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# arm_var_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_var_q15.c
    00009 *
    00010 * Description:  Variance 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
    00061 void arm_var_q15(
    00062   q15_t * pSrc,
    00063   uint32_t blockSize,
    00064   q31_t * pResult)
    00065 {
    00066   q63_t sum = 0;                                 /* Accumulator */
    00067   q31_t meanOfSquares, squareOfMean;             /* Mean of square and square of mean */
    00068   q15_t mean;                                    /* mean */
    00069   q31_t in;                                      /* Input variable */
    00070   q15_t in1;                                     /* Temporary variable */
    00071   uint32_t blkCnt;                               /* loop counter */
    00072   q15_t t;                                       /* Temporary variable */
    00073   q15_t *pIn;                                    /* Temporary pointer */
    00074
    00075   pIn = pSrc;
    00076
    00077   /*loop Unrolling */
    00078   blkCnt = blockSize >> 2u;
    00079
    00080   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00081    ** a second loop below computes the remaining 1 to 3 samples. */
    00082   while(blkCnt > 0u)
    00083   {
    00084     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00085     /* Compute Sum of squares of the input samples
    00086      * and then store the result in a temporary variable, sum. */
    00087     in = *__SIMD32(pSrc)++;
    00088     sum = __SMLALD(in, in, sum);
    00089     in = *__SIMD32(pSrc)++;
    00090     sum = __SMLALD(in, in, sum);
    00091
    00092     /* Decrement the loop counter */
    00093     blkCnt--;
    00094   }
    00095
    00096   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00097    ** No loop unrolling is used. */
    00098   blkCnt = blockSize % 0x4u;
    00099
    00100   while(blkCnt > 0u)
    00101   {
    00102     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00103     /* Compute Sum of squares of the input samples
    00104      * and then store the result in a temporary variable, sum. */
    00105     in1 = *pSrc++;
    00106     sum = __SMLALD(in1, in1, sum);
    00107
    00108     /* Decrement the loop counter */
    00109     blkCnt--;
    00110   }
    00111
    00112   /* Compute Mean of squares of the input samples
    00113    * and then store the result in a temporary variable, meanOfSquares. */
    00114   t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
    00115   sum = __SSAT((sum >> 15u), 16u);
    00116
    00117   meanOfSquares = (q31_t) ((sum * t) >> 14u);
    00118
    00119   /* Reset the accumulator */
    00120   sum = 0;
    00121
    00122   /*loop Unrolling */
    00123   blkCnt = blockSize >> 2u;
    00124
    00125   /* Reset the input working pointer */
    00126   pSrc = pIn;
    00127
    00128   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00129    ** a second loop below computes the remaining 1 to 3 samples. */
    00130   while(blkCnt > 0u)
    00131   {
    00132     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00133     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00134     sum += *pSrc++;
    00135     sum += *pSrc++;
    00136     sum += *pSrc++;
    00137     sum += *pSrc++;
    00138
    00139     /* Decrement the loop counter */
    00140     blkCnt--;
    00141   }
    00142
    00143   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00144    ** No loop unrolling is used. */
    00145   blkCnt = blockSize % 0x4u;
    00146
    00147   while(blkCnt > 0u)
    00148   {
    00149     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00150     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00151     sum += *pSrc++;
    00152
    00153     /* Decrement the loop counter */
    00154     blkCnt--;
    00155   }
    00156
    00157   /* Compute mean of all input values */
    00158   t = (q15_t) ((1.0f / (float32_t) (blockSize * (blockSize - 1u))) * 32768);
    00159   mean = __SSAT(sum, 16u);
    00160
    00161   /* Compute square of mean */
    00162   squareOfMean = ((q31_t) mean * mean) >> 15;
    00163   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
    00164
    00165   /* Compute variance and then store the result to the destination */
    00166   *pResult = (meanOfSquares - squareOfMean);
    00167
    00168 }
    00169

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