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src/Cortex-M4-M3/StatisticsFunctions/arm_std_q15.c@0:1014af42efd9, 2011-03-10 (annotated)

Committer:: simon
Date:: Thu Mar 10 15:07:50 2011 +0000
Revision:: 0:1014af42efd9

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User	Revision	Line number	New contents of line
simon	0:1014af42efd9	1	/* ----------------------------------------------------------------------
simon	0:1014af42efd9	2	* Copyright (C) 2010 ARM Limited. All rights reserved.
simon	0:1014af42efd9	3	*
simon	0:1014af42efd9	4	* $Date: 29. November 2010
simon	0:1014af42efd9	5	* $Revision: V1.0.3
simon	0:1014af42efd9	6	*
simon	0:1014af42efd9	7	* Project: CMSIS DSP Library
simon	0:1014af42efd9	8	* Title: arm_std_q15.c
simon	0:1014af42efd9	9	*
simon	0:1014af42efd9	10	* Description: Standard deviation of an array of Q15 type.
simon	0:1014af42efd9	11	*
simon	0:1014af42efd9	12	* Target Processor: Cortex-M4/Cortex-M3
simon	0:1014af42efd9	13	*
simon	0:1014af42efd9	14	* Version 1.0.3 2010/11/29
simon	0:1014af42efd9	15	* Re-organized the CMSIS folders and updated documentation.
simon	0:1014af42efd9	16	*
simon	0:1014af42efd9	17	* Version 1.0.2 2010/11/11
simon	0:1014af42efd9	18	* Documentation updated.
simon	0:1014af42efd9	19	*
simon	0:1014af42efd9	20	* Version 1.0.1 2010/10/05
simon	0:1014af42efd9	21	* Production release and review comments incorporated.
simon	0:1014af42efd9	22	*
simon	0:1014af42efd9	23	* Version 1.0.0 2010/09/20
simon	0:1014af42efd9	24	* Production release and review comments incorporated.
simon	0:1014af42efd9	25	* -------------------------------------------------------------------- */
simon	0:1014af42efd9	26
simon	0:1014af42efd9	27	#include "arm_math.h"
simon	0:1014af42efd9	28
simon	0:1014af42efd9	29	/**
simon	0:1014af42efd9	30	* @ingroup groupStats
simon	0:1014af42efd9	31	*/
simon	0:1014af42efd9	32
simon	0:1014af42efd9	33	/**
simon	0:1014af42efd9	34	* @addtogroup STD
simon	0:1014af42efd9	35	* @{
simon	0:1014af42efd9	36	*/
simon	0:1014af42efd9	37
simon	0:1014af42efd9	38	/**
simon	0:1014af42efd9	39	* @brief Standard deviation of the elements of a Q15 vector.
simon	0:1014af42efd9	40	* @param[in] *pSrc points to the input vector
simon	0:1014af42efd9	41	* @param[in] blockSize length of the input vector
simon	0:1014af42efd9	42	* @param[out] *pResult standard deviation value returned here
simon	0:1014af42efd9	43	* @return none.
simon	0:1014af42efd9	44	*
simon	0:1014af42efd9	45	* @details
simon	0:1014af42efd9	46	* <b>Scaling and Overflow Behavior:</b>
simon	0:1014af42efd9	47	*
simon	0:1014af42efd9	48	* \par
simon	0:1014af42efd9	49	* The function is implemented using a 64-bit internal accumulator.
simon	0:1014af42efd9	50	* The input is represented in 1.15 format.
simon	0:1014af42efd9	51	* Intermediate multiplication yields a 2.30 format, and this
simon	0:1014af42efd9	52	* result is added without saturation to a 64-bit accumulator in 34.30 format.
simon	0:1014af42efd9	53	* With 33 guard bits in the accumulator, there is no risk of overflow, and the
simon	0:1014af42efd9	54	* full precision of the intermediate multiplication is preserved.
simon	0:1014af42efd9	55	* Finally, the 34.30 result is truncated to 34.15 format by discarding the lower
simon	0:1014af42efd9	56	* 15 bits, and then saturated to yield a result in 1.15 format.
simon	0:1014af42efd9	57	*/
simon	0:1014af42efd9	58
simon	0:1014af42efd9	59	void arm_std_q15(
simon	0:1014af42efd9	60	q15_t * pSrc,
simon	0:1014af42efd9	61	uint32_t blockSize,
simon	0:1014af42efd9	62	q15_t * pResult)
simon	0:1014af42efd9	63	{
simon	0:1014af42efd9	64	q63_t sum = 0; /* Accumulator */
simon	0:1014af42efd9	65	q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */
simon	0:1014af42efd9	66	q15_t mean; /* mean */
simon	0:1014af42efd9	67	q31_t in; /* input value */
simon	0:1014af42efd9	68	q15_t in1; /* input value */
simon	0:1014af42efd9	69	uint32_t blkCnt; /* loop counter */
simon	0:1014af42efd9	70	q15_t t; /* Temporary variable */
simon	0:1014af42efd9	71	q15_t pIn; / Temporary pointer */
simon	0:1014af42efd9	72
simon	0:1014af42efd9	73	pIn = pSrc;
simon	0:1014af42efd9	74
simon	0:1014af42efd9	75	/loop Unrolling /
simon	0:1014af42efd9	76	blkCnt = blockSize >> 2u;
simon	0:1014af42efd9	77
simon	0:1014af42efd9	78	/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
simon	0:1014af42efd9	79	** a second loop below computes the remaining 1 to 3 samples. */
simon	0:1014af42efd9	80	while(blkCnt > 0u)
simon	0:1014af42efd9	81	{
simon	0:1014af42efd9	82	/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
simon	0:1014af42efd9	83	/* Compute Sum of squares of the input samples
simon	0:1014af42efd9	84	* and then store the result in a temporary variable, sum. */
simon	0:1014af42efd9	85	in = *__SIMD32(pSrc)++;
simon	0:1014af42efd9	86	sum = __SMLALD(in, in, sum);
simon	0:1014af42efd9	87	in = *__SIMD32(pSrc)++;
simon	0:1014af42efd9	88	sum = __SMLALD(in, in, sum);
simon	0:1014af42efd9	89
simon	0:1014af42efd9	90	/* Decrement the loop counter */
simon	0:1014af42efd9	91	blkCnt--;
simon	0:1014af42efd9	92	}
simon	0:1014af42efd9	93
simon	0:1014af42efd9	94	/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
simon	0:1014af42efd9	95	** No loop unrolling is used. */
simon	0:1014af42efd9	96	blkCnt = blockSize % 0x4u;
simon	0:1014af42efd9	97
simon	0:1014af42efd9	98	while(blkCnt > 0u)
simon	0:1014af42efd9	99	{
simon	0:1014af42efd9	100	/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
simon	0:1014af42efd9	101	/* Compute Sum of squares of the input samples
simon	0:1014af42efd9	102	* and then store the result in a temporary variable, sum. */
simon	0:1014af42efd9	103	in1 = *pSrc++;
simon	0:1014af42efd9	104	sum = __SMLALD(in1, in1, sum);
simon	0:1014af42efd9	105
simon	0:1014af42efd9	106	/* Decrement the loop counter */
simon	0:1014af42efd9	107	blkCnt--;
simon	0:1014af42efd9	108	}
simon	0:1014af42efd9	109
simon	0:1014af42efd9	110	/* Compute Mean of squares of the input samples
simon	0:1014af42efd9	111	* and then store the result in a temporary variable, meanOfSquares. */
simon	0:1014af42efd9	112	t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL);
simon	0:1014af42efd9	113	sum = __SSAT((sum >> 15u), 16u);
simon	0:1014af42efd9	114
simon	0:1014af42efd9	115	meanOfSquares = (q31_t) ((sum * t) >> 14u);
simon	0:1014af42efd9	116
simon	0:1014af42efd9	117	/* Reset the accumulator */
simon	0:1014af42efd9	118	sum = 0;
simon	0:1014af42efd9	119
simon	0:1014af42efd9	120	/loop Unrolling /
simon	0:1014af42efd9	121	blkCnt = blockSize >> 2u;
simon	0:1014af42efd9	122
simon	0:1014af42efd9	123	/* Reset the input working pointer */
simon	0:1014af42efd9	124	pSrc = pIn;
simon	0:1014af42efd9	125
simon	0:1014af42efd9	126	/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
simon	0:1014af42efd9	127	** a second loop below computes the remaining 1 to 3 samples. */
simon	0:1014af42efd9	128	while(blkCnt > 0u)
simon	0:1014af42efd9	129	{
simon	0:1014af42efd9	130	/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
simon	0:1014af42efd9	131	/* Compute sum of all input values and then store the result in a temporary variable, sum. */
simon	0:1014af42efd9	132	sum += *pSrc++;
simon	0:1014af42efd9	133	sum += *pSrc++;
simon	0:1014af42efd9	134	sum += *pSrc++;
simon	0:1014af42efd9	135	sum += *pSrc++;
simon	0:1014af42efd9	136
simon	0:1014af42efd9	137	/* Decrement the loop counter */
simon	0:1014af42efd9	138	blkCnt--;
simon	0:1014af42efd9	139	}
simon	0:1014af42efd9	140
simon	0:1014af42efd9	141	/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
simon	0:1014af42efd9	142	** No loop unrolling is used. */
simon	0:1014af42efd9	143	blkCnt = blockSize % 0x4u;
simon	0:1014af42efd9	144
simon	0:1014af42efd9	145	while(blkCnt > 0u)
simon	0:1014af42efd9	146	{
simon	0:1014af42efd9	147	/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
simon	0:1014af42efd9	148	/* Compute sum of all input values and then store the result in a temporary variable, sum. */
simon	0:1014af42efd9	149	sum += *pSrc++;
simon	0:1014af42efd9	150
simon	0:1014af42efd9	151	/* Decrement the loop counter */
simon	0:1014af42efd9	152	blkCnt--;
simon	0:1014af42efd9	153	}
simon	0:1014af42efd9	154	/* Compute mean of all input values */
simon	0:1014af42efd9	155	t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL);
simon	0:1014af42efd9	156	mean = (q15_t) __SSAT(sum, 16u);
simon	0:1014af42efd9	157
simon	0:1014af42efd9	158	/* Compute square of mean */
simon	0:1014af42efd9	159	squareOfMean = ((q31_t) mean * mean) >> 15;
simon	0:1014af42efd9	160	squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
simon	0:1014af42efd9	161
simon	0:1014af42efd9	162	/* mean of the squares minus the square of the mean. */
simon	0:1014af42efd9	163	in1 = (q15_t) (meanOfSquares - squareOfMean);
simon	0:1014af42efd9	164
simon	0:1014af42efd9	165	/* Compute standard deviation and store the result to the destination */
simon	0:1014af42efd9	166	arm_sqrt_q15(in1, pResult);
simon	0:1014af42efd9	167	}
simon	0:1014af42efd9	168
simon	0:1014af42efd9	169	/**
simon	0:1014af42efd9	170	* @} end of STD group
simon	0:1014af42efd9	171	*/

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Type:	Library
Created:	10 Mar 2011
Imports:	907
Forks:	1
Commits:	3
Dependents:	5
Dependencies:	0
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src/Cortex-M4-M3/StatisticsFunctions/arm_std_q15.c@0:1014af42efd9, 2011-03-10 (annotated)

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