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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:        15. July 2011
    00005 * $Revision:    V1.0.10
    00006 *
    00007 * Project:      CMSIS DSP Library
    00008 * Title:        arm_std_f32.c
    00009 *
    00010 * Description:  Standard deviation of the elements of a floating-point vector.
    00011 *
    00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
    00013 *
    00014 * Version 1.0.10 2011/7/15
    00015 *    Big Endian support added and Merged M0 and M3/M4 Source code.
    00016 *
    00017 * Version 1.0.3 2010/11/29
    00018 *    Re-organized the CMSIS folders and updated documentation.
    00019 *
    00020 * Version 1.0.2 2010/11/11
    00021 *    Documentation updated.
    00022 *
    00023 * Version 1.0.1 2010/10/05
    00024 *    Production release and review comments incorporated.
    00025 *
    00026 * Version 1.0.0 2010/09/20
    00027 *    Production release and review comments incorporated.
    00028 * ---------------------------------------------------------------------------- */
    00029
    00030 #include "arm_math.h"
    00031
    00069 void arm_std_f32(
    00070   float32_t * pSrc,
    00071   uint32_t blockSize,
    00072   float32_t * pResult)
    00073 {
    00074   float32_t sum = 0.0f;                          /* Temporary result storage */
    00075
    00076 #ifndef ARM_MATH_CM0
    00077
    00078   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00079
    00080   float32_t meanOfSquares, mean, in, squareOfMean;
    00081   uint32_t blkCnt;                               /* loop counter */
    00082   float32_t *pIn;                                /* Temporary pointer */
    00083
    00084   pIn = pSrc;
    00085
    00086
    00087   /*loop Unrolling */
    00088   blkCnt = blockSize >> 2u;
    00089
    00090   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00091    ** a second loop below computes the remaining 1 to 3 samples. */
    00092   while(blkCnt > 0u)
    00093   {
    00094     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00095     /* Compute Sum of squares of the input samples
    00096      * and then store the result in a temporary variable, sum. */
    00097     in = *pSrc++;
    00098     sum += in * in;
    00099     in = *pSrc++;
    00100     sum += in * in;
    00101     in = *pSrc++;
    00102     sum += in * in;
    00103     in = *pSrc++;
    00104     sum += in * in;
    00105
    00106     /* Decrement the loop counter */
    00107     blkCnt--;
    00108   }
    00109
    00110   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00111    ** No loop unrolling is used. */
    00112   blkCnt = blockSize % 0x4u;
    00113
    00114   while(blkCnt > 0u)
    00115   {
    00116     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00117     /* Compute Sum of squares of the input samples
    00118      * and then store the result in a temporary variable, sum. */
    00119     in = *pSrc++;
    00120     sum += in * in;
    00121
    00122     /* Decrement the loop counter */
    00123     blkCnt--;
    00124   }
    00125
    00126   /* Compute Mean of squares of the input samples
    00127    * and then store the result in a temporary variable, meanOfSquares. */
    00128   meanOfSquares = sum / ((float32_t) blockSize - 1.0f);
    00129
    00130   /* Reset the accumulator */
    00131   sum = 0.0f;
    00132
    00133   /*loop Unrolling */
    00134   blkCnt = blockSize >> 2u;
    00135
    00136   /* Reset the input working pointer */
    00137   pSrc = pIn;
    00138
    00139   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00140    ** a second loop below computes the remaining 1 to 3 samples. */
    00141   while(blkCnt > 0u)
    00142   {
    00143     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00144     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00145     sum += *pSrc++;
    00146     sum += *pSrc++;
    00147     sum += *pSrc++;
    00148     sum += *pSrc++;
    00149
    00150     /* Decrement the loop counter */
    00151     blkCnt--;
    00152   }
    00153
    00154   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00155    ** No loop unrolling is used. */
    00156   blkCnt = blockSize % 0x4u;
    00157
    00158   while(blkCnt > 0u)
    00159   {
    00160     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00161     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00162     sum += *pSrc++;
    00163
    00164     /* Decrement the loop counter */
    00165     blkCnt--;
    00166   }
    00167   /* Compute mean of all input values */
    00168   mean = sum / (float32_t) blockSize;
    00169
    00170   /* Compute square of mean */
    00171   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
    00172                                   ((float32_t) blockSize - 1.0f));
    00173
    00174   /* Compute standard deviation and then store the result to the destination */
    00175   arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
    00176
    00177 #else
    00178
    00179   /* Run the below code for Cortex-M0 */
    00180
    00181   float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
    00182   float32_t squareOfSum;                         /* Square of Sum */
    00183   float32_t in;                                  /* input value */
    00184   float32_t var;                                 /* Temporary varaince storage */
    00185   uint32_t blkCnt;                               /* loop counter */
    00186
    00187   /* Loop over blockSize number of values */
    00188   blkCnt = blockSize;
    00189
    00190   while(blkCnt > 0u)
    00191   {
    00192     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00193     /* Compute Sum of squares of the input samples
    00194      * and then store the result in a temporary variable, sumOfSquares. */
    00195     in = *pSrc++;
    00196     sumOfSquares += in * in;
    00197
    00198     /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
    00199     /* Compute Sum of the input samples
    00200      * and then store the result in a temporary variable, sum. */
    00201     sum += in;
    00202
    00203     /* Decrement the loop counter */
    00204     blkCnt--;
    00205   }
    00206
    00207   /* Compute the square of sum */
    00208   squareOfSum = ((sum * sum) / (float32_t) blockSize);
    00209
    00210   /* Compute the variance */
    00211   var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
    00212
    00213   /* Compute standard deviation and then store the result to the destination */
    00214   arm_sqrt_f32(var, pResult);
    00215
    00216 #endif /* #ifndef ARM_MATH_CM0 */
    00217
    00218 }
    00219

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