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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:        15. July 2011
    00005 * $Revision:    V1.0.10
    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/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
    00064 void arm_var_q15(
    00065   q15_t * pSrc,
    00066   uint32_t blockSize,
    00067   q31_t * pResult)
    00068 {
    00069   q63_t sum = 0;                                 /* Accumulator */
    00070   q31_t meanOfSquares, squareOfMean;             /* Mean of square and square of mean */
    00071   q15_t mean;                                    /* mean */
    00072   uint32_t blkCnt;                               /* loop counter */
    00073   q15_t t;                                       /* Temporary variable */
    00074
    00075 #ifndef ARM_MATH_CM0
    00076
    00077   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00078
    00079   q31_t in;                                      /* Input variable */
    00080   q15_t in1;                                     /* Temporary variable */
    00081   q15_t *pIn;                                    /* Temporary pointer */
    00082
    00083   pIn = pSrc;
    00084
    00085   /*loop Unrolling */
    00086   blkCnt = blockSize >> 2u;
    00087
    00088   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00089    ** a second loop below computes the remaining 1 to 3 samples. */
    00090   while(blkCnt > 0u)
    00091   {
    00092     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
    00093     /* Compute Sum of squares of the input samples
    00094      * and then store the result in a temporary variable, sum. */
    00095     in = *__SIMD32(pSrc)++;
    00096     sum = __SMLALD(in, in, sum);
    00097     in = *__SIMD32(pSrc)++;
    00098     sum = __SMLALD(in, in, sum);
    00099
    00100     /* Decrement the loop counter */
    00101     blkCnt--;
    00102   }
    00103
    00104   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00105    ** No loop unrolling is used. */
    00106   blkCnt = blockSize % 0x4u;
    00107
    00108   while(blkCnt > 0u)
    00109   {
    00110     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00111     /* Compute Sum of squares of the input samples
    00112      * and then store the result in a temporary variable, sum. */
    00113     in1 = *pSrc++;
    00114     sum = __SMLALD(in1, in1, sum);
    00115
    00116     /* Decrement the loop counter */
    00117     blkCnt--;
    00118   }
    00119
    00120   /* Compute Mean of squares of the input samples
    00121    * and then store the result in a temporary variable, meanOfSquares. */
    00122   t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
    00123   sum = __SSAT((sum >> 15u), 16u);
    00124
    00125   meanOfSquares = (q31_t) ((sum * t) >> 14u);
    00126
    00127   /* Reset the accumulator */
    00128   sum = 0;
    00129
    00130   /*loop Unrolling */
    00131   blkCnt = blockSize >> 2u;
    00132
    00133   /* Reset the input working pointer */
    00134   pSrc = pIn;
    00135
    00136   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
    00137    ** a second loop below computes the remaining 1 to 3 samples. */
    00138   while(blkCnt > 0u)
    00139   {
    00140     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00141     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00142     sum += *pSrc++;
    00143     sum += *pSrc++;
    00144     sum += *pSrc++;
    00145     sum += *pSrc++;
    00146
    00147     /* Decrement the loop counter */
    00148     blkCnt--;
    00149   }
    00150
    00151   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
    00152    ** No loop unrolling is used. */
    00153   blkCnt = blockSize % 0x4u;
    00154
    00155   while(blkCnt > 0u)
    00156   {
    00157     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00158     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00159     sum += *pSrc++;
    00160
    00161     /* Decrement the loop counter */
    00162     blkCnt--;
    00163   }
    00164
    00165 #else
    00166
    00167   /* Run the below code for Cortex-M0 */
    00168
    00169   q63_t sumOfSquares = 0;                        /* Accumulator */
    00170   q15_t in;                                      /* Temporary variable */
    00171   /* Loop over blockSize number of values */
    00172   blkCnt = blockSize;
    00173
    00174   while(blkCnt > 0u)
    00175   {
    00176     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
    00177     /* Compute Sum of squares of the input samples
    00178      * and then store the result in a temporary variable, sumOfSquares. */
    00179     in = *pSrc++;
    00180     sumOfSquares += (in * in);
    00181
    00182     /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
    00183     /* Compute sum of all input values and then store the result in a temporary variable, sum. */
    00184     sum += in;
    00185
    00186     /* Decrement the loop counter */
    00187     blkCnt--;
    00188   }
    00189
    00190   /* Compute Mean of squares of the input samples
    00191    * and then store the result in a temporary variable, meanOfSquares. */
    00192   t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
    00193   sumOfSquares = __SSAT((sumOfSquares >> 15u), 16u);
    00194   meanOfSquares = (q31_t) ((sumOfSquares * t) >> 14u);
    00195
    00196
    00197 #endif /* #ifndef ARM_MATH_CM0 */
    00198
    00199   /* Compute mean of all input values */
    00200   t = (q15_t) ((1.0f / (float32_t) (blockSize * (blockSize - 1u))) * 32768);
    00201   mean = __SSAT(sum, 16u);
    00202
    00203   /* Compute square of mean */
    00204   squareOfMean = ((q31_t) mean * mean) >> 15;
    00205   squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
    00206
    00207   /* Compute variance and then store the result to the destination */
    00208   *pResult = (meanOfSquares - squareOfMean);
    00209
    00210 }
    00211

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