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# arm_std_q15.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_q15.c
    00009 *
    00010 * Description:  Standard deviation of an array of Q15 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
    00059 void arm_std_q15(
    00060   q15_t * pSrc,
    00061   uint32_t blockSize,
    00062   q15_t * pResult)
    00063 {
    00064   q63_t sum = 0;                                 /* Accumulator */
    00065   q31_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
    00066   q15_t mean;                                    /* mean */
    00067   q31_t in;                                      /* input value */
    00068   q15_t in1;                                     /* input value */
    00069   uint32_t blkCnt;                               /* loop counter */
    00070   q15_t t;                                       /* Temporary variable */
    00071   q15_t *pIn;                                    /* Temporary pointer */
    00072
    00073   pIn = pSrc;
    00074
    00075   /*loop Unrolling */
    00076   blkCnt = blockSize >> 2u;
    00077
    00078   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00079    ** a second loop below computes the remaining 1 to 3 samples. */
    00080   while(blkCnt > 0u)
    00081   {
    00082     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00083     /* Compute Sum of squares of the input samples
    00084      * and then store the result in a temporary variable, sum. */
    00085     in = *__SIMD32(pSrc)++;
    00086     sum = __SMLALD(in, in, sum);
    00087     in = *__SIMD32(pSrc)++;
    00088     sum = __SMLALD(in, in, sum);
    00089
    00090     /* Decrement the loop counter */
    00091     blkCnt--;
    00092   }
    00093
    00094   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00095    ** No loop unrolling is used. */
    00096   blkCnt = blockSize % 0x4u;
    00097
    00098   while(blkCnt > 0u)
    00099   {
    00100     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00101     /* Compute Sum of squares of the input samples
    00102      * and then store the result in a temporary variable, sum. */
    00103     in1 = *pSrc++;
    00104     sum = __SMLALD(in1, in1, sum);
    00105
    00106     /* Decrement the loop counter */
    00107     blkCnt--;
    00108   }
    00109
    00110   /* Compute Mean of squares of the input samples
    00111    * and then store the result in a temporary variable, meanOfSquares. */
    00112   t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL);
    00113   sum = __SSAT((sum >> 15u), 16u);
    00114
    00115   meanOfSquares = (q31_t) ((sum * t) >> 14u);
    00116
    00117   /* Reset the accumulator */
    00118   sum = 0;
    00119
    00120   /*loop Unrolling */
    00121   blkCnt = blockSize >> 2u;
    00122
    00123   /* Reset the input working pointer */
    00124   pSrc = pIn;
    00125
    00126   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00127    ** a second loop below computes the remaining 1 to 3 samples. */
    00128   while(blkCnt > 0u)
    00129   {
    00130     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00131     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00132     sum += *pSrc++;
    00133     sum += *pSrc++;
    00134     sum += *pSrc++;
    00135     sum += *pSrc++;
    00136
    00137     /* Decrement the loop counter */
    00138     blkCnt--;
    00139   }
    00140
    00141   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00142    ** No loop unrolling is used. */
    00143   blkCnt = blockSize % 0x4u;
    00144
    00145   while(blkCnt > 0u)
    00146   {
    00147     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00148     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00149     sum += *pSrc++;
    00150
    00151     /* Decrement the loop counter */
    00152     blkCnt--;
    00153   }
    00154   /* Compute mean of all input values */
    00155   t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL);
    00156   mean = (q15_t) __SSAT(sum, 16u);
    00157
    00158   /* Compute square of mean */
    00159   squareOfMean = ((q31_t) mean * mean) >> 15;
    00160   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
    00161
    00162   /* mean of the squares minus the square of the mean. */
    00163   in1 = (q15_t) (meanOfSquares - squareOfMean);
    00164
    00165   /* Compute standard deviation and store the result to the destination */
    00166   arm_sqrt_q15(in1, pResult);
    00167 }
    00168

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