result in the accumulator in the destination buffer. */
      *pOut = (q15_t) (sum >> 15);
      /* Destination pointer is updated according to the address modifier, inc */
      pOut += inc;
  
      /* Update the inputA and inputB pointers for next MAC calculation */
      py = pSrc1 - count;
      px = pIn1;
  
      /* Increment the MAC count */
      count++;
  
      /* Decrement the loop counter */
      blockSize1--;
    }
  
    /* --------------------------
     * Initializations of stage2
     * ------------------------*/
  
    /* sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen-1] * y[srcBLen-1]
     * sum = x[1] * y[0] + x[2] * y[1] +...+ x[srcBLen] * y[srcBLen-1]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[0] + x[srcALen-srcBLen-1] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     */
  
    /* Working pointer of inputA */
    px = pIn1;
  
    /* Working pointer of inputB */
    py = pIn2;
  
    /* count is index by which the pointer pIn1 to be incremented */
    count = 0u;
  
    /* -------------------
     * Stage2 process
     * ------------------*/
  
    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4, to loop unroll the srcBLen loop */
    if(srcBLen >= 4u)
    {
      /* Loop unroll over blockSize2, by 4 */
      blkCnt = blockSize2 >> 2u;
  
      while(blkCnt > 0u)
      {
        /* Set all accumulators to zero */
        acc0 = 0;
        acc1 = 0;
        acc2 = 0;
        acc3 = 0;
  
        /* read x[0], x[1], x[2] samples */
  	  a = *px;
  	  b = *(px + 1);
  
  #ifndef ARM_MATH_BIG_ENDIAN
  
  	  x0 = __PKHBT(a, b, 16);
  	  a = *(px + 2);
  	  x1 = __PKHBT(b, a, 16);
  
  #else
  
  	  x0 = __PKHBT(b, a, 16);
  	  a = *(px + 2);
  	  x1 = __PKHBT(a, b, 16);
  
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
  	  px += 2u;
  
        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = srcBLen >> 2u;
  
        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        do
        {
          /* Read the first two inputB samples using SIMD:
           * y[0] and y[1] */
  		  a = *py;
  		  b = *(py + 1);
  	
  #ifndef ARM_MATH_BIG_ENDIAN
  	
  		  c0 = __PKHBT(a, b, 16);
  	
  #else
  	
  		  c0 = __PKHBT(b, a, 16);
  	
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
          /* acc0 +=  x[0] * y[0] + x[1] * y[1] */
          acc0 = __SMLAD(x0, c0, acc0);
  
          /* acc1 +=  x[1] * y[0] + x[2] * y[1] */
          acc1 = __SMLAD(x1, c0, acc1);
  
          /* Read x[2], x[3], x[4] */
  	  	a = *px;
  	  	b = *(px + 1);
  
  #ifndef ARM_MATH_BIG_ENDIAN
  
  	  	x2 = __PKHBT(a, b, 16);
  	  	a = *(px + 2);
  	  	x3 = __PKHBT(b, a, 16);
  
  #else
  
  	  	x2 = __PKHBT(b, a, 16);
  	  	a = *(px + 2);
  	  	x3 = __PKHBT(a, b, 16);
  
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
          /* acc2 +=  x[2] * y[0] + x[3] * y[1] */
          acc2 = __SMLAD(x2, c0, acc2);
  
          /* acc3 +=  x[3] * y[0] + x[4] * y[1] */
          acc3 = __SMLAD(x3, c0, acc3);
  
          /* Read y[2] and y[3] */
  		  a = *(py + 2);
  		  b = *(py + 3);
  
  		  py += 4u;
  	
  #ifndef ARM_MATH_BIG_ENDIAN
  	
  		  c0 = __PKHBT(a, b, 16);
  	
  #else
  	
  		  c0 = __PKHBT(b, a, 16);
  	
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
          /* acc0 +=  x[2] * y[2] + x[3] * y[3] */
          acc0 = __SMLAD(x2, c0, acc0);
  
          /* acc1 +=  x[3] * y[2] + x[4] * y[3] */
          acc1 = __SMLAD(x3, c0, acc1);
  
          /* Read x[4], x[5], x[6] */
  	  	a = *(px + 2);
  	  	b = *(px + 3);
  
  #ifndef ARM_MATH_BIG_ENDIAN
  
  	  	x0 = __PKHBT(a, b, 16);
  	  	a = *(px + 4);
  	  	x1 = __PKHBT(b, a, 16);
  
  #else
  
  	  	x0 = __PKHBT(b, a, 16);
  	  	a = *(px + 4);
  	  	x1 = __PKHBT(a, b, 16);
  
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
  		px += 4u;
  
          /* acc2 +=  x[4] * y[2] + x[5] * y[3] */
          acc2 = __SMLAD(x0, c0, acc2);
  
          /* acc3 +=  x[5] * y[2] + x[6] * y[3] */
          acc3 = __SMLAD(x1, c0, acc3);
  
        } while(--k);
  
        /* For the next MAC operations, SIMD is not used
         * So, the 16 bit pointer if inputB, py is updated */
  
        /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = srcBLen % 0x4u;
  
        if(k == 1u)
        {
          /* Read y[4] */
          c0 = *py;
  #ifdef  ARM_MATH_BIG_ENDIAN
  
          c0 = c0 << 16u;
  
  #else
  
          c0 = c0 & 0x0000FFFF;
  
  #endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */
  
          /* Read x[7] */
  		a = *px;
  		b = *(px + 1);
  
  		px++;;
  	
  #ifndef ARM_MATH_BIG_ENDIAN
  	
  		x3 = __PKHBT(a, b, 16);
  	
  #else
  	
  		x3 = __PKHBT(b, a, 16);
  	
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
  		px++;
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLAD(x0, c0, acc0);
          acc1 = __SMLAD(x1, c0, acc1);
          acc2 = __SMLADX(x1, c0, acc2);
          acc3 = __SMLADX(x3, c0, acc3);
        }
  
        if(k == 2u)
        {
          /* Read y[4], y[5] */
  		  a = *py;
  		  b = *(py + 1);
  	
  #ifndef ARM_MATH_BIG_ENDIAN
  	
  		  c0 = __PKHBT(a, b, 16);
  	
  #else
  	
  		  c0 = __PKHBT(b, a, 16);
  	
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
          /* Read x[7], x[8], x[9] */
  	  	a = *px;
  	  	b = *(px + 1);
  
  #ifndef ARM_MATH_BIG_ENDIAN
  
  	  	x3 = __PKHBT(a, b, 16);
  	  	a = *(px + 2);
  	  	x2 = __PKHBT(b, a, 16);
  
  #else
  
  	  	x3 = __PKHBT(b, a, 16);
  	  	a = *(px + 2);
  	  	x2 = __PKHBT(a, b, 16);
  
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
  		px += 2u;
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLAD(x0, c0, acc0);
          acc1 = __SMLAD(x1, c0, acc1);
          acc2 = __SMLAD(x3, c0, acc2);
          acc3 = __SMLAD(x2, c0, acc3);
        }
  
        if(k == 3u)
        {
          /* Read y[4], y[5] */
  		  a = *py;
  		  b = *(py + 1);
  	
  #ifndef ARM_MATH_BIG_ENDIAN
  	
  		  c0 = __PKHBT(a, b, 16);
  	
  #else
  	
  		  c0 = __PKHBT(b, a, 16);
  	
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
  		py += 2u;
  
          /* Read x[7], x[8], x[9] */
  	  	a = *px;
  	  	b = *(px + 1);
  
  #ifndef ARM_MATH_BIG_ENDIAN
  
  	  	x3 = __PKHBT(a, b, 16);
  	  	a = *(px + 2);
  	  	x2 = __PKHBT(b, a, 16);
  
  #else
  
  	  	x3 = __PKHBT(b, a, 16);
  	  	a = *(px + 2);
  	  	x2 = __PKHBT(a, b, 16);
  
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLAD(x0, c0, acc0);
          acc1 = __SMLAD(x1, c0, acc1);
          acc2 = __SMLAD(x3, c0, acc2);
          acc3 = __SMLAD(x2, c0, acc3);
  
          c0 = (*py);
          /* Read y[6] */
  #ifdef  ARM_MATH_BIG_ENDIAN
  
          c0 = c0 << 16u;
  #else
  
          c0 = c0 & 0x0000FFFF;
  #endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */
  
          /* Read x[10] */
  		b = *(px + 3);
  	
  #ifndef ARM_MATH_BIG_ENDIAN
  	
  		x3 = __PKHBT(a, b, 16);
  	
  #else
  	
  		x3 = __PKHBT(b, a, 16);
  	
  #endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/
  
  		px += 3u;
  
          /* Perform the multiply-accumulates */
          acc0 = __SMLADX(x1, c0, acc0);
          acc1 = __SMLAD(x2, c0, acc1);
          acc2 = __SMLADX(x2, c0, acc2);
          acc3 = __SMLADX(x3, c0, acc3);
        }
  
        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (acc0 >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;
  
        *pOut = (q15_t) (acc1 >> 15);
        pOut += inc;
  
        *pOut = (q15_t) (acc2 >> 15);
        pOut += inc;
  
        *pOut = (q15_t) (acc3 >> 15);
        pOut += inc;
  
        /* Increment the pointer pIn1 index, count by 1 */
        count += 4u;
  
        /* Update the inputA and inputB pointers for next MAC calculation */
        px = pIn1 + count;
        py = pIn2;
  
  
        /* Decrement the loop counter */
        blkCnt--;
      }
  
      /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
       ** No loop unrolling is used. */
      blkCnt = blockSize2 % 0x4u;
  
      while(blkCnt > 0u)
      {
        /* Accumulator is made zero for every iteration */
        sum = 0;
  
        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = srcBLen >> 2u;
  
        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
          /* Perform the multiply-accumulates */
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
  
          /* Decrement the loop counter */
          k--;
        }
  
        /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = srcBLen % 0x4u;
  
        while(k > 0u)
        {
          /* Perform the multiply-accumulates */
          sum += ((q31_t) * px++ * *py++);
  
          /* Decrement the loop counter */
          k--;
        }
  
        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;
  
        /* Increment the pointer pIn1 index, count by 1 */
        count++;
  
        /* Update the inputA and inputB pointers for next MAC calculation */
        px = pIn1 + count;
        py = pIn2;
  
        /* Decrement the loop counter */
        blkCnt--;
      }
    }
    else
    {
      /* If the srcBLen is not a multiple of 4,
       * the blockSize2 loop cannot be unrolled by 4 */
      blkCnt = blockSize2;
  
      while(blkCnt > 0u)
      {
        /* Accumulator is made zero for every iteration */
        sum = 0;
  
        /* Loop over srcBLen */
        k = srcBLen;
  
        while(k > 0u)
        {
          /* Perform the multiply-accumulate */
          sum += ((q31_t) * px++ * *py++);
  
          /* Decrement the loop counter */
          k--;
        }
  
        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;
  
        /* Increment the MAC count */
        count++;
  
        /* Update the inputA and inputB pointers for next MAC calculation */
        px = pIn1 + count;
        py = pIn2;
  
        /* Decrement the loop counter */
        blkCnt--;
      }
    }
  
    /* --------------------------
     * Initializations of stage3
     * -------------------------*/
  
    /* sum += x[srcALen-srcBLen+1] * y[0] + x[srcALen-srcBLen+2] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * sum += x[srcALen-srcBLen+2] * y[0] + x[srcALen-srcBLen+3] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * ....
     * sum +=  x[srcALen-2] * y[0] + x[srcALen-1] * y[1]
     * sum +=  x[srcALen-1] * y[0]
     */
  
    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = srcBLen - 1u;
  
    /* Working pointer of inputA */
    pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
    px = pSrc1;
  
    /* Working pointer of inputB */
    py = pIn2;
  
    /* -------------------
     * Stage3 process
     * ------------------*/
  
    while(blockSize3 > 0u)
    {
      /* Accumulator is made zero for every iteration */
      sum = 0;
  
      /* Apply loop unrolling and compute 4 MACs simultaneously. */
      k = count >> 2u;
  
      /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
       ** a second loop below computes MACs for the remaining 1 to 3 samples. */
      while(k > 0u)
      {
        /* Perform the multiply-accumulates */
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
          sum += ((q31_t) * px++ * *py++);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* If the count is not a multiple of 4, compute any remaining MACs here.
       ** No loop unrolling is used. */
      k = count % 0x4u;
  
      while(k > 0u)
      {
        /* Perform the multiply-accumulates */
          sum += ((q31_t) * px++ * *py++);
  
        /* Decrement the loop counter */
        k--;
      }
  
      /* Store the result in the accumulator in the destination buffer. */
      *pOut = (q15_t) (sum >> 15);
      /* Destination pointer is updated according to the address modifier, inc */
      pOut += inc;
  
      /* Update the inputA and inputB pointers for next MAC calculation */
      px = ++pSrc1;
      py = pIn2;
  
      /* Decrement the MAC count */
      count--;
  
      /* Decrement the loop counter */
      blockSize3--;
    }
  
  #endif /*   #ifndef UNALIGNED_SUPPORT_DISABLE */
  
  }
  
  /**
   * @} end of Corr group
   */
  