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/* ----------------------------------------------------------------------    
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* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
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*    
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* $Date:        19. March 2015
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* $Revision:    V.1.4.5  
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*    
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* Project:          CMSIS DSP Library    
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* Title:                arm_var_f32.c    
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*    
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* Description:  Variance of the elements of a floating-point vector.    
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*    
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* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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*  
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*   - Redistributions of source code must retain the above copyright
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*     notice, this list of conditions and the following disclaimer.
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*   - Redistributions in binary form must reproduce the above copyright
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*     notice, this list of conditions and the following disclaimer in
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*     the documentation and/or other materials provided with the
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*     distribution.
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*   - Neither the name of ARM LIMITED nor the names of its contributors
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*     may be used to endorse or promote products derived from this
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*     software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.  
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* ---------------------------------------------------------------------------- */
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#include "arm_math.h"
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/**    
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 * @ingroup groupStats    
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 */
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/**    
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 * @defgroup variance  Variance    
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 *    
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 * Calculates the variance of the elements in the input vector.    
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 * The underlying algorithm is used:    
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 *    
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 * <pre>    
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 *      Result = (sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1)  
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 *  
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 *         where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]  
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 *  
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 *                         sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]  
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 * </pre>  
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 *    
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 * There are separate functions for floating point, Q31, and Q15 data types.    
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 */
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/**    
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 * @addtogroup variance    
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 * @{    
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 */
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/**    
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 * @brief Variance of the elements of a floating-point vector.    
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 * @param[in]       *pSrc points to the input vector    
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 * @param[in]       blockSize length of the input vector    
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 * @param[out]      *pResult variance value returned here    
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 * @return none.    
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 *    
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 */
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void arm_var_f32(
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  float32_t * pSrc,
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  uint32_t blockSize,
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  float32_t * pResult)
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{
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  float32_t sum = 0.0f;                          /* Temporary result storage */
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  float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
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  float32_t in;                                  /* input value */
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  uint32_t blkCnt;                               /* loop counter */
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#ifndef ARM_MATH_CM0_FAMILY
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  /* Run the below code for Cortex-M4 and Cortex-M3 */
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  float32_t meanOfSquares, mean, squareOfMean;   /* Temporary variables */
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        if(blockSize == 1)
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        {
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                *pResult = 0;
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                return;
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        }
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  /*loop Unrolling */
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  blkCnt = blockSize >> 2u;
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  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.    
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   ** a second loop below computes the remaining 1 to 3 samples. */
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  while(blkCnt > 0u)
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  {
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    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
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    /* Compute Sum of squares of the input samples    
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     * and then store the result in a temporary variable, sum. */
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    in = *pSrc++;
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    sum += in;
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    sumOfSquares += in * in;
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    in = *pSrc++;
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    sum += in;
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    sumOfSquares += in * in;
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    in = *pSrc++;
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    sum += in;
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    sumOfSquares += in * in;
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    in = *pSrc++;
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    sum += in;
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    sumOfSquares += in * in;
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    /* Decrement the loop counter */
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    blkCnt--;
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  }
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  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
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   ** No loop unrolling is used. */
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  blkCnt = blockSize % 0x4u;
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  while(blkCnt > 0u)
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  {
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    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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    /* Compute Sum of squares of the input samples    
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     * and then store the result in a temporary variable, sum. */
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    in = *pSrc++;
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    sum += in;
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    sumOfSquares += in * in;
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    /* Decrement the loop counter */
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    blkCnt--;
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  }
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  /* Compute Mean of squares of the input samples    
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   * and then store the result in a temporary variable, meanOfSquares. */
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  meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
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  /* Compute mean of all input values */
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  mean = sum / (float32_t) blockSize;
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  /* Compute square of mean */
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  squareOfMean = (mean * mean) * (((float32_t) blockSize) /
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                                  ((float32_t) blockSize - 1.0f));
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  /* Compute variance and then store the result to the destination */
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  *pResult = meanOfSquares - squareOfMean;
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#else
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  /* Run the below code for Cortex-M0 */
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  float32_t squareOfSum;                         /* Square of Sum */
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        if(blockSize == 1)
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        {
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                *pResult = 0;
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                return;
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        }
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  /* Loop over blockSize number of values */
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  blkCnt = blockSize;
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  while(blkCnt > 0u)
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  {
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    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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    /* Compute Sum of squares of the input samples    
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     * and then store the result in a temporary variable, sumOfSquares. */
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    in = *pSrc++;
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    sumOfSquares += in * in;
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    /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
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    /* Compute Sum of the input samples    
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     * and then store the result in a temporary variable, sum. */
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    sum += in;
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    /* Decrement the loop counter */
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    blkCnt--;
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  }
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  /* Compute the square of sum */
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  squareOfSum = ((sum * sum) / (float32_t) blockSize);
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  /* Compute the variance */
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  *pResult = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
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#endif /* #ifndef ARM_MATH_CM0_FAMILY */
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}
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/**    
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 * @} end of variance group    
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 */