arm_fir_decimate_fast_q31.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_decimate_fast_q31.c | ||||
* | ||||
* Description: Fast Q31 FIR Decimator. | ||||
* | ||||
* 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. | ||||
* -------------------------------------------------------------------- */ | ||||
#include "arm_math.h" | ||||
/** | ||||
* @ingroup groupFilters | ||||
*/ | ||||
/** | ||||
* @addtogroup FIR_decimate | ||||
* @{ | ||||
*/ | ||||
/** | ||||
* @brief Processing function for the Q31 FIR decimator (fast variant). | ||||
* @param[in] *S points to an instance of the Q31 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 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 (where log2 is read as log to the base 2). | ||||
* | ||||
* \par | ||||
* Refer to the function <code>arm_fir_decimate_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_decimate_init_q31()</code> to initialize the filter structure. | ||||
*/ | ||||
void arm_fir_decimate_fast_q31( | ||||
arm_fir_decimate_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, c0; /* Temporary variables to hold state and coefficient values */ | ||||
q31_t *px; /* Temporary pointers for state buffer */ | ||||
q31_t *pb; /* Temporary pointers for coefficient buffer */ | ||||
q63_t sum0; /* Accumulator */ | ||||
uint32_t numTaps = S->numTaps; /* Number of taps */ | ||||
uint32_t i, tapCnt, blkCnt, 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 accumulator 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 b[numTaps-1] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-1] sample */ | ||||
x0 = *(px++); | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); | ||||
/* Read the b[numTaps-2] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-2] sample */ | ||||
x0 = *(px++); | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); | ||||
/* Read the b[numTaps-3] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-3] sample */ | ||||
x0 = *(px++); | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); | ||||
/* Read the b[numTaps-4] coefficient */ | ||||
c0 = *(pb++); | ||||
/* Read x[n-numTaps-4] sample */ | ||||
x0 = *(px++); | ||||
/* Perform the multiply-accumulate */ | ||||
sum0 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); | ||||
/* 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 = (q31_t) ((((q63_t) x0 * c0) + (sum0 << 32)) >> 32); | ||||
/* 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; | ||||
/* The result is in the accumulator, store in the destination buffer. */ | ||||
*pDst++ = (q31_t) (sum0 << 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; | ||||
i = (numTaps - 1u) >> 2u; | ||||
/* copy data */ | ||||
while(i > 0u) | ||||
{ | ||||
*pStateCurnt++ = *pState++; | ||||
*pStateCurnt++ = *pState++; | ||||
*pStateCurnt++ = *pState++; | ||||
*pStateCurnt++ = *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 | ||||
*/ | ||||