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git.gir.st - tmk_keyboard.git/blob - tmk_core/tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/StatisticsFunctions/arm_std_q31.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 an array of Q31 type.
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 * -------------------------------------------------------------------- */
54 * @brief Standard deviation of the elements of a Q31 vector.
55 * @param[in] *pSrc points to the input vector
56 * @param[in] blockSize length of the input vector
57 * @param[out] *pResult standard deviation value returned here
60 * <b>Scaling and Overflow Behavior:</b>
63 * The function is implemented using an internal 64-bit accumulator.
64 * The input is represented in 1.31 format, and intermediate multiplication
65 * yields a 2.62 format.
66 * The accumulator maintains full precision of the intermediate multiplication results,
67 * but provides only a single guard bit.
68 * There is no saturation on intermediate additions.
69 * If the accumulator overflows it wraps around and distorts the result.
70 * In order to avoid overflows completely the input signal must be scaled down by
71 * log2(blockSize) bits, as a total of blockSize additions are performed internally.
72 * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.
82 q63_t sum
= 0; /* Accumulator */
83 q31_t meanOfSquares
, squareOfMean
; /* square of mean and mean of square */
84 q31_t mean
; /* mean */
85 q31_t in
; /* input value */
86 q31_t t
; /* Temporary variable */
87 uint32_t blkCnt
; /* loop counter */
88 q63_t sumOfSquares
= 0; /* Accumulator */
90 #ifndef ARM_MATH_CM0_FAMILY
92 /* Run the below code for Cortex-M4 and Cortex-M3 */
95 blkCnt
= blockSize
>> 2u;
97 /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
98 ** a second loop below computes the remaining 1 to 3 samples. */
101 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
102 /* Compute Sum of squares of the input samples
103 * and then store the result in a temporary variable, sum. */
106 sumOfSquares
+= ((q63_t
) (in
) * (in
));
109 sumOfSquares
+= ((q63_t
) (in
) * (in
));
112 sumOfSquares
+= ((q63_t
) (in
) * (in
));
115 sumOfSquares
+= ((q63_t
) (in
) * (in
));
117 /* Decrement the loop counter */
121 /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
122 ** No loop unrolling is used. */
123 blkCnt
= blockSize
% 0x4u
;
127 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
128 /* Compute Sum of squares of the input samples
129 * and then store the result in a temporary variable, sum. */
132 sumOfSquares
+= ((q63_t
) (in
) * (in
));
134 /* Decrement the loop counter */
138 t
= (q31_t
) ((1.0f
/ (float32_t
) (blockSize
- 1u)) * 1073741824.0f
);
140 /* Compute Mean of squares of the input samples
141 * and then store the result in a temporary variable, meanOfSquares. */
142 sumOfSquares
= (sumOfSquares
>> 31);
143 meanOfSquares
= (q31_t
) ((sumOfSquares
* t
) >> 30);
147 /* Run the below code for Cortex-M0 */
149 /* Loop over blockSize number of values */
154 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
155 /* Compute Sum of squares of the input samples
156 * and then store the result in a temporary variable, sumOfSquares. */
158 sumOfSquares
+= ((q63_t
) (in
) * (in
));
160 /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
161 /* Compute sum of all input values and then store the result in a temporary variable, sum. */
164 /* Decrement the loop counter */
168 /* Compute Mean of squares of the input samples
169 * and then store the result in a temporary variable, meanOfSquares. */
170 t
= (q31_t
) ((1.0f
/ (float32_t
) (blockSize
- 1u)) * 1073741824.0f
);
171 sumOfSquares
= (sumOfSquares
>> 31);
172 meanOfSquares
= (q31_t
) ((sumOfSquares
* t
) >> 30);
174 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
176 /* Compute mean of all input values */
177 t
= (q31_t
) ((1.0f
/ (blockSize
* (blockSize
- 1u))) * 2147483648.0f
);
178 mean
= (q31_t
) (sum
);
180 /* Compute square of mean */
181 squareOfMean
= (q31_t
) (((q63_t
) mean
* mean
) >> 31);
182 squareOfMean
= (q31_t
) (((q63_t
) squareOfMean
* t
) >> 31);
185 /* Compute standard deviation and then store the result to the destination */
186 arm_sqrt_q31(meanOfSquares
- squareOfMean
, pResult
);
191 * @} end of STD group