arm_biquad_cascade_df1_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_biquad_cascade_df1_q15.c | ||||
* | ||||
* Description: Processing function for the | ||||
* Q15 Biquad cascade DirectFormI(DF1) filter. | ||||
* | ||||
* 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 0.0.5 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 BiquadCascadeDF1 | ||||
* @{ | ||||
*/ | ||||
/** | ||||
* @brief Processing function for the Q15 Biquad cascade filter. | ||||
* @param[in] *S points to an instance of the Q15 Biquad cascade structure. | ||||
* @param[in] *pSrc points to the block of input data. | ||||
* @param[out] *pDst points to the location where the output result is written. | ||||
* @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. | ||||
* The accumulator is then shifted by <code>postShift</code> bits to truncate the result to 1.15 format by discarding the low 16 bits. | ||||
* Finally, the result is saturated to 1.15 format. | ||||
* | ||||
* \par | ||||
* Refer to the function <code>arm_biquad_cascade_df1_fast_q15()</code> for a faster but less precise implementation of this filter. | ||||
*/ | ||||
void arm_biquad_cascade_df1_q15( | ||||
const arm_biquad_casd_df1_inst_q15 * S, | ||||
q15_t * pSrc, | ||||
q15_t * pDst, | ||||
uint32_t blockSize) | ||||
{ | ||||
q15_t *pIn = pSrc; /* Source pointer */ | ||||
q15_t *pOut = pDst; /* Destination pointer */ | ||||
q31_t in; /* Temporary variable to hold input value */ | ||||
q31_t out; /* Temporary variable to hold output value */ | ||||
q15_t b0; /* Temporary variable to hold bo value */ | ||||
q31_t b1, a1; /* Filter coefficients */ | ||||
q31_t state_in, state_out; /* Filter state variables */ | ||||
q63_t acc; /* Accumulator */ | ||||
int32_t shift = (15 - (int32_t) S->postShift); /* Post shift */ | ||||
q15_t *pState = S->pState; /* State pointer */ | ||||
q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ | ||||
q31_t *pState_q31; /* 32-bit state pointer for SIMD implementation */ | ||||
uint32_t sample, stage = (uint32_t) S->numStages; /* Stage loop counter */ | ||||
do | ||||
{ | ||||
/* Initialize state pointer of type q31 */ | ||||
pState_q31 = (q31_t *) (pState); | ||||
/* Read the b0 and 0 coefficients using SIMD */ | ||||
b0 = *__SIMD32(pCoeffs)++; | ||||
/* Read the b1 and b2 coefficients using SIMD */ | ||||
b1 = *__SIMD32(pCoeffs)++; | ||||
/* Read the a1 and a2 coefficients using SIMD */ | ||||
a1 = *__SIMD32(pCoeffs)++; | ||||
/* Read the input state values from the state buffer: x[n-1], x[n-2] */ | ||||
state_in = (q31_t) (*pState_q31++); | ||||
/* Read the output state values from the state buffer: y[n-1], y[n-2] */ | ||||
state_out = (q31_t) (*pState_q31); | ||||
/* Apply loop unrolling and compute 2 output values simultaneously. */ | ||||
/* The variable acc hold output values that are being computed: | ||||
* | ||||
* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] | ||||
* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] | ||||
*/ | ||||
sample = blockSize >> 1u; | ||||
/* First part of the processing with loop unrolling. Compute 2 outputs at a time. | ||||
** a second loop below computes the remaining 1 sample. */ | ||||
while(sample > 0u) | ||||
{ | ||||
/* Read the input */ | ||||
in = *__SIMD32(pIn)++; | ||||
/* out = b0 * x[n] + 0 * 0 */ | ||||
out = (q31_t) b0 * ((q15_t) in); | ||||
/* acc += b1 * x[n-1] + b2 * x[n-2] + out */ | ||||
acc = __SMLALD(b1, state_in, out); | ||||
/* acc += a1 * y[n-1] + a2 * y[n-2] */ | ||||
acc = __SMLALD(a1, state_out, acc); | ||||
/* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */ | ||||
out = __SSAT((acc >> shift), 16); | ||||
/* Every time after the output is computed state should be updated. */ | ||||
/* The states should be updated as: */ | ||||
/* Xn2 = Xn1 */ | ||||
/* Xn1 = Xn */ | ||||
/* Yn2 = Yn1 */ | ||||
/* Yn1 = acc */ | ||||
/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */ | ||||
/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */ | ||||
state_in = __PKHBT(in, state_in, 16); | ||||
state_out = __PKHBT(out, state_out, 16); | ||||
/* out = b0 * x[n] + 0 * 0 */ | ||||
out = (q31_t) b0 * ((q15_t) (in >> 16)); | ||||
/* acc += b1 * x[n-1] + b2 * x[n-2] + out */ | ||||
acc = __SMLALD(b1, state_in, out); | ||||
/* acc += a1 * y[n-1] + a2 * y[n-2] */ | ||||
acc = __SMLALD(a1, state_out, acc); | ||||
/* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */ | ||||
out = __SSAT((acc >> shift), 16); | ||||
/* Store the output in the destination buffer. */ | ||||
*__SIMD32(pOut)++ = __PKHBT(state_out, out, 16); | ||||
/* Every time after the output is computed state should be updated. */ | ||||
/* The states should be updated as: */ | ||||
/* Xn2 = Xn1 */ | ||||
/* Xn1 = Xn */ | ||||
/* Yn2 = Yn1 */ | ||||
/* Yn1 = acc */ | ||||
/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */ | ||||
/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */ | ||||
state_in = __PKHBT(in >> 16, state_in, 16); | ||||
state_out = __PKHBT(out, state_out, 16); | ||||
/* Decrement the loop counter */ | ||||
sample--; | ||||
} | ||||
/* If the blockSize is not a multiple of 2, compute any remaining output samples here. | ||||
** No loop unrolling is used. */ | ||||
if((blockSize & 0x1u) != 0u) | ||||
{ | ||||
/* Read the input */ | ||||
in = *pIn++; | ||||
/* out = b0 * x[n] + 0 * 0 */ | ||||
out = (q31_t) in *b0; | ||||
/* acc = b1 * x[n-1] + b2 * x[n-2] + out */ | ||||
acc = __SMLALD(b1, state_in, out); | ||||
/* acc += a1 * y[n-1] + a2 * y[n-2] */ | ||||
acc = __SMLALD(a1, state_out, acc); | ||||
/* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */ | ||||
out = __SSAT((acc >> shift), 16); | ||||
/* Store the output in the destination buffer. */ | ||||
*pOut++ = (q15_t) out; | ||||
/* Every time after the output is computed state should be updated. */ | ||||
/* The states should be updated as: */ | ||||
/* Xn2 = Xn1 */ | ||||
/* Xn1 = Xn */ | ||||
/* Yn2 = Yn1 */ | ||||
/* Yn1 = acc */ | ||||
/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */ | ||||
/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */ | ||||
state_in = __PKHBT(in, state_in, 16); | ||||
state_out = __PKHBT(out, state_out, 16); | ||||
} | ||||
/* The first stage goes from the input wire to the output wire. */ | ||||
/* Subsequent numStages occur in-place in the output wire */ | ||||
pIn = pDst; | ||||
/* Reset the output pointer */ | ||||
pOut = pDst; | ||||
/* Store the updated state variables back into the state array */ | ||||
*__SIMD32(pState)++ = __PKHBT(state_in, (state_in >> 16), 16); | ||||
*__SIMD32(pState)++ = __PKHBT(state_out, (state_out >> 16), 16); | ||||
/* Decrement the loop counter */ | ||||
stage--; | ||||
} while(stage > 0u); | ||||
} | ||||
/** | ||||
* @} end of BiquadCascadeDF1 group | ||||
*/ | ||||