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# arm_std_f32.c

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    00001 /* ----------------------------------------------------------------------
    00002 * Copyright (C) 2010 ARM Limited. All rights reserved.
    00003 *
    00004 * $Date:        29. November 2010
    00005 * $Revision:    V1.0.3
    00006 *
    00007 * Project:      CMSIS DSP Library
    00008 * Title:        arm_std_f32.c
    00009 *
    00010 * Description:  Standard deviation of an array of F32 type.
    00011 *
    00012 * Target Processor: Cortex-M4/Cortex-M3
    00013 *
    00014 * Version 1.0.3 2010/11/29
    00015 *    Re-organized the CMSIS folders and updated documentation.
    00016 *
    00017 * Version 1.0.2 2010/11/11
    00018 *    Documentation updated.
    00019 *
    00020 * Version 1.0.1 2010/10/05
    00021 *    Production release and review comments incorporated.
    00022 *
    00023 * Version 1.0.0 2010/09/20
    00024 *    Production release and review comments incorporated.
    00025 * ---------------------------------------------------------------------------- */
    00026
    00027 #include "arm_math.h"
    00028
    00066 void arm_std_f32(
    00067   float32_t * pSrc,
    00068   uint32_t blockSize,
    00069   float32_t * pResult)
    00070 {
    00071   float32_t sum = 0.0f;                            /* Temporary result storage */
    00072   float32_t meanOfSquares, mean, in, squareOfMean;
    00073   uint32_t blkCnt;                                 /* loop counter */
    00074   float32_t *pIn;                                  /* Temporary pointer */
    00075
    00076   pIn = pSrc;
    00077
    00078
    00079   /*loop Unrolling */
    00080   blkCnt = blockSize >> 2u;
    00081
    00082   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00083    ** a second loop below computes the remaining 1 to 3 samples. */
    00084   while(blkCnt > 0u)
    00085   {
    00086     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00087     /* Compute Sum of squares of the input samples
    00088      * and then store the result in a temporary variable, sum. */
    00089     in = *pSrc++;
    00090     sum += in * in;
    00091     in = *pSrc++;
    00092     sum += in * in;
    00093     in = *pSrc++;
    00094     sum += in * in;
    00095     in = *pSrc++;
    00096     sum += in * in;
    00097
    00098     /* Decrement the loop counter */
    00099     blkCnt--;
    00100   }
    00101
    00102   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00103    ** No loop unrolling is used. */
    00104   blkCnt = blockSize % 0x4u;
    00105
    00106   while(blkCnt > 0u)
    00107   {
    00108     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00109     /* Compute Sum of squares of the input samples
    00110      * and then store the result in a temporary variable, sum. */
    00111     in = *pSrc++;
    00112     sum += in * in;
    00113
    00114     /* Decrement the loop counter */
    00115     blkCnt--;
    00116   }
    00117
    00118   /* Compute Mean of squares of the input samples
    00119    * and then store the result in a temporary variable, meanOfSquares. */
    00120   meanOfSquares = sum / ((float32_t) blockSize - 1.0f);
    00121
    00122   /* Reset the accumulator */
    00123   sum = 0.0f;
    00124
    00125   /*loop Unrolling */
    00126   blkCnt = blockSize >> 2u;
    00127
    00128   /* Reset the input working pointer */
    00129   pSrc = pIn;
    00130
    00131   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00132    ** a second loop below computes the remaining 1 to 3 samples. */
    00133   while(blkCnt > 0u)
    00134   {
    00135     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00136     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00137     sum += *pSrc++;
    00138     sum += *pSrc++;
    00139     sum += *pSrc++;
    00140     sum += *pSrc++;
    00141
    00142     /* Decrement the loop counter */
    00143     blkCnt--;
    00144   }
    00145
    00146   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00147    ** No loop unrolling is used. */
    00148   blkCnt = blockSize % 0x4u;
    00149
    00150   while(blkCnt > 0u)
    00151   {
    00152     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00153     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00154     sum += *pSrc++;
    00155
    00156     /* Decrement the loop counter */
    00157     blkCnt--;
    00158   }
    00159   /* Compute mean of all input values */
    00160   mean = sum / (float32_t) blockSize;
    00161
    00162   /* Compute square of mean */
    00163   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
    00164                                   ((float32_t) blockSize - 1.0f));
    00165
    00166   /* Compute standard deviation and then store the result to the destination */
    00167   arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
    00168
    00169 }
    00170

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