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arm_fir_fast_q31.c
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/ lib / src / stm32f4 / CPU / CMSIS / DSP_Lib / Source / FilteringFunctions / arm_fir_fast_q31.c
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/* ----------------------------------------------------------------------
* 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
*/