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Drivers/CMSIS/DSP/Source/StatisticsFunctions/arm_std_f32.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_std_f32.c
+ * Description:  Standard deviation of the elements of a floating-point vector
+ *
+ * $Date:        23 April 2021
+ * $Revision:    V1.9.0
+ *
+ * Target Processor: Cortex-M and Cortex-A cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "dsp/statistics_functions.h"
+
+/**
+  @ingroup groupStats
+ */
+
+/**
+  @defgroup STD Standard deviation
+
+  Calculates the standard deviation of the elements in the input vector.
+
+  The float implementation is relying on arm_var_f32 which is using a two-pass algorithm
+  to avoid problem of numerical instabilities and cancellation errors.
+
+  Fixed point versions are using the standard textbook algorithm since the fixed point
+  numerical behavior is different from the float one.
+
+  Algorithm for fixed point versions is summarized below:
+
+
+  <pre>
+      Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1))
+
+      sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
+      sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
+  </pre>
+
+  There are separate functions for floating point, Q31, and Q15 data types.
+ */
+
+/**
+  @addtogroup STD
+  @{
+ */
+
+/**
+  @brief         Standard deviation of the elements of a floating-point vector.
+  @param[in]     pSrc       points to the input vector
+  @param[in]     blockSize  number of samples in input vector
+  @param[out]    pResult    standard deviation value returned here
+  @return        none
+ */
+void arm_std_f32(
+  const float32_t * pSrc,
+        uint32_t blockSize,
+        float32_t * pResult)
+{
+  float32_t var;
+  arm_var_f32(pSrc,blockSize,&var);
+  arm_sqrt_f32(var, pResult);
+}
+
+/**
+  @} end of STD group
+ */