tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/StatisticsFunctions/arm_std_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_std_f32.c
   9 *
  10 * Description:  Standard deviation 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 STD Standard deviation
  49  *
  50  * Calculates the standard deviation of the elements in the input vector.
  51  * The underlying algorithm is used:
  52  *
  53  * <pre>
  54  *      Result = sqrt((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 STD
  66  * @{
  67  */
  68
  69
  70 /**
  71  * @brief Standard deviation 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 standard deviation value returned here
  75  * @return none.
  76  *
  77  */
  78
  79
  80 void arm_std_f32(
  81   float32_t * pSrc,
  82   uint32_t blockSize,
  83   float32_t * pResult)
  84 {
  85   float32_t sum = 0.0f;                          /* Temporary result storage */
  86   float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
  87   float32_t in;                                  /* input value */
  88   uint32_t blkCnt;                               /* loop counter */
  89
  90 #ifndef ARM_MATH_CM0_FAMILY
  91
  92   /* Run the below code for Cortex-M4 and Cortex-M3 */
  93
  94   float32_t meanOfSquares, mean, squareOfMean;
  95
  96   /*loop Unrolling */
  97   blkCnt = blockSize >> 2u;
  98
  99   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
 100    ** a second loop below computes the remaining 1 to 3 samples. */
 101   while(blkCnt > 0u)
 102   {
 103     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
 104     /* Compute Sum of squares of the input samples
 105      * and then store the result in a temporary variable, sum. */
 106     in = *pSrc++;
 107     sum += in;
 108     sumOfSquares += in * in;
 109     in = *pSrc++;
 110     sum += in;
 111     sumOfSquares += in * in;
 112     in = *pSrc++;
 113     sum += in;
 114     sumOfSquares += in * in;
 115     in = *pSrc++;
 116     sum += in;
 117     sumOfSquares += in * in;
 118
 119     /* Decrement the loop counter */
 120     blkCnt--;
 121   }
 122
 123   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
 124    ** No loop unrolling is used. */
 125   blkCnt = blockSize % 0x4u;
 126
 127   while(blkCnt > 0u)
 128   {
 129     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
 130     /* Compute Sum of squares of the input samples
 131      * and then store the result in a temporary variable, sum. */
 132     in = *pSrc++;
 133     sum += in;
 134     sumOfSquares += in * in;
 135
 136     /* Decrement the loop counter */
 137     blkCnt--;
 138   }
 139
 140   /* Compute Mean of squares of the input samples
 141    * and then store the result in a temporary variable, meanOfSquares. */
 142   meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
 143
 144   /* Compute mean of all input values */
 145   mean = sum / (float32_t) blockSize;
 146
 147   /* Compute square of mean */
 148   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
 149                                   ((float32_t) blockSize - 1.0f));
 150
 151   /* Compute standard deviation and then store the result to the destination */
 152   arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
 153
 154 #else
 155
 156   /* Run the below code for Cortex-M0 */
 157
 158   float32_t squareOfSum;                         /* Square of Sum */
 159   float32_t var;                                 /* Temporary varaince storage */
 160
 161   /* Loop over blockSize number of values */
 162   blkCnt = blockSize;
 163
 164   while(blkCnt > 0u)
 165   {
 166     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
 167     /* Compute Sum of squares of the input samples
 168      * and then store the result in a temporary variable, sumOfSquares. */
 169     in = *pSrc++;
 170     sumOfSquares += in * in;
 171
 172     /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
 173     /* Compute Sum of the input samples
 174      * and then store the result in a temporary variable, sum. */
 175     sum += in;
 176
 177     /* Decrement the loop counter */
 178     blkCnt--;
 179   }
 180
 181   /* Compute the square of sum */
 182   squareOfSum = ((sum * sum) / (float32_t) blockSize);
 183
 184   /* Compute the variance */
 185   var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
 186
 187   /* Compute standard deviation and then store the result to the destination */
 188   arm_sqrt_f32(var, pResult);
 189
 190 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
 191
 192 }
 193
 194 /**
 195  * @} end of STD group
 196  */