+++ /dev/null
-/* ----------------------------------------------------------------------
-* Copyright (C) 2010-2013 ARM Limited. All rights reserved.
-*
-* $Date: 17. January 2013
-* $Revision: V1.4.1
-*
-* Project: CMSIS DSP Library
-* Title: arm_var_q31.c
-*
-* Description: Variance of an array of Q31 type.
-*
-* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
-*
-* Redistribution and use in source and binary forms, with or without
-* modification, are permitted provided that the following conditions
-* are met:
-* - Redistributions of source code must retain the above copyright
-* notice, this list of conditions and the following disclaimer.
-* - Redistributions in binary form must reproduce the above copyright
-* notice, this list of conditions and the following disclaimer in
-* the documentation and/or other materials provided with the
-* distribution.
-* - Neither the name of ARM LIMITED nor the names of its contributors
-* may be used to endorse or promote products derived from this
-* software without specific prior written permission.
-*
-* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
-* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
-* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
-* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
-* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
-* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
-* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-* POSSIBILITY OF SUCH DAMAGE.
-* -------------------------------------------------------------------- */
-
-#include "arm_math.h"
-
-/**
- * @ingroup groupStats
- */
-
-/**
- * @addtogroup variance
- * @{
- */
-
-/**
- * @brief Variance of the elements of a Q31 vector.
- * @param[in] *pSrc points to the input vector
- * @param[in] blockSize length of the input vector
- * @param[out] *pResult variance value returned here
- * @return none.
- *
- * @details
- * <b>Scaling and Overflow Behavior:</b>
- *
- *\par
- * The function is implemented using an internal 64-bit accumulator.
- * The input is represented in 1.31 format, and intermediate multiplication
- * yields a 2.62 format.
- * The accumulator maintains full precision of the intermediate multiplication results,
- * but provides only a single guard bit.
- * There is no saturation on intermediate additions.
- * If the accumulator overflows it wraps around and distorts the result.
- * In order to avoid overflows completely the input signal must be scaled down by
- * log2(blockSize) bits, as a total of blockSize additions are performed internally.
- * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.
- *
- */
-
-
-void arm_var_q31(
- q31_t * pSrc,
- uint32_t blockSize,
- q63_t * pResult)
-{
- q63_t sum = 0, sumSquare = 0; /* Accumulator */
- q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */
- q31_t mean; /* mean */
- q31_t in; /* input value */
- q31_t t; /* Temporary variable */
- uint32_t blkCnt; /* loop counter */
-
-#ifndef ARM_MATH_CM0_FAMILY
-
- /* Run the below code for Cortex-M4 and Cortex-M3 */
- q63_t sumSquare1 = 0; /* Accumulator */
- q31_t in1, in2, in3, in4; /* Temporary input variables */
-
- /*loop Unrolling */
- blkCnt = blockSize >> 2u;
-
- /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
- ** a second loop below computes the remaining 1 to 3 samples. */
- while(blkCnt > 0u)
- {
- /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
- /* Compute Sum of squares of the input samples
- * and then store the result in a temporary variable, sum. */
- /* read input samples from source buffer */
- in1 = pSrc[0];
- in2 = pSrc[1];
-
- /* calculate sum of inputs */
- sum += in1;
- /* calculate sum of squares */
- sumSquare += ((q63_t) (in1) * (in1));
- in3 = pSrc[2];
- sum += in2;
- sumSquare1 += ((q63_t) (in2) * (in2));
- in4 = pSrc[3];
- sum += in3;
- sumSquare += ((q63_t) (in3) * (in3));
- sum += in4;
- sumSquare1 += ((q63_t) (in4) * (in4));
-
- /* update input pointer to process next samples */
- pSrc += 4u;
-
- /* Decrement the loop counter */
- blkCnt--;
- }
-
- /* add two accumulators */
- sumSquare = sumSquare + sumSquare1;
-
- /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
- ** No loop unrolling is used. */
- blkCnt = blockSize % 0x4u;
-
-#else
-
- /* Run the below code for Cortex-M0 */
- blkCnt = blockSize;
-
-#endif /* #ifndef ARM_MATH_CM0_FAMILY */
-
- while(blkCnt > 0u)
- {
- /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
- /* Compute Sum of squares of the input samples
- * and then store the result in a temporary variable, sum. */
- in = *pSrc++;
- sumSquare += ((q63_t) (in) * (in));
- sum += in;
-
- /* Decrement the loop counter */
- blkCnt--;
- }
-
- t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
-
- /* Compute Mean of squares of the input samples
- * and then store the result in a temporary variable, meanOfSquares. */
- sumSquare = (sumSquare >> 31);
- meanOfSquares = (q31_t) ((sumSquare * t) >> 30);
-
- /* Compute mean of all input values */
- t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f);
- mean = (q31_t) (sum);
-
- /* Compute square of mean */
- squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
- squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
-
- /* Compute variance and then store the result to the destination */
- *pResult = (q63_t) meanOfSquares - squareOfMean;
-
-}
-
-/**
- * @} end of variance group
- */
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