Diff: FilteringFunctions/arm_correlate_q15.c

Revision:

0:3d9c67d97d6f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/FilteringFunctions/arm_correlate_q15.c	Mon Jul 28 15:03:15 2014 +0000
@@ -0,0 +1,719 @@
+/* ----------------------------------------------------------------------   
+* Copyright (C) 2010-2014 ARM Limited. All rights reserved.   
+*   
+* $Date:        12. March 2014
+* $Revision: 	V1.4.3
+*   
+* Project: 	    CMSIS DSP Library   
+* Title:		arm_correlate_q15.c   
+*   
+* Description:	Correlation of Q15 sequences. 
+*   
+* 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 Corr   
+ * @{   
+ */
+
+/**   
+ * @brief Correlation of Q15 sequences. 
+ * @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.   
+ *   
+ * @details   
+ * <b>Scaling and Overflow Behavior:</b>   
+ *   
+ * \par   
+ * The function is implemented using a 64-bit internal accumulator.   
+ * Both inputs are in 1.15 format and multiplications yield a 2.30 result.   
+ * The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format.   
+ * This approach provides 33 guard bits and there is no risk of overflow.   
+ * The 34.30 result is then truncated to 34.15 format by discarding the low 15 bits and then saturated to 1.15 format.   
+ *   
+ * \par   
+ * Refer to <code>arm_correlate_fast_q15()</code> for a faster but less precise version of this function for Cortex-M3 and Cortex-M4. 
+ *
+ * \par    
+ * Refer the function <code>arm_correlate_opt_q15()</code> for a faster implementation of this function using scratch buffers.
+ * 
+ */
+
+void arm_correlate_q15(
+  q15_t * pSrcA,
+  uint32_t srcALen,
+  q15_t * pSrcB,
+  uint32_t srcBLen,
+  q15_t * pDst)
+{
+
+#if (defined(ARM_MATH_CM4) || defined(ARM_MATH_CM3)) && !defined(UNALIGNED_SUPPORT_DISABLE)
+
+  /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+  q15_t *pIn1;                                   /* inputA pointer               */
+  q15_t *pIn2;                                   /* inputB pointer               */
+  q15_t *pOut = pDst;                            /* output pointer               */
+  q63_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 = __SMLALD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
+      /* x[3] * y[srcBLen - 1] , x[2] * y[srcBLen - 2] */
+      sum = __SMLALD(*__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 = __SMLALD(*px++, *py++, sum);
+
+      /* Decrement the loop counter */
+      k--;
+    }
+
+    /* Store the result in the accumulator in the destination buffer. */
+    *pOut = (q15_t) (__SSAT((sum >> 15), 16));
+    /* 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 = __SMLALD(x0, c0, acc0);
+
+        /* acc1 +=  x[1] * y[0] + x[2] * y[1] */
+        acc1 = __SMLALD(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 = __SMLALD(x2, c0, acc2);
+
+        /* acc3 +=  x[3] * y[0] + x[4] * y[1] */
+        acc3 = __SMLALD(x3, c0, acc3);
+
+        /* Read y[2] and y[3] */
+        c0 = *__SIMD32(py)++;
+
+        /* acc0 +=  x[2] * y[2] + x[3] * y[3] */
+        acc0 = __SMLALD(x2, c0, acc0);
+
+        /* acc1 +=  x[3] * y[2] + x[4] * y[3] */
+        acc1 = __SMLALD(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 = __SMLALD(x0, c0, acc2);
+
+        /* acc3 +=  x[5] * y[2] + x[6] * y[3] */
+        acc3 = __SMLALD(x1, c0, acc3);
+
+      } while(--k);
+
+      /* 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 = __SMLALD(x0, c0, acc0);
+        acc1 = __SMLALD(x1, c0, acc1);
+        acc2 = __SMLALDX(x1, c0, acc2);
+        acc3 = __SMLALDX(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 = __SMLALD(x0, c0, acc0);
+        acc1 = __SMLALD(x1, c0, acc1);
+        acc2 = __SMLALD(x3, c0, acc2);
+        acc3 = __SMLALD(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 = __SMLALD(x0, c0, acc0);
+        acc1 = __SMLALD(x1, c0, acc1);
+        acc2 = __SMLALD(x3, c0, acc2);
+        acc3 = __SMLALD(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 = __SMLALDX(x1, c0, acc0);
+        acc1 = __SMLALD(x2, c0, acc1);
+        acc2 = __SMLALDX(x2, c0, acc2);
+        acc3 = __SMLALDX(x3, c0, acc3);
+      }
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut = (q15_t) (__SSAT(acc0 >> 15, 16));
+      /* Destination pointer is updated according to the address modifier, inc */
+      pOut += inc;
+
+      *pOut = (q15_t) (__SSAT(acc1 >> 15, 16));
+      pOut += inc;
+
+      *pOut = (q15_t) (__SSAT(acc2 >> 15, 16));
+      pOut += inc;
+
+      *pOut = (q15_t) (__SSAT(acc3 >> 15, 16));
+      pOut += inc;
+
+      /* Increment the count by 4 as 4 output values are computed */
+      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 += ((q63_t) * px++ * *py++);
+        sum += ((q63_t) * px++ * *py++);
+        sum += ((q63_t) * px++ * *py++);
+        sum += ((q63_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 += ((q63_t) * px++ * *py++);
+
+        /* Decrement the loop counter */
+        k--;
+      }
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut = (q15_t) (__SSAT(sum >> 15, 16));
+      /* Destination pointer is updated according to the address modifier, inc */
+      pOut += inc;
+
+      /* Increment count by 1, as one output value is computed */
+      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 += ((q63_t) * px++ * *py++);
+
+        /* Decrement the loop counter */
+        k--;
+      }
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut = (q15_t) (__SSAT(sum >> 15, 16));
+      /* 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 = __SMLALD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
+      /* sum += x[srcALen - srcBLen + 2] * y[1] , sum += x[srcALen - srcBLen + 1] * y[0] */
+      sum = __SMLALD(*__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 = __SMLALD(*px++, *py++, sum);
+
+      /* Decrement the loop counter */
+      k--;
+    }
+
+    /* Store the result in the accumulator in the destination buffer. */
+    *pOut = (q15_t) (__SSAT((sum >> 15), 16));
+    /* 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
+
+/* Run the below code for Cortex-M0 */
+
+  q15_t *pIn1 = pSrcA;                           /* inputA pointer               */
+  q15_t *pIn2 = pSrcB + (srcBLen - 1u);          /* inputB pointer               */
+  q63_t sum;                                     /* Accumulators                  */
+  uint32_t i = 0u, j;                            /* loop counters */
+  uint32_t inv = 0u;                             /* Reverse order flag */
+  uint32_t tot = 0u;                             /* Length */
+
+  /* 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 a varaible, inv is set to 1 */
+  /* If lengths are not equal then zero pad has to be done 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 */
+  /* Once the zero padding is done the remaining of the output is calcualted  
+   * using convolution but with the shorter signal time shifted. */
+
+  /* Calculate the length of the remaining sequence */
+  tot = ((srcALen + srcBLen) - 2u);
+
+  if(srcALen > srcBLen)
+  {
+    /* Calculating the number of zeros to be padded to the output */
+    j = srcALen - srcBLen;
+
+    /* Initialise the pointer after zero padding */
+    pDst += j;
+  }
+
+  else if(srcALen < srcBLen)
+  {
+    /* Initialization to inputB pointer */
+    pIn1 = pSrcB;
+
+    /* Initialization to the end of inputA pointer */
+    pIn2 = pSrcA + (srcALen - 1u);
+
+    /* Initialisation of the pointer after zero padding */
+    pDst = pDst + tot;
+
+    /* Swapping the lengths */
+    j = srcALen;
+    srcALen = srcBLen;
+    srcBLen = j;
+
+    /* Setting the reverse flag */
+    inv = 1;
+
+  }
+
+  /* Loop to calculate convolution for output length number of times */
+  for (i = 0u; i <= tot; i++)
+  {
+    /* Initialize sum with zero to carry on MAC operations */
+    sum = 0;
+
+    /* Loop to perform MAC operations according to convolution equation */
+    for (j = 0u; j <= i; j++)
+    {
+      /* Check the array limitations */
+      if((((i - j) < srcBLen) && (j < srcALen)))
+      {
+        /* z[i] += x[i-j] * y[j] */
+        sum += ((q31_t) pIn1[j] * pIn2[-((int32_t) i - j)]);
+      }
+    }
+    /* Store the output in the destination buffer */
+    if(inv == 1)
+      *pDst-- = (q15_t) __SSAT((sum >> 15u), 16u);
+    else
+      *pDst++ = (q15_t) __SSAT((sum >> 15u), 16u);
+  }
+
+#endif /*#if (defined(ARM_MATH_CM4) || defined(ARM_MATH_CM3)) && !defined(UNALIGNED_SUPPORT_DISABLE) */
+
+}
+
+/**   
+ * @} end of Corr group   
+ */