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