161 lines
5 KiB
C
161 lines
5 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_std_q15.c
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* Description: Standard deviation of an array of Q15 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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@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 Q15 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 standard deviation value returned here
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@return none
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@par Scaling and Overflow Behavior
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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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void arm_std_q15(
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const q15_t * pSrc,
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uint32_t blockSize,
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q15_t * pResult)
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{
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uint32_t blkCnt; /* Loop counter */
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q31_t sum = 0; /* Accumulator */
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q31_t meanOfSquares, squareOfMean; /* Square of mean and mean of square */
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q63_t sumOfSquares = 0; /* Sum of squares */
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q15_t in; /* Temporary variable to store input value */
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#if defined (ARM_MATH_LOOPUNROLL) && defined (ARM_MATH_DSP)
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q31_t in32; /* Temporary variable to store input value */
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#endif
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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[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
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/* C = A[0] + A[1] + ... + A[blockSize-1] */
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/* Compute sum of squares and store result in a temporary variable, sumOfSquares. */
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/* Compute sum and store result in a temporary variable, sum. */
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#if defined (ARM_MATH_DSP)
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in32 = read_q15x2_ia ((q15_t **) &pSrc);
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sumOfSquares = __SMLALD(in32, in32, sumOfSquares);
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sum += ((in32 << 16U) >> 16U);
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sum += (in32 >> 16U);
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in32 = read_q15x2_ia ((q15_t **) &pSrc);
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sumOfSquares = __SMLALD(in32, in32, sumOfSquares);
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sum += ((in32 << 16U) >> 16U);
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sum += (in32 >> 16U);
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#else
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in = *pSrc++;
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sumOfSquares += (in * in);
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sum += in;
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in = *pSrc++;
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sumOfSquares += (in * in);
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sum += in;
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in = *pSrc++;
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sumOfSquares += (in * in);
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sum += in;
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in = *pSrc++;
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sumOfSquares += (in * in);
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sum += in;
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#endif /* #if defined (ARM_MATH_DSP) */
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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[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
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/* C = A[0] + A[1] + ... + A[blockSize-1] */
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in = *pSrc++;
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/* Compute sum of squares and store result in a temporary variable, sumOfSquares. */
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sumOfSquares += (in * in);
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/* Compute sum and store result in a temporary variable, sum. */
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sum += in;
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Compute Mean of squares and store result in a temporary variable, meanOfSquares. */
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meanOfSquares = (q31_t) (sumOfSquares / (q63_t)(blockSize - 1U));
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/* Compute square of mean */
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squareOfMean = (q31_t) ((q63_t) sum * sum / (q63_t)(blockSize * (blockSize - 1U)));
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/* mean of squares minus the square of mean. */
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/* Compute standard deviation and store result in destination */
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arm_sqrt_q15(__SSAT((meanOfSquares - squareOfMean) >> 15U, 16U), 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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