lib/main/CMSIS/DSP/Source/StatisticsFunctions/arm_std_f32.c

   1 /* ----------------------------------------------------------------------
   2  * Project:      CMSIS DSP Library
   3  * Title:        arm_std_f32.c
   4  * Description:  Standard deviation of the elements of a floating-point vector
   5  *
   6  * $Date:        27. January 2017
   7  * $Revision:    V.1.5.1
   8  *
   9  * Target Processor: Cortex-M cores
  10  * -------------------------------------------------------------------- */
  11 /*
  12  * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
  13  *
  14  * SPDX-License-Identifier: Apache-2.0
  15  *
  16  * Licensed under the Apache License, Version 2.0 (the License); you may
  17  * not use this file except in compliance with the License.
  18  * You may obtain a copy of the License at
  19  *
  20  * www.apache.org/licenses/LICENSE-2.0
  21  *
  22  * Unless required by applicable law or agreed to in writing, software
  23  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
  24  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  25  * See the License for the specific language governing permissions and
  26  * limitations under the License.
  27  */
  28
  29 #include "arm_math.h"
  30
  31 /**
  32  * @ingroup groupStats
  33  */
  34
  35 /**
  36  * @defgroup STD Standard deviation
  37  *
  38  * Calculates the standard deviation of the elements in the input vector.
  39  * The underlying algorithm is used:
  40  *
  41  * <pre>
  42  *   Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1))
  43  *
  44  *     where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
  45  *
  46  *                     sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
  47  * </pre>
  48  *
  49  * There are separate functions for floating point, Q31, and Q15 data types.
  50  */
  51
  52 /**
  53  * @addtogroup STD
  54  * @{
  55  */
  56
  57
  58 /**
  59  * @brief Standard deviation of the elements of a floating-point vector.
  60  * @param[in]       *pSrc points to the input vector
  61  * @param[in]       blockSize length of the input vector
  62  * @param[out]      *pResult standard deviation value returned here
  63  * @return none.
  64  */
  65
  66 void arm_std_f32(
  67   float32_t * pSrc,
  68   uint32_t blockSize,
  69   float32_t * pResult)
  70 {
  71   float32_t sum = 0.0f;                          /* Temporary result storage */
  72   float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
  73   float32_t in;                                  /* input value */
  74   uint32_t blkCnt;                               /* loop counter */
  75 #if defined (ARM_MATH_DSP)
  76   float32_t meanOfSquares, mean, squareOfMean;   /* Temporary variables */
  77 #else
  78   float32_t squareOfSum;                         /* Square of Sum */
  79   float32_t var;                                 /* Temporary varaince storage */
  80 #endif
  81
  82   if (blockSize == 1U)
  83   {
  84     *pResult = 0;
  85     return;
  86   }
  87
  88 #if defined (ARM_MATH_DSP)
  89   /* Run the below code for Cortex-M4 and Cortex-M3 */
  90
  91   /*loop Unrolling */
  92   blkCnt = blockSize >> 2U;
  93
  94   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  95    ** a second loop below computes the remaining 1 to 3 samples. */
  96   while (blkCnt > 0U)
  97   {
  98     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
  99     /* Compute Sum of squares of the input samples
 100      * and then store the result in a temporary variable, sum. */
 101     in = *pSrc++;
 102     sum += in;
 103     sumOfSquares += in * in;
 104     in = *pSrc++;
 105     sum += in;
 106     sumOfSquares += in * in;
 107     in = *pSrc++;
 108     sum += in;
 109     sumOfSquares += in * in;
 110     in = *pSrc++;
 111     sum += in;
 112     sumOfSquares += in * in;
 113
 114     /* Decrement the loop counter */
 115     blkCnt--;
 116   }
 117
 118   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
 119    ** No loop unrolling is used. */
 120   blkCnt = blockSize % 0x4U;
 121
 122   while (blkCnt > 0U)
 123   {
 124     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
 125     /* Compute Sum of squares of the input samples
 126      * and then store the result in a temporary variable, sum. */
 127     in = *pSrc++;
 128     sum += in;
 129     sumOfSquares += in * in;
 130
 131     /* Decrement the loop counter */
 132     blkCnt--;
 133   }
 134
 135   /* Compute Mean of squares of the input samples
 136    * and then store the result in a temporary variable, meanOfSquares. */
 137   meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
 138
 139   /* Compute mean of all input values */
 140   mean = sum / (float32_t) blockSize;
 141
 142   /* Compute square of mean */
 143   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
 144                                   ((float32_t) blockSize - 1.0f));
 145
 146   /* Compute standard deviation and then store the result to the destination */
 147   arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
 148
 149 #else
 150   /* Run the below code for Cortex-M0 */
 151
 152   /* Loop over blockSize number of values */
 153   blkCnt = blockSize;
 154
 155   while (blkCnt > 0U)
 156   {
 157     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
 158     /* Compute Sum of squares of the input samples
 159      * and then store the result in a temporary variable, sumOfSquares. */
 160     in = *pSrc++;
 161     sumOfSquares += in * in;
 162
 163     /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
 164     /* Compute Sum of the input samples
 165      * and then store the result in a temporary variable, sum. */
 166     sum += in;
 167
 168     /* Decrement the loop counter */
 169     blkCnt--;
 170   }
 171
 172   /* Compute the square of sum */
 173   squareOfSum = ((sum * sum) / (float32_t) blockSize);
 174
 175   /* Compute the variance */
 176   var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
 177
 178   /* Compute standard deviation and then store the result to the destination */
 179   arm_sqrt_f32(var, pResult);
 180
 181 #endif /* #if defined (ARM_MATH_DSP) */
 182 }
 183
 184 /**
 185  * @} end of STD group
 186  */