text: /* ----------------------------------------------------------------------
  * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
  *
  * $Date: 16/10/14 6:01p $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
   */
  