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/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_correlate_q7.c
 * Description:  Correlation of Q7 sequences
 *
 * $Date:        23 April 2021
 * $Revision:    V1.9.0
 *
 * Target Processor: Cortex-M and Cortex-A cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

//#include "dsp/filtering_functions.h"
#define int32_t int
#define uint32_t unsigned int
#define uint16_t unsigned short
#define q7_t signed char
#define q15_t signed short
#define q31_t signed int
#define __STATIC_FORCEINLINE static inline __attribute__((always_inline))

__STATIC_FORCEINLINE int32_t __SSAT(int32_t val, uint32_t sat)
{
  if ((sat >= 1U) && (sat <= 32U))
  {
    const int32_t max = (int32_t)((1U << (sat - 1U)) - 1U);
    const int32_t min = -1 - max ;
    if (val > max)
    {
      return max;
    }
    else if (val < min)
    {
      return min;
    }
  }
  return val;
}

/**
  @ingroup groupFilters
 */

/**
  @addtogroup Corr
  @{
 */

/**
  @brief         Correlation of Q7 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

@par           Scaling and Overflow Behavior
                   The function is implemented using a 32-bit internal accumulator.
                   Both the inputs are represented in 1.7 format and multiplications yield a 2.14 result.
                   The 2.14 intermediate results are accumulated in a 32-bit accumulator in 18.14 format.
                   This approach provides 17 guard bits and there is no risk of overflow as long as <code>max(srcALen, srcBLen)<131072</code>.
                   The 18.14 result is then truncated to 18.7 format by discarding the low 7 bits and saturated to 1.7 format.

@remark
                   Refer to \ref arm_correlate_opt_q7() for a faster implementation of this function.
 */
void arm_correlate_q7(
  const q7_t * pSrcA,
        uint32_t srcALen,
  const q7_t * pSrcB,
        uint32_t srcBLen,
        q7_t * pDst)
{

const q7_t *pIn1;                                    /* InputA pointer */
  const q7_t *pIn2;                                    /* InputB pointer */
        q7_t *pOut = pDst;                             /* Output pointer */
  const q7_t *px;                                      /* Intermediate inputA pointer */
  const q7_t *py;                                      /* Intermediate inputB pointer */
  const q7_t *pSrc1;                                   /* Intermediate pointers */
        q31_t sum;                                     /* Accumulators */
        uint32_t blockSize1, blockSize2, blockSize3;   /* Loop counters */
        uint32_t j, k, count, blkCnt;                  /* Loop counters */
        uint32_t outBlockSize;
        int32_t inc = 1;

/* 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 stages according to the number of multiplications that has to be
   * taken place between inputA samples and inputB samples. In the first stage of the
   * algorithm, the multiplications increase by one for every iteration.
   * In the second stage of the algorithm, srcBLen number of multiplications are done.
   * In the third stage 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 stage starts here */
  while (blockSize1 > 0U)
  {
    /* Accumulator is made zero for every iteration */
    sum = 0;

/* Initialize k with number of samples */
    k = count;

while (k > 0U)
    {
      /* Perform the multiply-accumulate */
      /* x[0] * y[srcBLen - 1] */
      sum += (q31_t) ((q15_t) *px++ * *py++);

/* Decrement loop counter */
      k--;
    }

/* Store the result in the accumulator in the destination buffer. */
    *pOut = (q7_t) (__SSAT(sum >> 7U, 8));
    /* 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 MAC count */
    count++;

/* Decrement 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 */
  if (srcBLen >= 4U)
  {
    /* Initialize blkCnt with number of samples */
    blkCnt = blockSize2;

while (blkCnt > 0U)
    {
      /* Accumulator is made zero for every iteration */
      sum = 0;

/* Initialize blkCnt with number of samples */
      k = srcBLen;

while (k > 0U)
      {
        /* Perform the multiply-accumulate */
        sum += ((q15_t) *px++ * *py++);

/* Decrement the loop counter */
        k--;
      }

/* Store the result in the accumulator in the destination buffer. */
      *pOut = (q7_t) (__SSAT(sum >> 7U, 8));
      /* 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;

/* srcBLen number of MACS should be performed */
      k = srcBLen;

while (k > 0U)
      {
        /* Perform the multiply-accumulate */
        sum += ((q15_t) *px++ * *py++);

/* Decrement the loop counter */
        k--;
      }

/* Store the result in the accumulator in the destination buffer. */
      *pOut = (q7_t) (__SSAT(sum >> 7U, 8));
      /* 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 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;

/* Initialize blkCnt with number of samples */
    k = count;

while (k > 0U)
    {
      /* Perform the multiply-accumulate */
      sum += ((q15_t) *px++ * *py++);

/* Decrement loop counter */
      k--;
    }

/* Update the inputA and inputB pointers for next MAC calculation */
    px = ++pSrc1;
    py = pIn2;

/* Decrement MAC count */
    count--;

/* Decrement loop counter */
    blockSize3--;
  }

}

/**
  @} end of Corr group
 */