/* ---------------------------------------------------------------------- * Copyright (C) 2010 ARM Limited. All rights reserved. * * $Date: 29. November 2010 * $Revision: V1.0.3 * * Project: CMSIS DSP Library * Title: arm_std_f32.c * * Description: Standard deviation of an array of F32 type. * * Target Processor: Cortex-M4/Cortex-M3 * * 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: * *
  
 * 	Result = sqrt((sumOfSquares - sum2 / 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] 
 * 
* * 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 meanOfSquares, mean, in, squareOfMean; uint32_t blkCnt; /* loop counter */ float32_t *pIn; /* Temporary pointer */ pIn = pSrc; /*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 * in; in = *pSrc++; sum += in * in; in = *pSrc++; sum += in * in; in = *pSrc++; sum += 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 * 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 = sum / ((float32_t) blockSize - 1.0f); /* Reset the accumulator */ sum = 0.0f; /*loop Unrolling */ blkCnt = blockSize >> 2u; /* Reset the input working pointer */ pSrc = pIn; /* 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[1] + A[2] + ... + A[blockSize-1]) */ /* Compute sum of all input values and then store the result in a temporary variable, sum. */ sum += *pSrc++; sum += *pSrc++; sum += *pSrc++; sum += *pSrc++; /* 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[1] + A[2] + ... + A[blockSize-1]) */ /* Compute sum of all input values and then store the result in a temporary variable, sum. */ sum += *pSrc++; /* Decrement the loop counter */ blkCnt--; } /* 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); } /** * @} end of STD group */