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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: 29. November 2010
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* $Revision: V1.0.3
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*
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* Project: CMSIS DSP Library
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* Title: arm_rms_q31.c
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*
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* Description: root mean square value of an array of Q31 type
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*
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* Target Processor: Cortex-M4/Cortex-M3
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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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* @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 length of the input vector
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* @param[out] *pResult rms 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 an internal 64-bit accumulator.
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* The input is represented in 1.31 format, and intermediate multiplication
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* yields a 2.62 format.
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* The accumulator maintains full precision of the intermediate multiplication results,
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* but provides only a single guard bit.
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* There is no saturation on intermediate additions.
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* If the accumulator overflows, it wraps around and distorts the result.
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* In order to avoid overflows completely, the input signal must be scaled down by
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* log2(blockSize) bits, as a total of blockSize additions are performed internally.
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* Finally, 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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*/
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void arm_rms_q31(
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q31_t * pSrc,
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uint32_t blockSize,
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q31_t * pResult)
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{
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q31_t *pIn1 = pSrc; /* SrcA pointer */
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q63_t sum = 0; /* accumulator */
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q31_t in; /* Temporary variable to store the input */
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uint32_t blkCnt; /* loop counter */
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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[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
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/* Compute sum of the squares and then store the result in a temporary variable, sum */
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in = *pIn1++;
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sum += (q63_t) in *in;
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in = *pIn1++;
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sum += (q63_t) in *in;
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in = *pIn1++;
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sum += (q63_t) in *in;
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in = *pIn1++;
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sum += (q63_t) in *in;
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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[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
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/* Compute sum of the squares and then store the results in a temporary variable, sum */
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in = *pIn1++;
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sum += (q63_t) in *in;
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/* Decrement the 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 */
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sum = sum >> 31;
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/* Compute Rms and store the result in the destination vector */
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arm_sqrt_q31((q31_t) (sum / (int32_t) blockSize), 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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