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# arm_var_q31.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_var_q31.c
    00009 *
    00010 * Description:  Variance of an array of Q31 type.
    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
    00066 void arm_var_q31(
    00067   q31_t * pSrc,
    00068   uint32_t blockSize,
    00069   q63_t * pResult)
    00070 {
    00071   q63_t sum = 0;                                 /* Accumulator */
    00072   q31_t meanOfSquares, squareOfMean;             /* Mean of square and square of mean */
    00073   q31_t mean;                                    /* Mean */
    00074   q31_t in;                                      /* Input variable */
    00075   q31_t t;                                       /* Temporary variable */
    00076   uint32_t blkCnt;                               /* loop counter */
    00077
    00078 #ifndef ARM_MATH_CM0
    00079
    00080   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00081
    00082   q31_t *pIn;                                    /* Temporary pointer */
    00083
    00084   pIn = pSrc;
    00085
    00086   /*loop Unrolling */
    00087   blkCnt = blockSize >> 2u;
    00088
    00089   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00090    ** a second loop below computes the remaining 1 to 3 samples. */
    00091   while(blkCnt > 0u)
    00092   {
    00093     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00094     /* Compute Sum of squares of the input samples
    00095      * and then store the result in a temporary variable, sum. */
    00096     in = *pSrc++;
    00097     sum += ((q63_t) (in) * (in));
    00098     in = *pSrc++;
    00099     sum += ((q63_t) (in) * (in));
    00100     in = *pSrc++;
    00101     sum += ((q63_t) (in) * (in));
    00102     in = *pSrc++;
    00103     sum += ((q63_t) (in) * (in));
    00104
    00105     /* Decrement the loop counter */
    00106     blkCnt--;
    00107   }
    00108
    00109   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00110    ** No loop unrolling is used. */
    00111   blkCnt = blockSize % 0x4u;
    00112
    00113   while(blkCnt > 0u)
    00114   {
    00115     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00116     /* Compute Sum of squares of the input samples
    00117      * and then store the result in a temporary variable, sum. */
    00118     in = *pSrc++;
    00119     sum += ((q63_t) (in) * (in));
    00120
    00121     /* Decrement the loop counter */
    00122     blkCnt--;
    00123   }
    00124
    00125   /* Compute Mean of squares of the input samples
    00126    * and then store the result in a temporary variable, meanOfSquares. */
    00127   t = (q31_t) ((1.0 / (blockSize - 1)) * 1073741824LL);
    00128   sum = (sum >> 31);
    00129   meanOfSquares = (q31_t) ((sum * t) >> 30);
    00130
    00131   /* Reset the accumulator */
    00132   sum = 0;
    00133
    00134   /*loop Unrolling */
    00135   blkCnt = blockSize >> 2u;
    00136
    00137   /* Reset the input working pointer */
    00138   pSrc = pIn;
    00139
    00140   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00141    ** a second loop below computes the remaining 1 to 3 samples. */
    00142   while(blkCnt > 0u)
    00143   {
    00144     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00145     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00146     sum += *pSrc++;
    00147     sum += *pSrc++;
    00148     sum += *pSrc++;
    00149     sum += *pSrc++;
    00150
    00151     /* Decrement the loop counter */
    00152     blkCnt--;
    00153   }
    00154
    00155   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00156    ** No loop unrolling is used. */
    00157   blkCnt = blockSize % 0x4u;
    00158
    00159   while(blkCnt > 0u)
    00160   {
    00161     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00162     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00163     sum += *pSrc++;
    00164
    00165     /* Decrement the loop counter */
    00166     blkCnt--;
    00167   }
    00168
    00169 #else
    00170
    00171   /* Run the below code for Cortex-M0 */
    00172
    00173   q63_t sumOfSquares = 0;                        /* Accumulator */
    00174   /* Loop over blockSize number of values */
    00175   blkCnt = blockSize;
    00176
    00177   while(blkCnt > 0u)
    00178   {
    00179     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00180     /* Compute Sum of squares of the input samples
    00181      * and then store the result in a temporary variable, sumOfSquares. */
    00182     in = *pSrc++;
    00183     sumOfSquares += ((q63_t) (in) * (in));
    00184
    00185     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00186     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00187     sum += in;
    00188
    00189     /* Decrement the loop counter */
    00190     blkCnt--;
    00191   }
    00192
    00193   /* Compute Mean of squares of the input samples
    00194    * and then store the result in a temporary variable, meanOfSquares. */
    00195   t = (q31_t) ((1.0 / (blockSize - 1)) * 1073741824LL);
    00196   sumOfSquares = (sumOfSquares >> 31);
    00197   meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30);
    00198
    00199 #endif /* #ifndef ARM_MATH_CM0 */
    00200
    00201   /* Compute mean of all input values */
    00202   t = (q31_t) ((1.0 / (blockSize * (blockSize - 1u))) * 2147483648LL);
    00203   mean = (q31_t) (sum);
    00204
    00205   /* Compute square of mean */
    00206   squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
    00207   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
    00208
    00209   /* Compute variance and then store the result to the destination */
    00210   *pResult = (q63_t) meanOfSquares - squareOfMean;
    00211
    00212 }
    00213

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