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yaokon/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:        27. January 2017
+ * $Revision:    V.1.5.1
+ *
+ * Target Processor: Cortex-M cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2017 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 "arm_math.h"
+
+/**
+ * @ingroup groupStats
+ */
+
+/**
+ * @defgroup STD Standard deviation
+ *
+ * Calculates the standard deviation of the elements in the input vector.
+ * The underlying algorithm is used:
+ *
+ * <pre>
+ *   Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1))
+ *
+ *     where, 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 length of the input vector
+ * @param[out]      *pResult standard deviation value returned here
+ * @return none.
+ */
+
+void arm_std_f32(
+  float32_t * pSrc,
+  uint32_t blockSize,
+  float32_t * pResult)
+{
+  float32_t sum = 0.0f;                          /* Temporary result storage */
+  float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
+  float32_t in;                                  /* input value */
+  uint32_t blkCnt;                               /* loop counter */
+#if defined (ARM_MATH_DSP)
+  float32_t meanOfSquares, mean, squareOfMean;   /* Temporary variables */
+#else
+  float32_t squareOfSum;                         /* Square of Sum */
+  float32_t var;                                 /* Temporary varaince storage */
+#endif
+
+  if (blockSize == 1U)
+  {
+    *pResult = 0;
+    return;
+  }
+
+#if defined (ARM_MATH_DSP)
+  /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+  /*loop Unrolling */
+  blkCnt = blockSize >> 2U;
+
+  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
+   ** a second loop below computes the remaining 1 to 3 samples. */
+  while (blkCnt > 0U)
+  {
+    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
+    /* Compute Sum of squares of the input samples
+     * and then store the result in a temporary variable, sum. */
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += in * in;
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += in * in;
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += in * in;
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += in * in;
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
+   ** No loop unrolling is used. */
+  blkCnt = blockSize % 0x4U;
+
+  while (blkCnt > 0U)
+  {
+    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
+    /* Compute Sum of squares of the input samples
+     * and then store the result in a temporary variable, sum. */
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += in * in;
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  /* Compute Mean of squares of the input samples
+   * and then store the result in a temporary variable, meanOfSquares. */
+  meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
+
+  /* Compute mean of all input values */
+  mean = sum / (float32_t) blockSize;
+
+  /* Compute square of mean */
+  squareOfMean = (mean * mean) * (((float32_t) blockSize) /
+                                  ((float32_t) blockSize - 1.0f));
+
+  /* Compute standard deviation and then store the result to the destination */
+  arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
+
+#else
+  /* Run the below code for Cortex-M0 */
+
+  /* Loop over blockSize number of values */
+  blkCnt = blockSize;
+
+  while (blkCnt > 0U)
+  {
+    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
+    /* Compute Sum of squares of the input samples
+     * and then store the result in a temporary variable, sumOfSquares. */
+    in = *pSrc++;
+    sumOfSquares += in * in;
+
+    /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
+    /* Compute Sum of the input samples
+     * and then store the result in a temporary variable, sum. */
+    sum += in;
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  /* Compute the square of sum */
+  squareOfSum = ((sum * sum) / (float32_t) blockSize);
+
+  /* Compute the variance */
+  var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
+
+  /* Compute standard deviation and then store the result to the destination */
+  arm_sqrt_f32(var, pResult);
+
+#endif /* #if defined (ARM_MATH_DSP) */
+}
+
+/**
+ * @} end of STD group
+ */