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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_var_f32.c
* Description: Variance of the elements of a floating-point vector
*
* $Date: 27. January 2017
* $Revision: V.1.5.1
*
* Target Processor: Cortex-M cores
* -------------------------------------------------------------------- */
/*
* Copyright (C) 2010-2017 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 "arm_math.h"
/**
* @ingroup groupStats
*/
/**
* @defgroup variance Variance
*
* Calculates the variance of the elements in the input vector.
* The underlying algorithm used is the direct method sometimes referred to as the two-pass method:
*
* <pre>
* Result = sum(element - meanOfElements)^2) / numElement - 1
*
* where, meanOfElements = ( pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] ) / blockSize
*
* </pre>
*
* There are separate functions for floating point, Q31, and Q15 data types.
*/
/**
* @addtogroup variance
* @{
*/
/**
* @brief Variance of the elements of a floating-point vector.
* @param[in] *pSrc points to the input vector
* @param[in] blockSize length of the input vector
* @param[out] *pResult variance value returned here
* @return none.
*/
void arm_var_f32(
float32_t * pSrc,
uint32_t blockSize,
float32_t * pResult)
{
float32_t fMean, fValue;
uint32_t blkCnt; /* loop counter */
float32_t * pInput = pSrc;
float32_t sum = 0.0f;
float32_t fSum = 0.0f;
#if defined(ARM_MATH_DSP)
float32_t in1, in2, in3, in4;
#endif
if (blockSize <= 1U)
{
*pResult = 0;
return;
}
#if defined(ARM_MATH_DSP)
/* Run the below code for Cortex-M4 and Cortex-M7 */
/*loop Unrolling */
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)
{
/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
in1 = *pInput++;
in2 = *pInput++;
in3 = *pInput++;
in4 = *pInput++;
sum += in1;
sum += in2;
sum += in3;
sum += in4;
/* Decrement the loop counter */
blkCnt--;
}
/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
** No loop unrolling is used. */
blkCnt = blockSize % 0x4U;
#else
/* Run the below code for Cortex-M0 or Cortex-M3 */
/* Loop over blockSize number of values */
blkCnt = blockSize;
#endif
while (blkCnt > 0U)
{
/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
sum += *pInput++;
/* Decrement the loop counter */
blkCnt--;
}
/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize */
fMean = sum / (float32_t) blockSize;
pInput = pSrc;
#if defined(ARM_MATH_DSP)
/*loop Unrolling */
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)
{
fValue = *pInput++ - fMean;
fSum += fValue * fValue;
fValue = *pInput++ - fMean;
fSum += fValue * fValue;
fValue = *pInput++ - fMean;
fSum += fValue * fValue;
fValue = *pInput++ - fMean;
fSum += fValue * fValue;
/* Decrement the loop counter */
blkCnt--;
}
blkCnt = blockSize % 0x4U;
#else
/* Run the below code for Cortex-M0 or Cortex-M3 */
/* Loop over blockSize number of values */
blkCnt = blockSize;
#endif
while (blkCnt > 0U)
{
fValue = *pInput++ - fMean;
fSum += fValue * fValue;
/* Decrement the loop counter */
blkCnt--;
}
/* Variance */
*pResult = fSum / (float32_t)(blockSize - 1.0f);
}
/**
* @} end of variance group
*/
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