arm_fir_fast_q15.c
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r16 | /* ---------------------------------------------------------------------- | ||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 29. November 2010 | ||||
* $Revision: V1.0.3 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_fir_fast_q15.c | ||||
* | ||||
* Description: Q15 Fast FIR filter processing function. | ||||
* | ||||
* Target Processor: Cortex-M4/Cortex-M3 | ||||
* | ||||
* 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. | ||||
* | ||||
* Version 0.0.9 2010/08/16 | ||||
* Initial version | ||||
* | ||||
* -------------------------------------------------------------------- */ | ||||
#include "arm_math.h" | ||||
/** | ||||
* @ingroup groupFilters | ||||
*/ | ||||
/** | ||||
* @addtogroup FIR | ||||
* @{ | ||||
*/ | ||||
/** | ||||
* @param[in] *S points to an instance of the Q15 FIR filter 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 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. | ||||
* 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_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_init_q15()</code> to initialize the filter structure. | ||||
*/ | ||||
void arm_fir_fast_q15( | ||||
const arm_fir_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 *px1; /* Temporary q15 pointer for state buffer */ | ||||
q31_t *pb; /* Temporary pointer for coefficient buffer */ | ||||
q31_t *px2; /* Temporary q31 pointer for SIMD state buffer accesses */ | ||||
q31_t x0, x1, x2, x3, c0; /* Temporary variables to hold SIMD state and coefficient values */ | ||||
q31_t acc0, acc1, acc2, acc3; /* Accumulators */ | ||||
uint32_t numTaps = S->numTaps; /* Number of taps in the filter */ | ||||
uint32_t tapCnt, blkCnt; /* Loop counters */ | ||||
/* S->pState points to buffer which contains previous frame (numTaps - 1) samples */ | ||||
/* pStateCurnt points to the location where the new input data should be written */ | ||||
pStateCurnt = &(S->pState[(numTaps - 1u)]); | ||||
/* Apply loop unrolling and compute 4 output values simultaneously. | ||||
* The variables acc0 ... acc3 hold output values that are being computed: | ||||
* | ||||
* acc0 = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] | ||||
* acc1 = b[numTaps-1] * x[n-numTaps] + b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1] | ||||
* acc2 = b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] + b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2] | ||||
* acc3 = b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps] +...+ b[0] * x[3] | ||||
*/ | ||||
blkCnt = blockSize >> 2; | ||||
/* First part of the processing with loop unrolling. Compute 4 outputs at a time. | ||||
** a second loop below computes the remaining 1 to 3 samples. */ | ||||
while(blkCnt > 0u) | ||||
{ | ||||
/* Copy four new input samples into the state buffer. | ||||
** Use 32-bit SIMD to move the 16-bit data. Only requires two copies. */ | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; | ||||
/* Set all accumulators to zero */ | ||||
acc0 = 0; | ||||
acc1 = 0; | ||||
acc2 = 0; | ||||
acc3 = 0; | ||||
/* Initialize state pointer of type q15 */ | ||||
px1 = pState; | ||||
/* Initialize coeff pointer of type q31 */ | ||||
pb = (q31_t *) (pCoeffs); | ||||
/* Read the first two samples from the state buffer: x[n-N], x[n-N-1] */ | ||||
x0 = *(q31_t *) (px1++); | ||||
/* Read the third and forth samples from the state buffer: x[n-N-1], x[n-N-2] */ | ||||
x1 = *(q31_t *) (px1++); | ||||
/* Loop over the number of taps. Unroll by a factor of 4. | ||||
** Repeat until we've computed numTaps-4 coefficients. */ | ||||
tapCnt = numTaps >> 2; | ||||
do | ||||
{ | ||||
/* Read the first two coefficients using SIMD: b[N] and b[N-1] coefficients */ | ||||
c0 = *(pb++); | ||||
/* acc0 += b[N] * x[n-N] + b[N-1] * x[n-N-1] */ | ||||
acc0 = __SMLAD(x0, c0, acc0); | ||||
/* acc1 += b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */ | ||||
acc1 = __SMLAD(x1, c0, acc1); | ||||
/* Read state x[n-N-2], x[n-N-3] */ | ||||
x2 = *(q31_t *) (px1++); | ||||
/* Read state x[n-N-3], x[n-N-4] */ | ||||
x3 = *(q31_t *) (px1++); | ||||
/* acc2 += b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */ | ||||
acc2 = __SMLAD(x2, c0, acc2); | ||||
/* acc3 += b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */ | ||||
acc3 = __SMLAD(x3, c0, acc3); | ||||
/* Read coefficients b[N-2], b[N-3] */ | ||||
c0 = *(pb++); | ||||
/* acc0 += b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */ | ||||
acc0 = __SMLAD(x2, c0, acc0); | ||||
/* acc1 += b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */ | ||||
acc1 = __SMLAD(x3, c0, acc1); | ||||
/* Read state x[n-N-4], x[n-N-5] */ | ||||
x0 = *(q31_t *) (px1++); | ||||
/* Read state x[n-N-5], x[n-N-6] */ | ||||
x1 = *(q31_t *) (px1++); | ||||
/* acc2 += b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */ | ||||
acc2 = __SMLAD(x0, c0, acc2); | ||||
/* acc3 += b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */ | ||||
acc3 = __SMLAD(x1, c0, acc3); | ||||
tapCnt--; | ||||
} | ||||
while(tapCnt > 0u); | ||||
/* If the filter length is not a multiple of 4, compute the remaining filter taps. | ||||
** This is always 2 taps since the filter length is always even. */ | ||||
if((numTaps & 0x3u) != 0u) | ||||
{ | ||||
/* Read 2 coefficients */ | ||||
c0 = *(pb++); | ||||
/* Fetch 4 state variables */ | ||||
x2 = *(q31_t *) (px1++); | ||||
x3 = *(q31_t *) (px1++); | ||||
/* Perform the multiply-accumulates */ | ||||
acc0 = __SMLAD(x0, c0, acc0); | ||||
acc1 = __SMLAD(x1, c0, acc1); | ||||
acc2 = __SMLAD(x2, c0, acc2); | ||||
acc3 = __SMLAD(x3, c0, acc3); | ||||
} | ||||
/* The results in the 4 accumulators are in 2.30 format. Convert to 1.15 with saturation. | ||||
** Then store the 4 outputs in the destination buffer. */ | ||||
*__SIMD32(pDst)++ = __PKHBT((acc0 >> 15), (acc1 >> 15), 16u); | ||||
*__SIMD32(pDst)++ = __PKHBT((acc2 >> 15), (acc3 >> 15), 16u); | ||||
/* Advance the state pointer by 4 to process the next group of 4 samples */ | ||||
pState = pState + 4; | ||||
/* Decrement the loop counter */ | ||||
blkCnt--; | ||||
} | ||||
/* If the blockSize is not a multiple of 4, compute any remaining output samples here. | ||||
** No loop unrolling is used. */ | ||||
blkCnt = blockSize % 0x4u; | ||||
while(blkCnt > 0u) | ||||
{ | ||||
/* Copy two samples into state buffer */ | ||||
*pStateCurnt++ = *pSrc++; | ||||
/* Set the accumulator to zero */ | ||||
acc0 = 0; | ||||
/* Use SIMD to hold states and coefficients */ | ||||
px2 = (q31_t *) pState; | ||||
pb = (q31_t *) (pCoeffs); | ||||
tapCnt = numTaps >> 1; | ||||
do | ||||
{ | ||||
acc0 = __SMLAD(*px2++, *(pb++), acc0); | ||||
tapCnt--; | ||||
} | ||||
while(tapCnt > 0u); | ||||
/* The result is in 2.30 format. Convert to 1.15 with saturation. | ||||
** Then store the output in the destination buffer. */ | ||||
*pDst++ = (q15_t) ((acc0 >> 15)); | ||||
/* Advance state pointer by 1 for the next sample */ | ||||
pState = pState + 1; | ||||
/* 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; | ||||
/* Calculation of count for copying integer writes */ | ||||
tapCnt = (numTaps - 1u) >> 2; | ||||
while(tapCnt > 0u) | ||||
{ | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; | ||||
*__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; | ||||
tapCnt--; | ||||
} | ||||
/* Calculation of count for remaining q15_t data */ | ||||
tapCnt = (numTaps - 1u) % 0x4u; | ||||
/* copy remaining data */ | ||||
while(tapCnt > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pState++; | ||||
/* Decrement the loop counter */ | ||||
tapCnt--; | ||||
} | ||||
} | ||||
/** | ||||
* @} end of FIR group | ||||
*/ | ||||