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# arm_std_q31.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_q31.c
    00009 *
    00010 * Description:  Standard deviation of an array of Q31 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
    00063 void arm_std_q31(
    00064   q31_t * pSrc,
    00065   uint32_t blockSize,
    00066   q31_t * pResult)
    00067 {
    00068   q63_t sum = 0;                                 /* Accumulator */
    00069   q31_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
    00070   q31_t mean;                                    /* mean */
    00071   q31_t in;                                      /* input value */
    00072   q31_t t;                                       /* Temporary variable */
    00073   uint32_t blkCnt;                               /* loop counter */
    00074   q31_t *pIn;                                    /* Temporary pointer */
    00075
    00076   pIn = pSrc;
    00077
    00078   /*loop Unrolling */
    00079   blkCnt = blockSize >> 2u;
    00080
    00081   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00082    ** a second loop below computes the remaining 1 to 3 samples. */
    00083   while(blkCnt > 0u)
    00084   {
    00085     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00086     /* Compute Sum of squares of the input samples
    00087      * and then store the result in a temporary variable, sum. */
    00088     in = *pSrc++;
    00089     sum += ((q63_t) (in) * (in));
    00090     in = *pSrc++;
    00091     sum += ((q63_t) (in) * (in));
    00092     in = *pSrc++;
    00093     sum += ((q63_t) (in) * (in));
    00094     in = *pSrc++;
    00095     sum += ((q63_t) (in) * (in));
    00096
    00097     /* Decrement the loop counter */
    00098     blkCnt--;
    00099   }
    00100
    00101   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00102    ** No loop unrolling is used. */
    00103   blkCnt = blockSize % 0x4u;
    00104
    00105   while(blkCnt > 0u)
    00106   {
    00107     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00108     /* Compute Sum of squares of the input samples
    00109      * and then store the result in a temporary variable, sum. */
    00110     in = *pSrc++;
    00111     sum += ((q63_t) (in) * (in));
    00112
    00113     /* Decrement the loop counter */
    00114     blkCnt--;
    00115   }
    00116
    00117   t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
    00118
    00119   /* Compute Mean of squares of the input samples
    00120    * and then store the result in a temporary variable, meanOfSquares. */
    00121   sum = (sum >> 31);
    00122   meanOfSquares = (q31_t) ((sum * t) >> 30);
    00123
    00124   /* Reset the accumulator */
    00125   sum = 0;
    00126
    00127   /*loop Unrolling */
    00128   blkCnt = blockSize >> 2u;
    00129
    00130   /* Reset the input working pointer */
    00131   pSrc = pIn;
    00132
    00133   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00134    ** a second loop below computes the remaining 1 to 3 samples. */
    00135   while(blkCnt > 0u)
    00136   {
    00137     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00138     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00139     sum += *pSrc++;
    00140     sum += *pSrc++;
    00141     sum += *pSrc++;
    00142     sum += *pSrc++;
    00143
    00144     /* Decrement the loop counter */
    00145     blkCnt--;
    00146   }
    00147
    00148   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00149    ** No loop unrolling is used. */
    00150   blkCnt = blockSize % 0x4u;
    00151
    00152   while(blkCnt > 0u)
    00153   {
    00154     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00155     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00156     sum += *pSrc++;
    00157
    00158     /* Decrement the loop counter */
    00159     blkCnt--;
    00160   }
    00161   /* Compute mean of all input values */
    00162   t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f);
    00163   mean = (q31_t) (sum);
    00164
    00165   /* Compute square of mean */
    00166   squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
    00167   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
    00168
    00169   /* Compute standard deviation and then store the result to the destination */
    00170   arm_sqrt_q31(meanOfSquares - squareOfMean, pResult);
    00171
    00172 }
    00173

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