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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:        15. July 2011
    00005 * $Revision:    V1.0.10
    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/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
    00062 void arm_std_q15(
    00063   q15_t * pSrc,
    00064   uint32_t blockSize,
    00065   q15_t * pResult)
    00066 {
    00067   q63_t sum = 0;                                 /* Accumulator */
    00068   q31_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
    00069   q15_t mean;                                    /* mean */
    00070   uint32_t blkCnt;                               /* loop counter */
    00071   q15_t t;                                       /* Temporary variable */
    00072
    00073 #ifndef ARM_MATH_CM0
    00074
    00075   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00076
    00077   q15_t *pIn;                                    /* Temporary pointer */
    00078   q31_t in;                                      /* input value */
    00079   q15_t in1;                                     /* input value */
    00080
    00081   pIn = pSrc;
    00082
    00083   /*loop Unrolling */
    00084   blkCnt = blockSize >> 2u;
    00085
    00086   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00087    ** a second loop below computes the remaining 1 to 3 samples. */
    00088   while(blkCnt > 0u)
    00089   {
    00090     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00091     /* Compute Sum of squares of the input samples
    00092      * and then store the result in a temporary variable, sum. */
    00093     in = *__SIMD32(pSrc)++;
    00094     sum = __SMLALD(in, in, sum);
    00095     in = *__SIMD32(pSrc)++;
    00096     sum = __SMLALD(in, in, sum);
    00097
    00098     /* Decrement the loop counter */
    00099     blkCnt--;
    00100   }
    00101
    00102   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00103    ** No loop unrolling is used. */
    00104   blkCnt = blockSize % 0x4u;
    00105
    00106   while(blkCnt > 0u)
    00107   {
    00108     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00109     /* Compute Sum of squares of the input samples
    00110      * and then store the result in a temporary variable, sum. */
    00111     in1 = *pSrc++;
    00112     sum = __SMLALD(in1, in1, sum);
    00113
    00114     /* Decrement the loop counter */
    00115     blkCnt--;
    00116   }
    00117
    00118   /* Compute Mean of squares of the input samples
    00119    * and then store the result in a temporary variable, meanOfSquares. */
    00120   t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL);
    00121   sum = __SSAT((sum >> 15u), 16u);
    00122
    00123   meanOfSquares = (q31_t) ((sum * t) >> 14u);
    00124
    00125   /* Reset the accumulator */
    00126   sum = 0;
    00127
    00128   /*loop Unrolling */
    00129   blkCnt = blockSize >> 2u;
    00130
    00131   /* Reset the input working pointer */
    00132   pSrc = pIn;
    00133
    00134   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00135    ** a second loop below computes the remaining 1 to 3 samples. */
    00136   while(blkCnt > 0u)
    00137   {
    00138     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00139     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00140     sum += *pSrc++;
    00141     sum += *pSrc++;
    00142     sum += *pSrc++;
    00143     sum += *pSrc++;
    00144
    00145     /* Decrement the loop counter */
    00146     blkCnt--;
    00147   }
    00148
    00149   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00150    ** No loop unrolling is used. */
    00151   blkCnt = blockSize % 0x4u;
    00152
    00153   while(blkCnt > 0u)
    00154   {
    00155     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00156     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00157     sum += *pSrc++;
    00158
    00159     /* Decrement the loop counter */
    00160     blkCnt--;
    00161   }
    00162   /* Compute mean of all input values */
    00163   t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL);
    00164   mean = (q15_t) __SSAT(sum, 16u);
    00165
    00166   /* Compute square of mean */
    00167   squareOfMean = ((q31_t) mean * mean) >> 15;
    00168   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
    00169
    00170   /* mean of the squares minus the square of the mean. */
    00171   in1 = (q15_t) (meanOfSquares - squareOfMean);
    00172
    00173   /* Compute standard deviation and store the result to the destination */
    00174   arm_sqrt_q15(in1, pResult);
    00175
    00176 #else
    00177
    00178   /* Run the below code for Cortex-M0 */
    00179
    00180   q63_t sumOfSquares = 0;                        /* Accumulator */
    00181   q15_t in;                                      /* input value */
    00182   /* Loop over blockSize number of values */
    00183   blkCnt = blockSize;
    00184
    00185   while(blkCnt > 0u)
    00186   {
    00187     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00188     /* Compute Sum of squares of the input samples
    00189      * and then store the result in a temporary variable, sumOfSquares. */
    00190     in = *pSrc++;
    00191     sumOfSquares += (in * in);
    00192
    00193     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00194     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00195     sum += in;
    00196
    00197     /* Decrement the loop counter */
    00198     blkCnt--;
    00199   }
    00200
    00201   /* Compute Mean of squares of the input samples
    00202    * and then store the result in a temporary variable, meanOfSquares. */
    00203   t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL);
    00204   sumOfSquares = __SSAT((sumOfSquares >> 15u), 16u);
    00205   meanOfSquares = (q31_t) ((sumOfSquares * t) >> 14u);
    00206
    00207   /* Compute mean of all input values */
    00208   mean = (q15_t) __SSAT(sum, 16u);
    00209
    00210   /* Compute square of mean of the input samples
    00211    * and then store the result in a temporary variable, squareOfMean.*/
    00212   t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL);
    00213   squareOfMean = ((q31_t) mean * mean) >> 15;
    00214   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
    00215
    00216   /* mean of the squares minus the square of the mean. */
    00217   in = (q15_t) (meanOfSquares - squareOfMean);
    00218
    00219   /* Compute standard deviation and store the result to the destination */
    00220   arm_sqrt_q15(in, pResult);
    00221
    00222 #endif /* #ifndef ARM_MATH_CM0 */
    00223
    00224
    00225 }
    00226

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