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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_std_f32.c
* Description: Standard deviation of the elements of a floating-point vector
*
* $Date: 18. March 2019
* $Revision: V1.6.0
*
* Target Processor: Cortex-M cores
* -------------------------------------------------------------------- */
/*
* Copyright (C) 2010-2019 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 STD Standard deviation
Calculates the standard deviation of the elements in the input vector.
The underlying algorithm is used:
<pre>
Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1))
sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
</pre>
There are separate functions for floating point, Q31, and Q15 data types.
*/
/**
@addtogroup STD
@{
*/
/**
@brief Standard deviation 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 standard deviation value returned here
@return none
*/
#if defined(ARM_MATH_NEON_EXPERIMENTAL)
void arm_std_f32(
const float32_t * pSrc,
uint32_t blockSize,
float32_t * pResult)
{
float32_t var;
arm_var_f32(pSrc,blockSize,&var);
arm_sqrt_f32(var, pResult);
}
#else
void arm_std_f32(
const float32_t * pSrc,
uint32_t blockSize,
float32_t * pResult)
{
uint32_t blkCnt; /* Loop counter */
float32_t sum = 0.0f; /* Temporary result storage */
float32_t sumOfSquares = 0.0f; /* Sum of squares */
float32_t in; /* Temporary variable to store input value */
#ifndef ARM_MATH_CM0_FAMILY
float32_t meanOfSquares, mean, squareOfMean; /* Temporary variables */
#else
float32_t squareOfSum; /* Square of Sum */
float32_t var; /* Temporary varaince storage */
#endif
if (blockSize <= 1U)
{
*pResult = 0;
return;
}
#if defined (ARM_MATH_LOOPUNROLL)
/* Loop unrolling: Compute 4 outputs at a time */
blkCnt = blockSize >> 2U;
while (blkCnt > 0U)
{
/* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
/* C = A[0] + A[1] + ... + A[blockSize-1] */
in = *pSrc++;
/* Compute sum of squares and store result in a temporary variable, sumOfSquares. */
sumOfSquares += in * in;
/* Compute sum and store result in a temporary variable, sum. */
sum += in;
in = *pSrc++;
sumOfSquares += in * in;
sum += in;
in = *pSrc++;
sumOfSquares += in * in;
sum += in;
in = *pSrc++;
sumOfSquares += in * in;
sum += in;
/* 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[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
/* C = A[0] + A[1] + ... + A[blockSize-1] */
in = *pSrc++;
/* Compute sum of squares and store result in a temporary variable, sumOfSquares. */
sumOfSquares += ( in * in);
/* Compute sum and store result in a temporary variable, sum. */
sum += in;
/* Decrement loop counter */
blkCnt--;
}
#ifndef ARM_MATH_CM0_FAMILY
/* Compute Mean of squares and store result in a temporary variable, meanOfSquares. */
meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
/* Compute mean of all input values */
mean = sum / (float32_t) blockSize;
/* Compute square of mean */
squareOfMean = (mean * mean) * (((float32_t) blockSize) /
((float32_t) blockSize - 1.0f));
/* Compute standard deviation and store result to destination */
arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
#else
/* Run the below code for Cortex-M0 */
/* Compute square of sum */
squareOfSum = ((sum * sum) / (float32_t) blockSize);
/* Compute variance */
var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
/* Compute standard deviation and store result in destination */
arm_sqrt_f32(var, pResult);
#endif /* #ifndef ARM_MATH_CM0_FAMILY */
}
#endif /* #if defined(ARM_MATH_NEON) */
/**
@} end of STD group
*/
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