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/* ----------------------------------------------------------------------
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* Copyright (C) 2010 ARM Limited. All rights reserved.
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*
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* $Date: 15. July 2011
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* $Revision: V1.0.10
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*
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* Project: CMSIS DSP Library
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* Title: arm_var_q15.c
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*
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* Description: Variance of an array of Q15 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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* Version 1.0.10 2011/7/15
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* Big Endian support added and Merged M0 and M3/M4 Source code.
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*
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* Version 1.0.3 2010/11/29
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* Re-organized the CMSIS folders and updated documentation.
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*
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* Version 1.0.2 2010/11/11
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* Documentation updated.
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*
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* Version 1.0.1 2010/10/05
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* Production release and review comments incorporated.
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*
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* Version 1.0.0 2010/09/20
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* Production release and review comments incorporated.
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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 variance
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* @{
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*/
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/**
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* @brief Variance of the elements of a Q15 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 variance value returned here
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* @return none.
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*
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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 a 64-bit internal accumulator.
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* The input is represented in 1.15 format.
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* Intermediate multiplication yields a 2.30 format, and this
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* result is added without saturation to a 64-bit accumulator in 34.30 format.
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* With 33 guard bits in the accumulator, there is no risk of overflow, and the
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* full precision of the intermediate multiplication is preserved.
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* Finally, the 34.30 result is truncated to 34.15 format by discarding the lower
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* 15 bits, and then saturated to yield a result in 1.15 format.
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*
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*/
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void arm_var_q15(
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q15_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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q31_t meanOfSquares, squareOfMean; /* Mean of square and square of mean */
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q15_t mean; /* mean */
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uint32_t blkCnt; /* loop counter */
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q15_t t; /* Temporary variable */
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#ifndef ARM_MATH_CM0
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/* Run the below code for Cortex-M4 and Cortex-M3 */
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q31_t in; /* Input variable */
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q15_t in1; /* Temporary variable */
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q15_t *pIn; /* Temporary pointer */
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pIn = pSrc;
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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 = *__SIMD32(pSrc)++;
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sum = __SMLALD(in, in, sum);
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in = *__SIMD32(pSrc)++;
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sum = __SMLALD(in, in, sum);
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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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in1 = *pSrc++;
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sum = __SMLALD(in1, in1, sum);
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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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t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
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sum = __SSAT((sum >> 15u), 16u);
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meanOfSquares = (q31_t) ((sum * t) >> 14u);
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/* Reset the accumulator */
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sum = 0;
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/*loop Unrolling */
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blkCnt = blockSize >> 2u;
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/* Reset the input working pointer */
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pSrc = pIn;
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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[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 += *pSrc++;
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sum += *pSrc++;
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sum += *pSrc++;
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sum += *pSrc++;
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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[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 += *pSrc++;
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/* Decrement the loop counter */
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blkCnt--;
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}
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#else
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/* Run the below code for Cortex-M0 */
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q63_t sumOfSquares = 0; /* Accumulator */
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q15_t in; /* Temporary variable */
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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++;
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sumOfSquares += (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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t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
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sumOfSquares = __SSAT((sumOfSquares >> 15u), 16u);
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meanOfSquares = (q31_t) ((sumOfSquares * t) >> 14u);
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#endif /* #ifndef ARM_MATH_CM0 */
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/* Compute mean of all input values */
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t = (q15_t) ((1.0f / (float32_t) (blockSize * (blockSize - 1u))) * 32768);
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mean = __SSAT(sum, 16u);
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/* Compute square of mean */
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squareOfMean = ((q31_t) mean * mean) >> 15;
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squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
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/* Compute variance and then store the result to the destination */
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*pResult = (meanOfSquares - squareOfMean);
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}
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/**
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* @} end of variance group
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*/
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