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+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010 ARM Limited. All rights reserved.    
+*    
+* $Date:        15. February 2012  
+* $Revision: 	V1.1.0  
+*    
+* Project: 	    CMSIS DSP Library    
+* Title:		arm_std_f32.c    
+*    
+* Description:	Standard deviation of the elements of a floating-point vector.  
+*    
+* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
+*  
+* Version 1.1.0 2012/02/15 
+*    Updated with more optimizations, bug fixes and minor API changes.  
+*   
+* Version 1.0.10 2011/7/15  
+*    Big Endian support added and Merged M0 and M3/M4 Source code.   
+*    
+* Version 1.0.3 2010/11/29   
+*    Re-organized the CMSIS folders and updated documentation.    
+*     
+* Version 1.0.2 2010/11/11    
+*    Documentation updated.     
+*    
+* Version 1.0.1 2010/10/05     
+*    Production release and review comments incorporated.    
+*    
+* Version 1.0.0 2010/09/20     
+*    Production release and review comments incorporated.    
+* ---------------------------------------------------------------------------- */
+
+#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 */
+
+#ifndef ARM_MATH_CM0
+
+  /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+  float32_t meanOfSquares, mean, squareOfMean;
+
+  /*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 */
+
+  float32_t squareOfSum;                         /* Square of Sum */
+  float32_t var;                                 /* Temporary varaince storage */
+
+  /* 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 /* #ifndef ARM_MATH_CM0 */
+
+}
+
+/**    
+ * @} end of STD group    
+ */