119 lines
3.6 KiB
C
119 lines
3.6 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_rms_q31.c
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* Description: Root Mean Square of the elements of a Q31 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 RMS
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@{
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*/
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/**
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@brief Root Mean Square of the elements of a Q31 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 root mean square 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 an internal 64-bit
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accumulator. The input is represented in 1.31 format, and intermediate
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multiplication yields a 2.62 format. The accumulator maintains full precision
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of the intermediate multiplication results, but provides only a single guard
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bit. There is no saturation on intermediate additions. If the accumulator
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overflows, it wraps around and distorts the result. In order to avoid
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overflows completely, the input signal must be scaled down by log2(blockSize)
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bits, as a total of blockSize additions are performed internally. Finally,
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the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.
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*/
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void arm_rms_q31(const q31_t *pSrc, uint32_t blockSize, q31_t *pResult) {
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uint32_t blkCnt; /* Loop counter */
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uint64_t sum = 0; /* Temporary result storage (can get never negative. changed
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type from q63 to uint64 */
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q31_t in; /* Temporary variable to store input value */
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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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/* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-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, sum. */
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sum += ((q63_t)in * in);
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in = *pSrc++;
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sum += ((q63_t)in * in);
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in = *pSrc++;
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sum += ((q63_t)in * in);
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in = *pSrc++;
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sum += ((q63_t)in * in);
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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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/* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-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. */
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sum += ((q63_t)in * in);
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/* Decrement loop counter */
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blkCnt--;
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}
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/* Convert data in 2.62 to 1.31 by 31 right shifts and saturate */
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/* Compute Rms and store result in destination vector */
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arm_sqrt_q31(clip_q63_to_q31((sum / (q63_t)blockSize) >> 31), pResult);
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}
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/**
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@} end of RMS group
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*/
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