CMSIS DSP library

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Dependents:
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performance_timer
Surfboard_
gps2rtty
Capstone
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#### Legacy Warning

This is an mbed 2 library. To learn more about mbed OS 5, visit the docs.

## cmsis_dsp/StatisticsFunctions/arm_var_q31.c

- Committer:
- mbed_official
- Date:
- 2015-11-20
- Revision:
**5:3762170b6d4d**- Parent:
- 3:7a284390b0ce

### File content as of revision 5:3762170b6d4d:

/* ---------------------------------------------------------------------- * Copyright (C) 2010-2014 ARM Limited. All rights reserved. * * $Date: 19. March 2015 * $Revision: V.1.4.5 * * 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, which is then downshifted by 8 bits * which yields 1.23, and intermediate multiplication yields a 2.46 format. * The accumulator maintains full precision of the intermediate multiplication results, * but provides only a 16 guard bits. * 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)-8 bits, as a total of blockSize additions are performed internally. * After division, internal variables should be Q18.46 * Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value. * */ void arm_var_q31( q31_t * pSrc, uint32_t blockSize, q31_t * pResult) { q63_t sum = 0; /* Accumulator */ q63_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ q31_t in; /* input value */ uint32_t blkCnt; /* loop counter */ q63_t sumOfSquares = 0; /* Accumulator */ if(blockSize == 1) { *pResult = 0; return; } #ifndef ARM_MATH_CM0_FAMILY /* Run the below code for Cortex-M4 and Cortex-M3 */ /*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. */ in = *pSrc++ >> 8; sum += in; sumOfSquares += ((q63_t) (in) * (in)); in = *pSrc++ >> 8; sum += in; sumOfSquares += ((q63_t) (in) * (in)); in = *pSrc++ >> 8; sum += in; sumOfSquares += ((q63_t) (in) * (in)); in = *pSrc++ >> 8; sum += in; sumOfSquares += ((q63_t) (in) * (in)); /* Decrement the loop counter */ blkCnt--; } /* If the blockSize is not a multiple of 4, compute any remaining output samples here. ** No loop unrolling is used. */ blkCnt = blockSize % 0x4u; 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++ >> 8; sum += in; sumOfSquares += ((q63_t) (in) * (in)); /* Decrement the loop counter */ blkCnt--; } /* Compute Mean of squares of the input samples * and then store the result in a temporary variable, meanOfSquares. */ meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1); #else /* Run the below code for Cortex-M0 */ /* Loop over blockSize number of values */ blkCnt = blockSize; 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, sumOfSquares. */ in = *pSrc++ >> 8; sumOfSquares += ((q63_t) (in) * (in)); /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ /* Compute sum of all input values and then store the result in a temporary variable, sum. */ sum += in; /* Decrement the loop counter */ blkCnt--; } /* Compute Mean of squares of the input samples * and then store the result in a temporary variable, meanOfSquares. */ meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1); #endif /* #ifndef ARM_MATH_CM0_FAMILY */ /* Compute square of mean */ squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1u)); /* Compute standard deviation and then store the result to the destination */ *pResult = (meanOfSquares - squareOfMean) >> 15; } /** * @} end of variance group */