tmk_core/tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/StatisticsFunctions/arm_var_f32.c

   1 /* ----------------------------------------------------------------------
   2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
   3 *
   4 * $Date:        17. January 2013
   5 * $Revision:    V1.4.1
   6 *
   7 * Project:          CMSIS DSP Library
   8 * Title:                arm_var_f32.c
   9 *
  10 * Description:  Variance of the elements of a floating-point vector.
  11 *
  12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  13 *
  14 * Redistribution and use in source and binary forms, with or without
  15 * modification, are permitted provided that the following conditions
  16 * are met:
  17 *   - Redistributions of source code must retain the above copyright
  18 *     notice, this list of conditions and the following disclaimer.
  19 *   - Redistributions in binary form must reproduce the above copyright
  20 *     notice, this list of conditions and the following disclaimer in
  21 *     the documentation and/or other materials provided with the
  22 *     distribution.
  23 *   - Neither the name of ARM LIMITED nor the names of its contributors
  24 *     may be used to endorse or promote products derived from this
  25 *     software without specific prior written permission.
  26 *
  27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  38 * POSSIBILITY OF SUCH DAMAGE.
  39 * ---------------------------------------------------------------------------- */
  40
  41 #include "arm_math.h"
  42
  43 /**
  44  * @ingroup groupStats
  45  */
  46
  47 /**
  48  * @defgroup variance  Variance
  49  *
  50  * Calculates the variance of the elements in the input vector.
  51  * The underlying algorithm is used:
  52  *
  53  * <pre>
  54  *      Result = (sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1)
  55  *
  56  *         where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
  57  *
  58  *                         sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
  59  * </pre>
  60  *
  61  * There are separate functions for floating point, Q31, and Q15 data types.
  62  */
  63
  64 /**
  65  * @addtogroup variance
  66  * @{
  67  */
  68
  69
  70 /**
  71  * @brief Variance of the elements of a floating-point vector.
  72  * @param[in]       *pSrc points to the input vector
  73  * @param[in]       blockSize length of the input vector
  74  * @param[out]      *pResult variance value returned here
  75  * @return none.
  76  *
  77  */
  78
  79
  80 void arm_var_f32(
  81   float32_t * pSrc,
  82   uint32_t blockSize,
  83   float32_t * pResult)
  84 {
  85
  86   float32_t sum = 0.0f;                          /* Temporary result storage */
  87   float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
  88   float32_t in;                                  /* input value */
  89   uint32_t blkCnt;                               /* loop counter */
  90
  91 #ifndef ARM_MATH_CM0_FAMILY
  92
  93   /* Run the below code for Cortex-M4 and Cortex-M3 */
  94
  95   float32_t meanOfSquares, mean, squareOfMean;   /* Temporary variables */
  96
  97   /*loop Unrolling */
  98   blkCnt = blockSize >> 2u;
  99
 100   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
 101    ** a second loop below computes the remaining 1 to 3 samples. */
 102   while(blkCnt > 0u)
 103   {
 104     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
 105     /* Compute Sum of squares of the input samples
 106      * and then store the result in a temporary variable, sum. */
 107     in = *pSrc++;
 108     sum += in;
 109     sumOfSquares += in * in;
 110     in = *pSrc++;
 111     sum += in;
 112     sumOfSquares += in * in;
 113     in = *pSrc++;
 114     sum += in;
 115     sumOfSquares += in * in;
 116     in = *pSrc++;
 117     sum += in;
 118     sumOfSquares += in * in;
 119
 120     /* Decrement the loop counter */
 121     blkCnt--;
 122   }
 123
 124   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
 125    ** No loop unrolling is used. */
 126   blkCnt = blockSize % 0x4u;
 127
 128   while(blkCnt > 0u)
 129   {
 130     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
 131     /* Compute Sum of squares of the input samples
 132      * and then store the result in a temporary variable, sum. */
 133     in = *pSrc++;
 134     sum += in;
 135     sumOfSquares += in * in;
 136
 137     /* Decrement the loop counter */
 138     blkCnt--;
 139   }
 140
 141   /* Compute Mean of squares of the input samples
 142    * and then store the result in a temporary variable, meanOfSquares. */
 143   meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
 144
 145   /* Compute mean of all input values */
 146   mean = sum / (float32_t) blockSize;
 147
 148   /* Compute square of mean */
 149   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
 150                                   ((float32_t) blockSize - 1.0f));
 151
 152   /* Compute variance and then store the result to the destination */
 153   *pResult = meanOfSquares - squareOfMean;
 154
 155 #else
 156
 157   /* Run the below code for Cortex-M0 */
 158   float32_t squareOfSum;                         /* Square of Sum */
 159
 160   /* Loop over blockSize number of values */
 161   blkCnt = blockSize;
 162
 163   while(blkCnt > 0u)
 164   {
 165     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
 166     /* Compute Sum of squares of the input samples
 167      * and then store the result in a temporary variable, sumOfSquares. */
 168     in = *pSrc++;
 169     sumOfSquares += in * in;
 170
 171     /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
 172     /* Compute Sum of the input samples
 173      * and then store the result in a temporary variable, sum. */
 174     sum += in;
 175
 176     /* Decrement the loop counter */
 177     blkCnt--;
 178   }
 179
 180   /* Compute the square of sum */
 181   squareOfSum = ((sum * sum) / (float32_t) blockSize);
 182
 183   /* Compute the variance */
 184   *pResult = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
 185
 186 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
 187
 188 }
 189
 190 /**
 191  * @} end of variance group
 192  */