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src/Cortex-M4-M3/FilteringFunctions/arm_fir_decimate_fast_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_fir_decimate_fast_q15.c
simon	0:1014af42efd9	9	*
simon	0:1014af42efd9	10	* Description: Fast Q15 FIR Decimator.
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 groupFilters
simon	0:1014af42efd9	31	*/
simon	0:1014af42efd9	32
simon	0:1014af42efd9	33	/**
simon	0:1014af42efd9	34	* @addtogroup FIR_decimate
simon	0:1014af42efd9	35	* @{
simon	0:1014af42efd9	36	*/
simon	0:1014af42efd9	37
simon	0:1014af42efd9	38	/**
simon	0:1014af42efd9	39	* @brief Processing function for the Q15 FIR decimator (fast variant).
simon	0:1014af42efd9	40	* @param[in] *S points to an instance of the Q15 FIR decimator structure.
simon	0:1014af42efd9	41	* @param[in] *pSrc points to the block of input data.
simon	0:1014af42efd9	42	* @param[out] *pDst points to the block of output data
simon	0:1014af42efd9	43	* @param[in] blockSize number of input samples to process per call.
simon	0:1014af42efd9	44	* @return none
simon	0:1014af42efd9	45	*
simon	0:1014af42efd9	46	* <b>Scaling and Overflow Behavior:</b>
simon	0:1014af42efd9	47	* \par
simon	0:1014af42efd9	48	* This fast version uses a 32-bit accumulator with 2.30 format.
simon	0:1014af42efd9	49	* The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.
simon	0:1014af42efd9	50	* Thus, if the accumulator result overflows it wraps around and distorts the result.
simon	0:1014af42efd9	51	* In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (log2 is read as log to the base 2).
simon	0:1014af42efd9	52	* The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result.
simon	0:1014af42efd9	53	*
simon	0:1014af42efd9	54	* \par
simon	0:1014af42efd9	55	* Refer to the function <code>arm_fir_decimate_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion.
simon	0:1014af42efd9	56	* Both the slow and the fast versions use the same instance structure.
simon	0:1014af42efd9	57	* Use the function <code>arm_fir_decimate_init_q15()</code> to initialize the filter structure.
simon	0:1014af42efd9	58	*/
simon	0:1014af42efd9	59
simon	0:1014af42efd9	60	void arm_fir_decimate_fast_q15(
simon	0:1014af42efd9	61	const arm_fir_decimate_instance_q15 * S,
simon	0:1014af42efd9	62	q15_t * pSrc,
simon	0:1014af42efd9	63	q15_t * pDst,
simon	0:1014af42efd9	64	uint32_t blockSize)
simon	0:1014af42efd9	65	{
simon	0:1014af42efd9	66	q15_t pState = S->pState; / State pointer */
simon	0:1014af42efd9	67	q15_t pCoeffs = S->pCoeffs; / Coefficient pointer */
simon	0:1014af42efd9	68	q15_t pStateCurnt; / Points to the current sample of the state */
simon	0:1014af42efd9	69	q15_t px; / Temporary pointer for state buffer */
simon	0:1014af42efd9	70	q15_t pb; / Temporary pointer coefficient buffer */
simon	0:1014af42efd9	71	q31_t x0, c0; /* Temporary variables to hold state and coefficient values */
simon	0:1014af42efd9	72	q31_t sum0; /* Accumulators */
simon	0:1014af42efd9	73	uint32_t numTaps = S->numTaps; /* Number of taps */
simon	0:1014af42efd9	74	uint32_t i, blkCnt, tapCnt, outBlockSize = blockSize / S->M; /* Loop counters */
simon	0:1014af42efd9	75
simon	0:1014af42efd9	76
simon	0:1014af42efd9	77	/* S->pState buffer contains previous frame (numTaps - 1) samples */
simon	0:1014af42efd9	78	/* pStateCurnt points to the location where the new input data should be written */
simon	0:1014af42efd9	79	pStateCurnt = S->pState + (numTaps - 1u);
simon	0:1014af42efd9	80
simon	0:1014af42efd9	81	/* Total number of output samples to be computed */
simon	0:1014af42efd9	82	blkCnt = outBlockSize;
simon	0:1014af42efd9	83
simon	0:1014af42efd9	84	while(blkCnt > 0u)
simon	0:1014af42efd9	85	{
simon	0:1014af42efd9	86	/* Copy decimation factor number of new input samples into the state buffer */
simon	0:1014af42efd9	87	i = S->M;
simon	0:1014af42efd9	88
simon	0:1014af42efd9	89	do
simon	0:1014af42efd9	90	{
simon	0:1014af42efd9	91	pStateCurnt++ = pSrc++;
simon	0:1014af42efd9	92
simon	0:1014af42efd9	93	} while(--i);
simon	0:1014af42efd9	94
simon	0:1014af42efd9	95	/Set sum to zero /
simon	0:1014af42efd9	96	sum0 = 0;
simon	0:1014af42efd9	97
simon	0:1014af42efd9	98	/* Initialize state pointer */
simon	0:1014af42efd9	99	px = pState;
simon	0:1014af42efd9	100
simon	0:1014af42efd9	101	/* Initialize coeff pointer */
simon	0:1014af42efd9	102	pb = pCoeffs;
simon	0:1014af42efd9	103
simon	0:1014af42efd9	104	/* Loop unrolling. Process 4 taps at a time. */
simon	0:1014af42efd9	105	tapCnt = numTaps >> 2;
simon	0:1014af42efd9	106
simon	0:1014af42efd9	107	/* Loop over the number of taps. Unroll by a factor of 4.
simon	0:1014af42efd9	108	** Repeat until we've computed numTaps-4 coefficients. */
simon	0:1014af42efd9	109	while(tapCnt > 0u)
simon	0:1014af42efd9	110	{
simon	0:1014af42efd9	111	/* Read the Read b[numTaps-1] and b[numTaps-2] coefficients */
simon	0:1014af42efd9	112	c0 = *__SIMD32(pb)++;
simon	0:1014af42efd9	113
simon	0:1014af42efd9	114	/* Read x[n-numTaps-1] and x[n-numTaps-2]sample */
simon	0:1014af42efd9	115	x0 = *__SIMD32(px)++;
simon	0:1014af42efd9	116
simon	0:1014af42efd9	117	/* Perform the multiply-accumulate */
simon	0:1014af42efd9	118	sum0 = __SMLAD(x0, c0, sum0);
simon	0:1014af42efd9	119
simon	0:1014af42efd9	120	/* Read the b[numTaps-3] and b[numTaps-4] coefficient */
simon	0:1014af42efd9	121	c0 = *__SIMD32(pb)++;
simon	0:1014af42efd9	122
simon	0:1014af42efd9	123	/* Read x[n-numTaps-2] and x[n-numTaps-3] sample */
simon	0:1014af42efd9	124	x0 = *__SIMD32(px)++;
simon	0:1014af42efd9	125
simon	0:1014af42efd9	126	/* Perform the multiply-accumulate */
simon	0:1014af42efd9	127	sum0 = __SMLAD(x0, c0, sum0);
simon	0:1014af42efd9	128
simon	0:1014af42efd9	129	/* Decrement the loop counter */
simon	0:1014af42efd9	130	tapCnt--;
simon	0:1014af42efd9	131	}
simon	0:1014af42efd9	132
simon	0:1014af42efd9	133	/* If the filter length is not a multiple of 4, compute the remaining filter taps */
simon	0:1014af42efd9	134	tapCnt = numTaps % 0x4u;
simon	0:1014af42efd9	135
simon	0:1014af42efd9	136	while(tapCnt > 0u)
simon	0:1014af42efd9	137	{
simon	0:1014af42efd9	138	/* Read coefficients */
simon	0:1014af42efd9	139	c0 = *pb++;
simon	0:1014af42efd9	140
simon	0:1014af42efd9	141	/* Fetch 1 state variable */
simon	0:1014af42efd9	142	x0 = *px++;
simon	0:1014af42efd9	143
simon	0:1014af42efd9	144	/* Perform the multiply-accumulate */
simon	0:1014af42efd9	145	sum0 = __SMLAD(x0, c0, sum0);
simon	0:1014af42efd9	146
simon	0:1014af42efd9	147	/* Decrement the loop counter */
simon	0:1014af42efd9	148	tapCnt--;
simon	0:1014af42efd9	149	}
simon	0:1014af42efd9	150
simon	0:1014af42efd9	151	/* Advance the state pointer by the decimation factor
simon	0:1014af42efd9	152	* to process the next group of decimation factor number samples */
simon	0:1014af42efd9	153	pState = pState + S->M;
simon	0:1014af42efd9	154
simon	0:1014af42efd9	155	/* Store filter output , smlad returns the values in 2.14 format */
simon	0:1014af42efd9	156	/* so downsacle by 15 to get output in 1.15 */
simon	0:1014af42efd9	157	*pDst++ = (q15_t) ((sum0 >> 15));
simon	0:1014af42efd9	158
simon	0:1014af42efd9	159	/* Decrement the loop counter */
simon	0:1014af42efd9	160	blkCnt--;
simon	0:1014af42efd9	161	}
simon	0:1014af42efd9	162
simon	0:1014af42efd9	163	/* Processing is complete.
simon	0:1014af42efd9	164	** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
simon	0:1014af42efd9	165	** This prepares the state buffer for the next function call. */
simon	0:1014af42efd9	166
simon	0:1014af42efd9	167	/* Points to the start of the state buffer */
simon	0:1014af42efd9	168	pStateCurnt = S->pState;
simon	0:1014af42efd9	169
simon	0:1014af42efd9	170	i = (numTaps - 1u) >> 2u;
simon	0:1014af42efd9	171
simon	0:1014af42efd9	172	/* copy data */
simon	0:1014af42efd9	173	while(i > 0u)
simon	0:1014af42efd9	174	{
simon	0:1014af42efd9	175	__SIMD32(pStateCurnt)++ = __SIMD32(pState)++;
simon	0:1014af42efd9	176	__SIMD32(pStateCurnt)++ = __SIMD32(pState)++;
simon	0:1014af42efd9	177
simon	0:1014af42efd9	178	/* Decrement the loop counter */
simon	0:1014af42efd9	179	i--;
simon	0:1014af42efd9	180	}
simon	0:1014af42efd9	181
simon	0:1014af42efd9	182	i = (numTaps - 1u) % 0x04u;
simon	0:1014af42efd9	183
simon	0:1014af42efd9	184	/* copy data */
simon	0:1014af42efd9	185	while(i > 0u)
simon	0:1014af42efd9	186	{
simon	0:1014af42efd9	187	pStateCurnt++ = pState++;
simon	0:1014af42efd9	188
simon	0:1014af42efd9	189	/* Decrement the loop counter */
simon	0:1014af42efd9	190	i--;
simon	0:1014af42efd9	191	}
simon	0:1014af42efd9	192	}
simon	0:1014af42efd9	193
simon	0:1014af42efd9	194	/**
simon	0:1014af42efd9	195	* @} end of FIR_decimate group
simon	0:1014af42efd9	196	*/

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Type:	Library
Created:	10 Mar 2011
Imports:	907
Forks:	1
Commits:	3
Dependents:	5
Dependencies:	0
Followers:	35

src/Cortex-M4-M3/FilteringFunctions/arm_fir_decimate_fast_q15.c@0:1014af42efd9, 2011-03-10 (annotated)

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