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/* ----------------------------------------------------------------------    

* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    

*    

* $Date:        19. March 2015

* $Revision:    V.1.4.5  

*    

* Project:          CMSIS DSP Library    

* Title:                arm_std_f32.c    

*    

* Description:  Standard deviation of the elements of a floating-point vector.  

*    

* 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 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))  

 *  

 *         where, 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 length of the input vector    

 * @param[out]      *pResult standard deviation value returned here    

 * @return none.    

 *    

 */

void arm_std_f32(

  float32_t * pSrc,

  uint32_t blockSize,

  float32_t * pResult)

{

  float32_t sum = 0.0f;                          /* Temporary result storage */

  float32_t sumOfSquares = 0.0f;                 /* Sum of squares */

  float32_t in;                                  /* input value */

  uint32_t blkCnt;                               /* loop counter */

#ifndef ARM_MATH_CM0_FAMILY

  /* Run the below code for Cortex-M4 and Cortex-M3 */

  float32_t meanOfSquares, mean, squareOfMean;

        if(blockSize == 1)

        {

                *pResult = 0;

                return;

        }

  /*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[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */

    /* Compute Sum of squares of the input samples    

     * and then store the result in a temporary variable, sum. */

    in = *pSrc++;

    sum += in;

    sumOfSquares += in * in;

    in = *pSrc++;

    sum += in;

    sumOfSquares += in * in;

    in = *pSrc++;

    sum += in;

    sumOfSquares += in * in;

    in = *pSrc++;

    sum += in;

    sumOfSquares += in * in;

    /* 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;

  while(blkCnt > 0u)

  {

    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */

    /* Compute Sum of squares of the input samples    

     * and then store the result in a temporary variable, sum. */

    in = *pSrc++;

    sum += in;

    sumOfSquares += in * in;

    /* Decrement the loop counter */

    blkCnt--;

  }

  /* Compute Mean of squares of the input samples    

   * and then store the 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 then store the result to the destination */

  arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);

#else

  /* Run the below code for Cortex-M0 */

  float32_t squareOfSum;                         /* Square of Sum */

  float32_t var;                                 /* Temporary varaince storage */

        if(blockSize == 1)

        {

                *pResult = 0;

                return;

        }

  /* Loop over blockSize number of values */

  blkCnt = blockSize;

  while(blkCnt > 0u)

  {

    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */

    /* Compute Sum of squares of the input samples    

     * and then store the result in a temporary variable, sumOfSquares. */

    in = *pSrc++;

    sumOfSquares += in * in;

    /* C = (A[0] + A[1] + ... + A[blockSize-1]) */

    /* Compute Sum of the input samples    

     * and then store the result in a temporary variable, sum. */

    sum += in;

    /* Decrement the loop counter */

    blkCnt--;

  }

  /* Compute the square of sum */

  squareOfSum = ((sum * sum) / (float32_t) blockSize);

  /* Compute the variance */

  var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));

  /* Compute standard deviation and then store the result to the destination */

  arm_sqrt_f32(var, pResult);

#endif /* #ifndef ARM_MATH_CM0_FAMILY */

}

/**    

 * @} end of STD group    

 */