arm_fir_decimate_fast_q15.c
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r71 | /* ---------------------------------------------------------------------- | |||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 15. July 2011 | ||||
* $Revision: V1.0.10 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_fir_decimate_fast_q15.c | ||||
* | ||||
* Description: Fast Q15 FIR Decimator. | ||||
* | ||||
* Target Processor: Cortex-M4/Cortex-M3 | ||||
* | ||||
* Version 1.0.10 2011/7/15 | ||||
* Big Endian support added and Merged M0 and M3/M4 Source code. | ||||
* | ||||
* Version 1.0.3 2010/11/29 | ||||
* Re-organized the CMSIS folders and updated documentation. | ||||
* | ||||
* Version 1.0.2 2010/11/11 | ||||
* Documentation updated. | ||||
* | ||||
* Version 1.0.1 2010/10/05 | ||||
* Production release and review comments incorporated. | ||||
* | ||||
* Version 1.0.0 2010/09/20 | ||||
* Production release and review comments incorporated. | ||||
* -------------------------------------------------------------------- */ | ||||
#include "arm_math.h" | ||||
/** | ||||
* @ingroup groupFilters | ||||
*/ | ||||
/** | ||||
* @addtogroup FIR_decimate | ||||
* @{ | ||||
*/ | ||||
/** | ||||
* @brief Processing function for the Q15 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4. | ||||
* @param[in] *S points to an instance of the Q15 FIR decimator structure. | ||||
* @param[in] *pSrc points to the block of input data. | ||||
* @param[out] *pDst points to the block of output data | ||||
* @param[in] blockSize number of input samples to process per call. | ||||
* @return none | ||||
* | ||||
* <b>Scaling and Overflow Behavior:</b> | ||||
* \par | ||||
* This fast version uses a 32-bit accumulator with 2.30 format. | ||||
* The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. | ||||
* Thus, if the accumulator result overflows it wraps around and distorts the result. | ||||
* 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). | ||||
* The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result. | ||||
* | ||||
* \par | ||||
* 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. | ||||
* Both the slow and the fast versions use the same instance structure. | ||||
* Use the function <code>arm_fir_decimate_init_q15()</code> to initialize the filter structure. | ||||
*/ | ||||
void arm_fir_decimate_fast_q15( | ||||
const arm_fir_decimate_instance_q15 * S, | ||||
q15_t * pSrc, | ||||
q15_t * pDst, | ||||
uint32_t blockSize) | ||||
{ | ||||
q15_t *pState = S->pState; /* State pointer */ | ||||
q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | ||||
q15_t *pStateCurnt; /* Points to the current sample of the state */ | ||||
q15_t *px; /* Temporary pointer for state buffer */ | ||||
q15_t *pb; /* Temporary pointer coefficient buffer */ | ||||
q31_t x0, c0; /* Temporary variables to hold state and coefficient values */ | ||||
q31_t sum0; /* Accumulators */ | ||||
uint32_t numTaps = S->numTaps; /* Number of taps */ | ||||
uint32_t i, blkCnt, tapCnt, outBlockSize = blockSize / S->M; /* Loop counters */ | ||||
/* S->pState buffer contains previous frame (numTaps - 1) samples */ | ||||
/* pStateCurnt points to the location where the new input data should be written */ | ||||
pStateCurnt = S->pState + (numTaps - 1u); | ||||
/* Total number of output samples to be computed */ | ||||
blkCnt = outBlockSize; | ||||
while(blkCnt > 0u) | ||||
{ | ||||
/* Copy decimation factor number of new input samples into the state buffer */ | ||||
i = S->M; | ||||
do | ||||
{ | ||||
*pStateCurnt++ = *pSrc++; | ||||
} while(--i); | ||||
/*Set sum to zero */ | ||||
sum0 = 0; | ||||
/* Initialize state pointer */ | ||||
px = pState; | ||||
/* Initialize coeff pointer */ | ||||
pb = pCoeffs; | ||||
/* Loop unrolling. Process 4 taps at a time. */ | ||||
tapCnt = numTaps >> 2; | ||||
/* Loop over the number of taps. Unroll by a factor of 4. | ||||
** Repeat until we've computed numTaps-4 coefficients. */ | ||||
while(tapCnt > 0u) | ||||
{ | ||||
/* Read the Read b[numTaps-1] and b[numTaps-2] coefficients */ | ||||
c0 = *__SIMD32(pb)++; | ||||
/* Read x[n-numTaps-1] and x[n-numTaps-2]sample */ | ||||
x0 = *__SIMD32(px)++; | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = __SMLAD(x0, c0, sum0); | ||||
/* Read the b[numTaps-3] and b[numTaps-4] coefficient */ | ||||
c0 = *__SIMD32(pb)++; | ||||
/* Read x[n-numTaps-2] and x[n-numTaps-3] sample */ | ||||
x0 = *__SIMD32(px)++; | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = __SMLAD(x0, c0, sum0); | ||||
/* Decrement the loop counter */ | ||||
tapCnt--; | ||||
} | ||||
/* If the filter length is not a multiple of 4, compute the remaining filter taps */ | ||||
tapCnt = numTaps % 0x4u; | ||||
while(tapCnt > 0u) | ||||
{ | ||||
/* Read coefficients */ | ||||
c0 = *pb++; | ||||
/* Fetch 1 state variable */ | ||||
x0 = *px++; | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = __SMLAD(x0, c0, sum0); | ||||
/* Decrement the loop counter */ | ||||
tapCnt--; | ||||
} | ||||
/* Advance the state pointer by the decimation factor | ||||
* to process the next group of decimation factor number samples */ | ||||
pState = pState + S->M; | ||||
/* Store filter output , smlad returns the values in 2.14 format */ | ||||
/* so downsacle by 15 to get output in 1.15 */ | ||||
*pDst++ = (q15_t) ((sum0 >> 15)); | ||||
/* Decrement the loop counter */ | ||||
blkCnt--; | ||||
} | ||||
/* Processing is complete. | ||||
** Now copy the last numTaps - 1 samples to the satrt of the state buffer. | ||||
** This prepares the state buffer for the next function call. */ | ||||
/* Points to the start of the state buffer */ | ||||
pStateCurnt = S->pState; | ||||
i = (numTaps - 1u) >> 2u; | ||||
/* copy data */ | ||||
while(i > 0u) | ||||
{ | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; | ||||
/* Decrement the loop counter */ | ||||
i--; | ||||
} | ||||
i = (numTaps - 1u) % 0x04u; | ||||
/* copy data */ | ||||
while(i > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pState++; | ||||
/* Decrement the loop counter */ | ||||
i--; | ||||
} | ||||
} | ||||
/** | ||||
* @} end of FIR_decimate group | ||||
*/ | ||||