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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:        15. July 2011
    00005 * $Revision:    V1.0.10
    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/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_std_q31(
    00067   q31_t * pSrc,
    00068   uint32_t blockSize,
    00069   q31_t * pResult)
    00070 {
    00071   q63_t sum = 0;                                 /* Accumulator */
    00072   q31_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
    00073   q31_t mean;                                    /* mean */
    00074   q31_t in;                                      /* input value */
    00075   q31_t t;                                       /* Temporary variable */
    00076   uint32_t blkCnt;                               /* loop counter */
    00077
    00078
    00079 #ifndef ARM_MATH_CM0
    00080
    00081   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00082
    00083   q31_t *pIn;                                    /* Temporary pointer */
    00084
    00085   pIn = pSrc;
    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 += ((q63_t) (in) * (in));
    00099     in = *pSrc++;
    00100     sum += ((q63_t) (in) * (in));
    00101     in = *pSrc++;
    00102     sum += ((q63_t) (in) * (in));
    00103     in = *pSrc++;
    00104     sum += ((q63_t) (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 += ((q63_t) (in) * (in));
    00121
    00122     /* Decrement the loop counter */
    00123     blkCnt--;
    00124   }
    00125
    00126   t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
    00127
    00128   /* Compute Mean of squares of the input samples
    00129    * and then store the result in a temporary variable, meanOfSquares. */
    00130   sum = (sum >> 31);
    00131   meanOfSquares = (q31_t) ((sum * t) >> 30);
    00132
    00133   /* Reset the accumulator */
    00134   sum = 0;
    00135
    00136   /*loop Unrolling */
    00137   blkCnt = blockSize >> 2u;
    00138
    00139   /* Reset the input working pointer */
    00140   pSrc = pIn;
    00141
    00142   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00143    ** a second loop below computes the remaining 1 to 3 samples. */
    00144   while(blkCnt > 0u)
    00145   {
    00146     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00147     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00148     sum += *pSrc++;
    00149     sum += *pSrc++;
    00150     sum += *pSrc++;
    00151     sum += *pSrc++;
    00152
    00153     /* Decrement the loop counter */
    00154     blkCnt--;
    00155   }
    00156
    00157   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00158    ** No loop unrolling is used. */
    00159   blkCnt = blockSize % 0x4u;
    00160
    00161   while(blkCnt > 0u)
    00162   {
    00163     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00164     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00165     sum += *pSrc++;
    00166
    00167     /* Decrement the loop counter */
    00168     blkCnt--;
    00169   }
    00170
    00171 #else
    00172
    00173   /* Run the below code for Cortex-M0 */
    00174
    00175   q63_t sumOfSquares = 0;                        /* Accumulator */
    00176   /* Loop over blockSize number of values */
    00177   blkCnt = blockSize;
    00178
    00179   while(blkCnt > 0u)
    00180   {
    00181     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00182     /* Compute Sum of squares of the input samples
    00183      * and then store the result in a temporary variable, sumOfSquares. */
    00184     in = *pSrc++;
    00185     sumOfSquares += ((q63_t) (in) * (in));
    00186
    00187     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00188     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00189     sum += in;
    00190
    00191     /* Decrement the loop counter */
    00192     blkCnt--;
    00193   }
    00194
    00195   /* Compute Mean of squares of the input samples
    00196    * and then store the result in a temporary variable, meanOfSquares. */
    00197   t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
    00198   sumOfSquares = (sumOfSquares >> 31);
    00199   meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30);
    00200
    00201 #endif /* #ifndef ARM_MATH_CM0 */
    00202
    00203   /* Compute mean of all input values */
    00204   t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f);
    00205   mean = (q31_t) (sum);
    00206
    00207   /* Compute square of mean */
    00208   squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
    00209   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
    00210
    00211
    00212   /* Compute standard deviation and then store the result to the destination */
    00213   arm_sqrt_q31(meanOfSquares - squareOfMean, pResult);
    00214
    00215 }
    00216

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