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  1. /* ----------------------------------------------------------------------
  2.  * Project:      CMSIS DSP Library
  3.  * Title:        arm_var_f32.c
  4.  * Description:  Variance 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 variance  Variance
  37.  *
  38.  * Calculates the variance of the elements in the input vector.
  39.  * The underlying algorithm used is the direct method sometimes referred to as the two-pass method:
  40.  *
  41.  * <pre>
  42.  *   Result = sum(element - meanOfElements)^2) / numElement - 1
  43.  *
  44.  *     where, meanOfElements = ( pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] ) / blockSize
  45.  *
  46.  * </pre>
  47.  *
  48.  * There are separate functions for floating point, Q31, and Q15 data types.
  49.  */
  50.  
  51. /**
  52.  * @addtogroup variance
  53.  * @{
  54.  */
  55.  
  56.  
  57. /**
  58.  * @brief Variance of the elements of a floating-point vector.
  59.  * @param[in]       *pSrc points to the input vector
  60.  * @param[in]       blockSize length of the input vector
  61.  * @param[out]      *pResult variance value returned here
  62.  * @return none.
  63.  */
  64.  
  65. void arm_var_f32(
  66.                  float32_t * pSrc,
  67.                  uint32_t blockSize,
  68.                  float32_t * pResult)
  69. {
  70.     float32_t fMean, fValue;
  71.     uint32_t blkCnt;            /* loop counter */
  72.     float32_t * pInput = pSrc;
  73.     float32_t sum = 0.0f;
  74.     float32_t fSum = 0.0f;
  75.     #if defined(ARM_MATH_DSP)
  76.     float32_t in1, in2, in3, in4;
  77.     #endif
  78.  
  79.     if (blockSize <= 1U)
  80.     {
  81.         *pResult = 0;
  82.         return;
  83.     }
  84.  
  85.     #if defined(ARM_MATH_DSP)
  86.         /* Run the below code for Cortex-M4 and Cortex-M7 */
  87.  
  88.         /*loop Unrolling */
  89.         blkCnt = blockSize >> 2U;
  90.  
  91.         /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  92.         ** a second loop below computes the remaining 1 to 3 samples. */
  93.         while (blkCnt > 0U)
  94.         {
  95.             /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
  96.             in1 = *pInput++;
  97.             in2 = *pInput++;
  98.             in3 = *pInput++;
  99.             in4 = *pInput++;
  100.  
  101.             sum += in1;
  102.             sum += in2;
  103.             sum += in3;
  104.             sum += in4;
  105.  
  106.             /* Decrement the loop counter */
  107.             blkCnt--;
  108.         }
  109.  
  110.         /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
  111.         ** No loop unrolling is used. */
  112.         blkCnt = blockSize % 0x4U;
  113.  
  114.     #else
  115.         /* Run the below code for Cortex-M0 or Cortex-M3 */
  116.  
  117.         /* Loop over blockSize number of values */
  118.         blkCnt = blockSize;
  119.  
  120.     #endif
  121.  
  122.     while (blkCnt > 0U)
  123.     {
  124.         /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
  125.         sum += *pInput++;
  126.  
  127.         /* Decrement the loop counter */
  128.         blkCnt--;
  129.     }
  130.  
  131.     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize  */
  132.     fMean = sum / (float32_t) blockSize;
  133.  
  134.     pInput = pSrc;
  135.  
  136.     #if defined(ARM_MATH_DSP)
  137.  
  138.         /*loop Unrolling */
  139.         blkCnt = blockSize >> 2U;
  140.  
  141.         /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  142.         ** a second loop below computes the remaining 1 to 3 samples. */
  143.         while (blkCnt > 0U)
  144.         {
  145.             fValue = *pInput++ - fMean;
  146.             fSum += fValue * fValue;
  147.             fValue = *pInput++ - fMean;
  148.             fSum += fValue * fValue;
  149.             fValue = *pInput++ - fMean;
  150.             fSum += fValue * fValue;
  151.             fValue = *pInput++ - fMean;
  152.             fSum += fValue * fValue;
  153.  
  154.             /* Decrement the loop counter */
  155.             blkCnt--;
  156.         }
  157.  
  158.         blkCnt = blockSize % 0x4U;
  159.     #else
  160.         /* Run the below code for Cortex-M0 or Cortex-M3 */
  161.  
  162.         /* Loop over blockSize number of values */
  163.         blkCnt = blockSize;
  164.     #endif
  165.  
  166.     while (blkCnt > 0U)
  167.     {
  168.         fValue = *pInput++ - fMean;
  169.         fSum += fValue * fValue;
  170.  
  171.         /* Decrement the loop counter */
  172.         blkCnt--;
  173.     }
  174.  
  175.     /* Variance */
  176.     *pResult = fSum / (float32_t)(blockSize - 1.0f);
  177. }
  178.  
  179. /**
  180.  * @} end of variance group
  181.  */
  182.