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Rev	Author	Line No.	Line
2	mjames	1	/* ----------------------------------------------------------------------
		2	* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
		3	*
		4	* $Date: 19. March 2015
		5	* $Revision: V.1.4.5
		6	*
		7	* Project: CMSIS DSP Library
		8	* Title: arm_rms_q15.c
		9	*
		10	* Description: Root Mean Square of the elements of a Q15 vector.
		11	*
		12	* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
		13	*
		14	* Redistribution and use in source and binary forms, with or without
		15	* modification, are permitted provided that the following conditions
		16	* are met:
		17	* - Redistributions of source code must retain the above copyright
		18	* notice, this list of conditions and the following disclaimer.
		19	* - Redistributions in binary form must reproduce the above copyright
		20	* notice, this list of conditions and the following disclaimer in
		21	* the documentation and/or other materials provided with the
		22	* distribution.
		23	* - Neither the name of ARM LIMITED nor the names of its contributors
		24	* may be used to endorse or promote products derived from this
		25	* software without specific prior written permission.
		26	*
		27	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
		28	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
		29	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
		30	* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
		31	* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
		32	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
		33	* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
		34	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
		35	* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
		36	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
		37	* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
		38	* POSSIBILITY OF SUCH DAMAGE.
		39	* ---------------------------------------------------------------------------- */
		40
		41	#include "arm_math.h"
		42
		43	/**
		44	* @addtogroup RMS
		45	* @{
		46	*/
		47
		48	/**
		49	* @brief Root Mean Square of the elements of a Q15 vector.
		50	* @param[in] *pSrc points to the input vector
		51	* @param[in] blockSize length of the input vector
		52	* @param[out] *pResult rms value returned here
		53	* @return none.
		54	*
		55	* @details
		56	* <b>Scaling and Overflow Behavior:</b>
		57	*
		58	* \par
		59	* The function is implemented using a 64-bit internal accumulator.
		60	* The input is represented in 1.15 format.
		61	* Intermediate multiplication yields a 2.30 format, and this
		62	* result is added without saturation to a 64-bit accumulator in 34.30 format.
		63	* With 33 guard bits in the accumulator, there is no risk of overflow, and the
		64	* full precision of the intermediate multiplication is preserved.
		65	* Finally, the 34.30 result is truncated to 34.15 format by discarding the lower
		66	* 15 bits, and then saturated to yield a result in 1.15 format.
		67	*
		68	*/
		69
		70	void arm_rms_q15(
		71	q15_t * pSrc,
		72	uint32_t blockSize,
		73	q15_t * pResult)
		74	{
		75	q63_t sum = 0; /* accumulator */
		76
		77	#ifndef ARM_MATH_CM0_FAMILY
		78
		79	/* Run the below code for Cortex-M4 and Cortex-M3 */
		80
		81	q31_t in; /* temporary variable to store the input value */
		82	q15_t in1; /* temporary variable to store the input value */
		83	uint32_t blkCnt; /* loop counter */
		84
		85	/* loop Unrolling */
		86	blkCnt = blockSize >> 2u;
		87
		88	/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
		89	** a second loop below computes the remaining 1 to 3 samples. */
		90	while(blkCnt > 0u)
		91	{
		92	/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		93	/* Compute sum of the squares and then store the results in a temporary variable, sum */
		94	in = *__SIMD32(pSrc)++;
		95	sum = __SMLALD(in, in, sum);
		96	in = *__SIMD32(pSrc)++;
		97	sum = __SMLALD(in, in, sum);
		98
		99	/* Decrement the loop counter */
		100	blkCnt--;
		101	}
		102
		103	/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
		104	** No loop unrolling is used. */
		105	blkCnt = blockSize % 0x4u;
		106
		107	while(blkCnt > 0u)
		108	{
		109	/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		110	/* Compute sum of the squares and then store the results in a temporary variable, sum */
		111	in1 = *pSrc++;
		112	sum = __SMLALD(in1, in1, sum);
		113
		114	/* Decrement the loop counter */
		115	blkCnt--;
		116	}
		117
		118	/* Truncating and saturating the accumulator to 1.15 format */
		119	/* Store the result in the destination */
		120	arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult);
		121
		122	#else
		123
		124	/* Run the below code for Cortex-M0 */
		125
		126	q15_t in; /* temporary variable to store the input value */
		127	uint32_t blkCnt; /* loop counter */
		128
		129	/* Loop over blockSize number of values */
		130	blkCnt = blockSize;
		131
		132	while(blkCnt > 0u)
		133	{
		134	/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		135	/* Compute sum of the squares and then store the results in a temporary variable, sum */
		136	in = *pSrc++;
		137	sum += ((q31_t) in * in);
		138
		139	/* Decrement the loop counter */
		140	blkCnt--;
		141	}
		142
		143	/* Truncating and saturating the accumulator to 1.15 format */
		144	/* Store the result in the destination */
		145	arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult);
		146
		147	#endif /* #ifndef ARM_MATH_CM0_FAMILY */
		148
		149	}
		150
		151	/**
		152	* @} end of RMS group
		153	*/

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