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186 lines
6.4 KiB
186 lines
6.4 KiB
/* ----------------------------------------------------------------------
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* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
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*
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* $Date: 12. March 2014
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* $Revision: V1.4.4
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*
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* Project: CMSIS DSP Library
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* Title: arm_std_q31.c
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*
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* Description: Standard deviation of an array of Q31 type.
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*
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* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* - Neither the name of ARM LIMITED nor the names of its contributors
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* may be used to endorse or promote products derived from this
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* software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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* -------------------------------------------------------------------- */
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#include "arm_math.h"
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/**
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* @ingroup groupStats
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*/
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/**
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* @addtogroup STD
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* @{
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*/
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/**
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* @brief Standard deviation of the elements of a Q31 vector.
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* @param[in] *pSrc points to the input vector
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* @param[in] blockSize length of the input vector
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* @param[out] *pResult standard deviation value returned here
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* @return none.
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* @details
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* <b>Scaling and Overflow Behavior:</b>
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*
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*\par
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* The function is implemented using an internal 64-bit accumulator.
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* The input is represented in 1.31 format, which is then downshifted by 8 bits
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* which yields 1.23, and intermediate multiplication yields a 2.46 format.
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* The accumulator maintains full precision of the intermediate multiplication results,
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* but provides only a 16 guard bits.
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* There is no saturation on intermediate additions.
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* If the accumulator overflows it wraps around and distorts the result.
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* In order to avoid overflows completely the input signal must be scaled down by
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* log2(blockSize)-8 bits, as a total of blockSize additions are performed internally.
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* After division, internal variables should be Q18.46
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* Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value.
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*
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*/
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void arm_std_q31(
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q31_t * pSrc,
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uint32_t blockSize,
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q31_t * pResult)
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{
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q63_t sum = 0; /* Accumulator */
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q63_t meanOfSquares, squareOfMean; /* square of mean and mean of square */
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q31_t in; /* input value */
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uint32_t blkCnt; /* loop counter */
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q63_t sumOfSquares = 0; /* Accumulator */
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if(blockSize == 1)
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{
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*pResult = 0;
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return;
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}
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#ifndef ARM_MATH_CM0_FAMILY
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/* Run the below code for Cortex-M4 and Cortex-M3 */
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/*loop Unrolling */
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blkCnt = blockSize >> 2u;
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/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
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** a second loop below computes the remaining 1 to 3 samples. */
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while(blkCnt > 0u)
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{
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/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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/* Compute Sum of squares of the input samples
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* and then store the result in a temporary variable, sum. */
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in = *pSrc++ >> 8;
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sum += in;
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sumOfSquares += ((q63_t) (in) * (in));
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in = *pSrc++ >> 8;
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sum += in;
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sumOfSquares += ((q63_t) (in) * (in));
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in = *pSrc++ >> 8;
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sum += in;
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sumOfSquares += ((q63_t) (in) * (in));
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in = *pSrc++ >> 8;
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sum += in;
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sumOfSquares += ((q63_t) (in) * (in));
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/* Decrement the loop counter */
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blkCnt--;
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}
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/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
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** No loop unrolling is used. */
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blkCnt = blockSize % 0x4u;
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while(blkCnt > 0u)
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{
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/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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/* Compute Sum of squares of the input samples
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* and then store the result in a temporary variable, sum. */
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in = *pSrc++ >> 8;
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sum += in;
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sumOfSquares += ((q63_t) (in) * (in));
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/* Decrement the loop counter */
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blkCnt--;
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}
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/* Compute Mean of squares of the input samples
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* and then store the result in a temporary variable, meanOfSquares. */
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meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1);
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#else
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/* Run the below code for Cortex-M0 */
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/* Loop over blockSize number of values */
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blkCnt = blockSize;
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while(blkCnt > 0u)
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{
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/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
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/* Compute Sum of squares of the input samples
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* and then store the result in a temporary variable, sumOfSquares. */
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in = *pSrc++ >> 8;
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sumOfSquares += ((q63_t) (in) * (in));
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/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
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/* Compute sum of all input values and then store the result in a temporary variable, sum. */
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sum += in;
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/* Decrement the loop counter */
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blkCnt--;
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}
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/* Compute Mean of squares of the input samples
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* and then store the result in a temporary variable, meanOfSquares. */
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meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1);
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#endif /* #ifndef ARM_MATH_CM0_FAMILY */
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/* Compute square of mean */
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squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1u));
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/* Compute standard deviation and then store the result to the destination */
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arm_sqrt_q31((meanOfSquares - squareOfMean) >> 15, pResult);
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}
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/**
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* @} end of STD group
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*/
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