173 lines
3.9 KiB
C
173 lines
3.9 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_var_f32.c
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* Description: Variance of the elements of a floating-point vector
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*
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* $Date: 18. March 2019
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* $Revision: V1.6.0
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the License); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an AS IS BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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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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@defgroup variance Variance
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Calculates the variance of the elements in the input vector.
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The underlying algorithm used is the direct method sometimes referred to as the two-pass method:
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<pre>
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Result = sum(element - meanOfElements)^2) / numElement - 1
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meanOfElements = ( pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] ) / blockSize
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</pre>
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There are separate functions for floating point, Q31, and Q15 data types.
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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 floating-point vector.
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@param[in] pSrc points to the input vector
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@param[in] blockSize number of samples in 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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void arm_var_f32(
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const float32_t * pSrc,
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uint32_t blockSize,
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float32_t * pResult)
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{
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uint32_t blkCnt; /* Loop counter */
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float32_t sum = 0.0f; /* Temporary result storage */
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float32_t fSum = 0.0f;
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float32_t fMean, fValue;
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const float32_t * pInput = pSrc;
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if (blockSize <= 1U)
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{
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*pResult = 0;
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return;
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}
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 outputs at a time */
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blkCnt = blockSize >> 2U;
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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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sum += *pInput++;
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sum += *pInput++;
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sum += *pInput++;
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sum += *pInput++;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining outputs */
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blkCnt = blockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of samples */
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blkCnt = blockSize;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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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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sum += *pInput++;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize */
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fMean = sum / (float32_t) blockSize;
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pInput = pSrc;
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Loop unrolling: Compute 4 outputs at a time */
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blkCnt = blockSize >> 2U;
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while (blkCnt > 0U)
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{
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fValue = *pInput++ - fMean;
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fSum += fValue * fValue;
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fValue = *pInput++ - fMean;
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fSum += fValue * fValue;
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fValue = *pInput++ - fMean;
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fSum += fValue * fValue;
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fValue = *pInput++ - fMean;
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fSum += fValue * fValue;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Loop unrolling: Compute remaining outputs */
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blkCnt = blockSize % 0x4U;
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#else
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/* Initialize blkCnt with number of samples */
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blkCnt = blockSize;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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while (blkCnt > 0U)
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{
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fValue = *pInput++ - fMean;
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fSum += fValue * fValue;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Variance */
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*pResult = fSum / (float32_t)(blockSize - 1.0f);
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}
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/**
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@} end of variance group
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*/
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