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arm_fir_q15.c
368 lines | 11.9 KiB | text/x-c | CLexer
/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date: 15. July 2011
* $Revision: V1.0.10
*
* Project: CMSIS DSP Library
* Title: arm_fir_q15.c
*
* Description: Q15 FIR filter processing function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* 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 0.0.5 2010/04/26
* incorporated review comments and updated with latest CMSIS layer
*
* Version 0.0.3 2010/03/10
* Initial version
* -------------------------------------------------------------------- */
#include "arm_math.h"
/**
* @ingroup groupFilters
*/
/**
* @addtogroup FIR
* @{
*/
/**
* @brief Processing function for the Q15 FIR filter.
* @param[in] *S points to an instance of the Q15 FIR 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
* The function is implemented using a 64-bit internal accumulator.
* Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result.
* The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format.
* There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved.
* After all additions have been performed, the accumulator is truncated to 34.15 format by discarding low 15 bits.
* Lastly, the accumulator is saturated to yield a result in 1.15 format.
*
* \par
* Refer to the function <code>arm_fir_fast_q15()</code> for a faster but less precise implementation of this function for Cortex-M3 and Cortex-M4.
*/
void arm_fir_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 */
#ifndef ARM_MATH_CM0
/* Run the below code for Cortex-M4 and Cortex-M3 */
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 */
q63_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 state array 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 = __SMLALD(x0, c0, acc0);
/* acc1 += b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */
acc1 = __SMLALD(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 = __SMLALD(x2, c0, acc2);
/* acc3 += b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */
acc3 = __SMLALD(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 = __SMLALD(x2, c0, acc0);
/* acc1 += b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */
acc1 = __SMLALD(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 = __SMLALD(x0, c0, acc2);
/* acc3 += b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */
acc3 = __SMLALD(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 be 2 taps since the filter length is 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 = __SMLALD(x0, c0, acc0);
acc1 = __SMLALD(x1, c0, acc1);
acc2 = __SMLALD(x2, c0, acc2);
acc3 = __SMLALD(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. */
#ifndef ARM_MATH_BIG_ENDIAN
*__SIMD32(pDst)++ =
__PKHBT(__SSAT((acc0 >> 15), 16), __SSAT((acc1 >> 15), 16), 16);
*__SIMD32(pDst)++ =
__PKHBT(__SSAT((acc2 >> 15), 16), __SSAT((acc3 >> 15), 16), 16);
#else
*__SIMD32(pDst)++ =
__PKHBT(__SSAT((acc1 >> 15), 16), __SSAT((acc0 >> 15), 16), 16);
*__SIMD32(pDst)++ =
__PKHBT(__SSAT((acc3 >> 15), 16), __SSAT((acc2 >> 15), 16), 16);
#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
/* 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 = __SMLALD(*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) (__SSAT((acc0 >> 15), 16));
/* 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--;
}
#else
/* Run the below code for Cortex-M0 */
q15_t *px; /* Temporary pointer for state buffer */
q15_t *pb; /* Temporary pointer for coefficient buffer */
q63_t acc; /* Accumulator */
uint32_t numTaps = S->numTaps; /* Number of nTaps in the filter */
uint32_t tapCnt, blkCnt; /* 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)]);
/* Initialize blkCnt with blockSize */
blkCnt = blockSize;
while(blkCnt > 0u)
{
/* Copy one sample at a time into state buffer */
*pStateCurnt++ = *pSrc++;
/* Set the accumulator to zero */
acc = 0;
/* Initialize state pointer */
px = pState;
/* Initialize Coefficient pointer */
pb = pCoeffs;
tapCnt = numTaps;
/* Perform the multiply-accumulates */
do
{
/* acc = 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] */
acc += (q31_t) * px++ * *pb++;
tapCnt--;
} while(tapCnt > 0u);
/* The result is in 2.30 format. Convert to 1.15
** Then store the output in the destination buffer. */
*pDst++ = (q15_t) __SSAT((acc >> 15u), 16);
/* 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;
/* Copy numTaps number of values */
tapCnt = (numTaps - 1u);
/* copy data */
while(tapCnt > 0u)
{
*pStateCurnt++ = *pState++;
/* Decrement the loop counter */
tapCnt--;
}
#endif /* #ifndef ARM_MATH_CM0 */
}
/**
* @} end of FIR group
*/