CMSIS-DSP/Source/StatisticsFunctions/arm_var_f16.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_var_f16.c
 * Description:  Variance of the elements of a floating-point vector
 *
 * $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/statistics_functions_f16.h"


#if defined(ARM_FLOAT16_SUPPORTED)


/**
  @ingroup groupStats
 */


/**
  @addtogroup variance
  @{
 */

/**
  @brief         Variance of the elements of a floating-point vector.
  @param[in]     pSrc       points to the input vector
  @param[in]     blockSize  number of samples in input vector
  @param[out]    pResult    variance value returned here
 */
#if defined(ARM_MATH_MVE_FLOAT16) && !defined(ARM_MATH_AUTOVECTORIZE)

#include "arm_helium_utils.h"


void arm_var_f16(
           const float16_t * pSrc,
                 uint32_t blockSize,
                 float16_t * pResult)
{
    int32_t         blkCnt;     /* loop counters */
    f16x8_t         vecSrc;
    f16x8_t         sumVec = vdupq_n_f16(0.0f16);
    float16_t       fMean;

    if (blockSize <= 1U) {
        *pResult = 0;
        return;
    }


    arm_mean_f16(pSrc, blockSize, &fMean);

    blkCnt = blockSize;
    do {
        mve_pred16_t    p = vctp16q(blkCnt);

        vecSrc = vldrhq_z_f16((float16_t const *) pSrc, p);
        /*
         * sum lanes
         */
        vecSrc = vsubq_m(vuninitializedq_f16(), vecSrc, fMean, p);
        sumVec = vfmaq_m(sumVec, vecSrc, vecSrc, p);

        blkCnt -= 8;
        pSrc += 8;
    }
    while (blkCnt > 0);
    
    /* Variance */
    *pResult = (_Float16)vecAddAcrossF16Mve(sumVec) / (_Float16) (blockSize - 1.0f16);
}
#else

void arm_var_f16(
  const float16_t * pSrc,
        uint32_t blockSize,
        float16_t * pResult)
{
        uint32_t blkCnt;                               /* Loop counter */
        _Float16 sum = 0.0f;                          /* Temporary result storage */
        _Float16 fSum = 0.0f;
        _Float16 fMean, fValue;
  const float16_t * pInput = pSrc;

  if (blockSize <= 1U)
  {
    *pResult = 0;
    return;
  }

#if defined (ARM_MATH_LOOPUNROLL) && !defined(ARM_MATH_AUTOVECTORIZE)

  /* Loop unrolling: Compute 4 outputs at a time */
  blkCnt = blockSize >> 2U;

  while (blkCnt > 0U)
  {
    /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */

    sum += (_Float16)*pInput++;
    sum += (_Float16)*pInput++;
    sum += (_Float16)*pInput++;
    sum += (_Float16)*pInput++;


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

  /* Loop unrolling: Compute remaining outputs */
  blkCnt = blockSize % 0x4U;

#else

  /* Initialize blkCnt with number of samples */
  blkCnt = blockSize;

#endif /* #if defined (ARM_MATH_LOOPUNROLL) */

  while (blkCnt > 0U)
  {
    /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */

    sum += (_Float16)*pInput++;

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

  /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize  */
  fMean = (_Float16)sum / (_Float16) blockSize;

  pInput = pSrc;

#if defined (ARM_MATH_LOOPUNROLL) && !defined(ARM_MATH_AUTOVECTORIZE)

  /* Loop unrolling: Compute 4 outputs at a time */
  blkCnt = blockSize >> 2U;

  while (blkCnt > 0U)
  {
    fValue = (_Float16)*pInput++ - (_Float16)fMean;
    fSum += (_Float16)fValue * (_Float16)fValue;

    fValue = (_Float16)*pInput++ - (_Float16)fMean;
    fSum += (_Float16)fValue * (_Float16)fValue;

    fValue = (_Float16)*pInput++ - (_Float16)fMean;
    fSum += (_Float16)fValue * (_Float16)fValue;

    fValue = (_Float16)*pInput++ - (_Float16)fMean;
    fSum += (_Float16)fValue * (_Float16)fValue;

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

  /* Loop unrolling: Compute remaining outputs */
  blkCnt = blockSize % 0x4U;

#else

  /* Initialize blkCnt with number of samples */
  blkCnt = blockSize;

#endif /* #if defined (ARM_MATH_LOOPUNROLL) */

  while (blkCnt > 0U)
  {
    fValue = (_Float16)*pInput++ - (_Float16)fMean;
    fSum += (_Float16)fValue * (_Float16)fValue;

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

  /* Variance */
  *pResult = (_Float16)fSum / ((_Float16)blockSize - 1.0f16);
}
#endif /* defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) */

/**
  @} end of variance group
 */

#endif /* #if defined(ARM_FLOAT16_SUPPORTED) */