arm_fir_fast_q31.c
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r41 | /* ---------------------------------------------------------------------- | ||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 15. July 2011 | ||||
* $Revision: V1.0.10 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_fir_fast_q31.c | ||||
* | ||||
* Description: Processing function for the Q31 Fast FIR filter. | ||||
* | ||||
* 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. | ||||
* | ||||
* Version 0.0.9 2010/08/27 | ||||
* Initial version | ||||
* -------------------------------------------------------------------- */ | ||||
#include "arm_math.h" | ||||
/** | ||||
* @ingroup groupFilters | ||||
*/ | ||||
/** | ||||
* @addtogroup FIR | ||||
* @{ | ||||
*/ | ||||
/** | ||||
* @param[in] *S points to an instance of the Q31 structure. | ||||
* @param[in] *pSrc points to the block of input data. | ||||
* @param[out] *pDst points to the block output data. | ||||
* @param[in] blockSize number of samples to process per call. | ||||
* @return none. | ||||
* | ||||
* <b>Scaling and Overflow Behavior:</b> | ||||
* | ||||
* \par | ||||
* This function is optimized for speed at the expense of fixed-point precision and overflow protection. | ||||
* The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format. | ||||
* These intermediate results are added to a 2.30 accumulator. | ||||
* Finally, the accumulator is saturated and converted to a 1.31 result. | ||||
* The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result. | ||||
* In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits. | ||||
* | ||||
* \par | ||||
* Refer to the function <code>arm_fir_q31()</code> for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision. Both the slow and the fast versions use the same instance structure. | ||||
* Use the function <code>arm_fir_init_q31()</code> to initialize the filter structure. | ||||
*/ | ||||
void arm_fir_fast_q31( | ||||
const arm_fir_instance_q31 * S, | ||||
q31_t * pSrc, | ||||
q31_t * pDst, | ||||
uint32_t blockSize) | ||||
{ | ||||
q31_t *pState = S->pState; /* State pointer */ | ||||
q31_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | ||||
q31_t *pStateCurnt; /* Points to the current sample of the state */ | ||||
q31_t x0, x1, x2, x3; /* Temporary variables to hold state */ | ||||
q31_t c0; /* Temporary variable to hold coefficient value */ | ||||
q31_t *px; /* Temporary pointer for state */ | ||||
q31_t *pb; /* Temporary pointer for coefficient buffer */ | ||||
q63_t acc0, acc1, acc2, acc3; /* Accumulators */ | ||||
uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ | ||||
uint32_t i, 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 */ | ||||
*pStateCurnt++ = *pSrc++; | ||||
*pStateCurnt++ = *pSrc++; | ||||
*pStateCurnt++ = *pSrc++; | ||||
*pStateCurnt++ = *pSrc++; | ||||
/* Set all accumulators to zero */ | ||||
acc0 = 0; | ||||
acc1 = 0; | ||||
acc2 = 0; | ||||
acc3 = 0; | ||||
/* Initialize state pointer */ | ||||
px = pState; | ||||
/* Initialize coefficient pointer */ | ||||
pb = pCoeffs; | ||||
/* Read the first three samples from the state buffer: | ||||
* x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */ | ||||
x0 = *(px++); | ||||
x1 = *(px++); | ||||
x2 = *(px++); | ||||
/* Loop unrolling. Process 4 taps at a time. */ | ||||
tapCnt = numTaps >> 2; | ||||
i = tapCnt; | ||||
while(i > 0u) | ||||
{ | ||||
/* Read the b[numTaps] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-3] sample */ | ||||
x3 = *(px++); | ||||
/* acc0 += b[numTaps] * x[n-numTaps] */ | ||||
acc0 = (q31_t) ((((q63_t) x0 * c0) + (acc0 << 32)) >> 32); | ||||
/* acc1 += b[numTaps] * x[n-numTaps-1] */ | ||||
acc1 = (q31_t) ((((q63_t) x1 * c0) + (acc1 << 32)) >> 32); | ||||
/* acc2 += b[numTaps] * x[n-numTaps-2] */ | ||||
acc2 = (q31_t) ((((q63_t) x2 * c0) + (acc2 << 32)) >> 32); | ||||
/* acc3 += b[numTaps] * x[n-numTaps-3] */ | ||||
acc3 = (q31_t) ((((q63_t) x3 * c0) + (acc3 << 32)) >> 32); | ||||
/* Read the b[numTaps-1] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-4] sample */ | ||||
x0 = *(px++); | ||||
/* Perform the multiply-accumulates */ | ||||
acc0 = (q31_t) ((((q63_t) x1 * c0) + (acc0 << 32)) >> 32); | ||||
acc1 = (q31_t) ((((q63_t) x2 * c0) + (acc1 << 32)) >> 32); | ||||
acc2 = (q31_t) ((((q63_t) x3 * c0) + (acc2 << 32)) >> 32); | ||||
acc3 = (q31_t) ((((q63_t) x0 * c0) + (acc3 << 32)) >> 32); | ||||
/* Read the b[numTaps-2] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-5] sample */ | ||||
x1 = *(px++); | ||||
/* Perform the multiply-accumulates */ | ||||
acc0 = (q31_t) ((((q63_t) x2 * c0) + (acc0 << 32)) >> 32); | ||||
acc1 = (q31_t) ((((q63_t) x3 * c0) + (acc1 << 32)) >> 32); | ||||
acc2 = (q31_t) ((((q63_t) x0 * c0) + (acc2 << 32)) >> 32); | ||||
acc3 = (q31_t) ((((q63_t) x1 * c0) + (acc3 << 32)) >> 32); | ||||
/* Read the b[numTaps-3] coefficients */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-6] sample */ | ||||
x2 = *(px++); | ||||
/* Perform the multiply-accumulates */ | ||||
acc0 = (q31_t) ((((q63_t) x3 * c0) + (acc0 << 32)) >> 32); | ||||
acc1 = (q31_t) ((((q63_t) x0 * c0) + (acc1 << 32)) >> 32); | ||||
acc2 = (q31_t) ((((q63_t) x1 * c0) + (acc2 << 32)) >> 32); | ||||
acc3 = (q31_t) ((((q63_t) x2 * c0) + (acc3 << 32)) >> 32); | ||||
i--; | ||||
} | ||||
/* If the filter length is not a multiple of 4, compute the remaining filter taps */ | ||||
i = numTaps - (tapCnt * 4u); | ||||
while(i > 0u) | ||||
{ | ||||
/* Read coefficients */ | ||||
c0 = *(pb++); | ||||
/* Fetch 1 state variable */ | ||||
x3 = *(px++); | ||||
/* Perform the multiply-accumulates */ | ||||
acc0 = (q31_t) ((((q63_t) x0 * c0) + (acc0 << 32)) >> 32); | ||||
acc1 = (q31_t) ((((q63_t) x1 * c0) + (acc1 << 32)) >> 32); | ||||
acc2 = (q31_t) ((((q63_t) x2 * c0) + (acc2 << 32)) >> 32); | ||||
acc3 = (q31_t) ((((q63_t) x3 * c0) + (acc3 << 32)) >> 32); | ||||
/* Reuse the present sample states for next sample */ | ||||
x0 = x1; | ||||
x1 = x2; | ||||
x2 = x3; | ||||
/* Decrement the loop counter */ | ||||
i--; | ||||
} | ||||
/* Advance the state pointer by 4 to process the next group of 4 samples */ | ||||
pState = pState + 4; | ||||
/* The results in the 4 accumulators are in 2.30 format. Convert to 1.31 | ||||
** Then store the 4 outputs in the destination buffer. */ | ||||
*pDst++ = (q31_t) (acc0 << 1); | ||||
*pDst++ = (q31_t) (acc1 << 1); | ||||
*pDst++ = (q31_t) (acc2 << 1); | ||||
*pDst++ = (q31_t) (acc3 << 1); | ||||
/* Decrement the samples 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 % 4u; | ||||
while(blkCnt > 0u) | ||||
{ | ||||
/* Copy one sample at a time into state buffer */ | ||||
*pStateCurnt++ = *pSrc++; | ||||
/* Set the accumulator to zero */ | ||||
acc0 = 0; | ||||
/* Initialize state pointer */ | ||||
px = pState; | ||||
/* Initialize Coefficient pointer */ | ||||
pb = (pCoeffs); | ||||
i = numTaps; | ||||
/* Perform the multiply-accumulates */ | ||||
do | ||||
{ | ||||
acc0 = (q31_t) ((((q63_t) * (px++) * (*(pb++))) + (acc0 << 32)) >> 32); | ||||
i--; | ||||
} while(i > 0u); | ||||
/* The result is in 2.30 format. Convert to 1.31 | ||||
** Then store the output in the destination buffer. */ | ||||
*pDst++ = (q31_t) (acc0 << 1); | ||||
/* Advance state pointer by 1 for the next sample */ | ||||
pState = pState + 1; | ||||
/* Decrement the samples 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; | ||||
tapCnt = (numTaps - 1u) >> 2u; | ||||
/* copy data */ | ||||
while(tapCnt > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pState++; | ||||
*pStateCurnt++ = *pState++; | ||||
*pStateCurnt++ = *pState++; | ||||
*pStateCurnt++ = *pState++; | ||||
/* Decrement the loop counter */ | ||||
tapCnt--; | ||||
} | ||||
/* Calculate remaining number of copies */ | ||||
tapCnt = (numTaps - 1u) % 0x4u; | ||||
/* Copy the remaining q31_t data */ | ||||
while(tapCnt > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pState++; | ||||
/* Decrement the loop counter */ | ||||
tapCnt--; | ||||
} | ||||
} | ||||
/** | ||||
* @} end of FIR group | ||||
*/ | ||||