144 lines
4.5 KiB
C
144 lines
4.5 KiB
C
/* ----------------------------------------------------------------------
|
|
* Project: CMSIS DSP Library
|
|
* Title: arm_std_q31.c
|
|
* Description: Standard deviation of the elements of a Q31 vector
|
|
*
|
|
* $Date: 18. March 2019
|
|
* $Revision: V1.6.0
|
|
*
|
|
* Target Processor: Cortex-M cores
|
|
* -------------------------------------------------------------------- */
|
|
/*
|
|
* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
|
|
*
|
|
* SPDX-License-Identifier: Apache-2.0
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the License); you may
|
|
* not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at
|
|
*
|
|
* www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an AS IS BASIS, WITHOUT
|
|
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
|
|
#include "arm_math.h"
|
|
|
|
/**
|
|
@ingroup groupStats
|
|
*/
|
|
|
|
/**
|
|
@addtogroup STD
|
|
@{
|
|
*/
|
|
|
|
/**
|
|
@brief Standard deviation of the elements of a Q31 vector.
|
|
@param[in] pSrc points to the input vector.
|
|
@param[in] blockSize number of samples in input vector.
|
|
@param[out] pResult standard deviation value returned here.
|
|
@return none
|
|
|
|
@par Scaling and Overflow Behavior
|
|
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_std_q31(const q31_t *pSrc, uint32_t blockSize, q31_t *pResult) {
|
|
uint32_t blkCnt; /* Loop counter */
|
|
q63_t sum = 0; /* Accumulator */
|
|
q63_t meanOfSquares, squareOfMean; /* Square of mean and mean of square */
|
|
q63_t sumOfSquares = 0; /* Sum of squares */
|
|
q31_t in; /* Temporary variable to store input value */
|
|
|
|
if (blockSize <= 1U) {
|
|
*pResult = 0;
|
|
return;
|
|
}
|
|
|
|
#if defined(ARM_MATH_LOOPUNROLL)
|
|
|
|
/* Loop unrolling: Compute 4 outputs at a time */
|
|
blkCnt = blockSize >> 2U;
|
|
|
|
while (blkCnt > 0U) {
|
|
/* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
|
|
/* C = A[0] + A[1] + ... + A[blockSize-1] */
|
|
|
|
in = *pSrc++ >> 8U;
|
|
/* Compute sum of squares and store result in a temporary variable,
|
|
* sumOfSquares. */
|
|
sumOfSquares += ((q63_t)(in) * (in));
|
|
/* Compute sum and store result in a temporary variable, sum. */
|
|
sum += in;
|
|
|
|
in = *pSrc++ >> 8U;
|
|
sumOfSquares += ((q63_t)(in) * (in));
|
|
sum += in;
|
|
|
|
in = *pSrc++ >> 8U;
|
|
sumOfSquares += ((q63_t)(in) * (in));
|
|
sum += in;
|
|
|
|
in = *pSrc++ >> 8U;
|
|
sumOfSquares += ((q63_t)(in) * (in));
|
|
sum += in;
|
|
|
|
/* Decrement loop counter */
|
|
blkCnt--;
|
|
}
|
|
|
|
/* Loop unrolling: Compute remaining outputs */
|
|
blkCnt = blockSize % 0x4U;
|
|
|
|
#else
|
|
|
|
/* Initialize blkCnt with number of samples */
|
|
blkCnt = blockSize;
|
|
|
|
#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
|
|
|
|
while (blkCnt > 0U) {
|
|
/* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
|
|
/* C = A[0] + A[1] + ... + A[blockSize-1] */
|
|
|
|
in = *pSrc++ >> 8U;
|
|
/* Compute sum of squares and store result in a temporary variable,
|
|
* sumOfSquares. */
|
|
sumOfSquares += ((q63_t)(in) * (in));
|
|
/* Compute sum and store result in a temporary variable, sum. */
|
|
sum += in;
|
|
|
|
/* Decrement loop counter */
|
|
blkCnt--;
|
|
}
|
|
|
|
/* Compute Mean of squares and store result in a temporary variable,
|
|
* meanOfSquares. */
|
|
meanOfSquares = (sumOfSquares / (q63_t)(blockSize - 1U));
|
|
|
|
/* Compute square of mean */
|
|
squareOfMean = (sum * sum / (q63_t)(blockSize * (blockSize - 1U)));
|
|
|
|
/* Compute standard deviation and store result in destination */
|
|
arm_sqrt_q31((meanOfSquares - squareOfMean) >> 15U, pResult);
|
|
}
|
|
|
|
/**
|
|
@} end of STD group
|
|
*/
|