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git.gir.st - tmk_keyboard.git/blob - tmk_core/tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/StatisticsFunctions/arm_std_f32.c
1 /* ----------------------------------------------------------------------
2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
4 * $Date: 17. January 2013
7 * Project: CMSIS DSP Library
10 * Description: Standard deviation of the elements of a floating-point vector.
12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
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
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.
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
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38 * POSSIBILITY OF SUCH DAMAGE.
39 * ---------------------------------------------------------------------------- */
48 * @defgroup STD Standard deviation
50 * Calculates the standard deviation of the elements in the input vector.
51 * The underlying algorithm is used:
54 * Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1))
56 * where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
58 * sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
61 * There are separate functions for floating point, Q31, and Q15 data types.
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
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 */
90 #ifndef ARM_MATH_CM0_FAMILY
92 /* Run the below code for Cortex-M4 and Cortex-M3 */
94 float32_t meanOfSquares
, mean
, squareOfMean
;
97 blkCnt
= blockSize
>> 2u;
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. */
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. */
108 sumOfSquares
+= in
* in
;
111 sumOfSquares
+= in
* in
;
114 sumOfSquares
+= in
* in
;
117 sumOfSquares
+= in
* in
;
119 /* Decrement the loop counter */
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
;
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. */
134 sumOfSquares
+= in
* in
;
136 /* Decrement the loop counter */
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
);
144 /* Compute mean of all input values */
145 mean
= sum
/ (float32_t
) blockSize
;
147 /* Compute square of mean */
148 squareOfMean
= (mean
* mean
) * (((float32_t
) blockSize
) /
149 ((float32_t
) blockSize
- 1.0f
));
151 /* Compute standard deviation and then store the result to the destination */
152 arm_sqrt_f32((meanOfSquares
- squareOfMean
), pResult
);
156 /* Run the below code for Cortex-M0 */
158 float32_t squareOfSum
; /* Square of Sum */
159 float32_t var
; /* Temporary varaince storage */
161 /* Loop over blockSize number of values */
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. */
170 sumOfSquares
+= in
* in
;
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. */
177 /* Decrement the loop counter */
181 /* Compute the square of sum */
182 squareOfSum
= ((sum
* sum
) / (float32_t
) blockSize
);
184 /* Compute the variance */
185 var
= ((sumOfSquares
- squareOfSum
) / (float32_t
) (blockSize
- 1.0f
));
187 /* Compute standard deviation and then store the result to the destination */
188 arm_sqrt_f32(var
, pResult
);
190 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
195 * @} end of STD group