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1 /* ----------------------------------------------------------------------
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2 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
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3 *
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4 * $Date: 19. March 2015
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5 * $Revision: V.1.4.5
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6 *
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7 * Project: CMSIS DSP Library
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8 * Title: arm_var_f32.c
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9 *
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10 * Description: Variance of the elements of a floating-point vector.
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11 *
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12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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13 *
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14 * Redistribution and use in source and binary forms, with or without
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15 * modification, are permitted provided that the following conditions
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16 * are met:
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17 * - Redistributions of source code must retain the above copyright
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18 * notice, this list of conditions and the following disclaimer.
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19 * - Redistributions in binary form must reproduce the above copyright
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20 * notice, this list of conditions and the following disclaimer in
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21 * the documentation and/or other materials provided with the
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22 * distribution.
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23 * - Neither the name of ARM LIMITED nor the names of its contributors
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24 * may be used to endorse or promote products derived from this
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25 * software without specific prior written permission.
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26 *
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27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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37 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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38 * POSSIBILITY OF SUCH DAMAGE.
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39 * ---------------------------------------------------------------------------- */
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40
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41 #include "arm_math.h"
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42
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43 /**
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44 * @ingroup groupStats
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45 */
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46
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47 /**
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48 * @defgroup variance Variance
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49 *
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50 * Calculates the variance of the elements in the input vector.
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51 * The underlying algorithm is used:
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52 *
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53 * <pre>
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54 * Result = (sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1)
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55 *
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56 * where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
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57 *
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58 * sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
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59 * </pre>
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60 *
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61 * There are separate functions for floating point, Q31, and Q15 data types.
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62 */
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63
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64 /**
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65 * @addtogroup variance
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66 * @{
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67 */
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68
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69
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70 /**
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71 * @brief Variance of the elements of a floating-point vector.
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72 * @param[in] *pSrc points to the input vector
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73 * @param[in] blockSize length of the input vector
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74 * @param[out] *pResult variance value returned here
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75 * @return none.
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76 *
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77 */
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78
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79
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80 void arm_var_f32(
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81 float32_t * pSrc,
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82 uint32_t blockSize,
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83 float32_t * pResult)
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84 {
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85
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86 float32_t sum = 0.0f; /* Temporary result storage */
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87 float32_t sumOfSquares = 0.0f; /* Sum of squares */
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88 float32_t in; /* input value */
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89 uint32_t blkCnt; /* loop counter */
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90
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91 #ifndef ARM_MATH_CM0_FAMILY
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92
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93 /* Run the below code for Cortex-M4 and Cortex-M3 */
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94
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95 float32_t meanOfSquares, mean, squareOfMean; /* Temporary variables */
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96
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97 if(blockSize == 1)
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98 {
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99 *pResult = 0;
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100 return;
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101 }
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102
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103 /*loop Unrolling */
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104 blkCnt = blockSize >> 2u;
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105
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106 /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
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107 ** a second loop below computes the remaining 1 to 3 samples. */
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108 while(blkCnt > 0u)
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109 {
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110 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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111 /* Compute Sum of squares of the input samples
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112 * and then store the result in a temporary variable, sum. */
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113 in = *pSrc++;
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114 sum += in;
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115 sumOfSquares += in * in;
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116 in = *pSrc++;
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117 sum += in;
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118 sumOfSquares += in * in;
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119 in = *pSrc++;
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120 sum += in;
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121 sumOfSquares += in * in;
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122 in = *pSrc++;
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123 sum += in;
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124 sumOfSquares += in * in;
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125
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126 /* Decrement the loop counter */
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127 blkCnt--;
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128 }
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129
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130 /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
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131 ** No loop unrolling is used. */
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132 blkCnt = blockSize % 0x4u;
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133
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134 while(blkCnt > 0u)
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135 {
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136 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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137 /* Compute Sum of squares of the input samples
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138 * and then store the result in a temporary variable, sum. */
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139 in = *pSrc++;
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140 sum += in;
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141 sumOfSquares += in * in;
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142
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143 /* Decrement the loop counter */
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144 blkCnt--;
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145 }
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146
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147 /* Compute Mean of squares of the input samples
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148 * and then store the result in a temporary variable, meanOfSquares. */
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149 meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
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150
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151 /* Compute mean of all input values */
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152 mean = sum / (float32_t) blockSize;
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153
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154 /* Compute square of mean */
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155 squareOfMean = (mean * mean) * (((float32_t) blockSize) /
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156 ((float32_t) blockSize - 1.0f));
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157
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158 /* Compute variance and then store the result to the destination */
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159 *pResult = meanOfSquares - squareOfMean;
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160
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161 #else
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162
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163 /* Run the below code for Cortex-M0 */
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164 float32_t squareOfSum; /* Square of Sum */
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165
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166 if(blockSize == 1)
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167 {
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168 *pResult = 0;
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169 return;
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170 }
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171
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172 /* Loop over blockSize number of values */
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173 blkCnt = blockSize;
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174
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175 while(blkCnt > 0u)
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176 {
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177 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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178 /* Compute Sum of squares of the input samples
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179 * and then store the result in a temporary variable, sumOfSquares. */
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180 in = *pSrc++;
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181 sumOfSquares += in * in;
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182
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183 /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
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184 /* Compute Sum of the input samples
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185 * and then store the result in a temporary variable, sum. */
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186 sum += in;
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187
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188 /* Decrement the loop counter */
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189 blkCnt--;
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190 }
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191
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192 /* Compute the square of sum */
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193 squareOfSum = ((sum * sum) / (float32_t) blockSize);
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194
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195 /* Compute the variance */
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196 *pResult = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
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197
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198 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
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199
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200 }
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201
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202 /**
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203 * @} end of variance group
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204 */
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