Downsampler2xNeon.hpp

/*****************************************************************************

        Downsampler2xNeon.hpp
        Author: Laurent de Soras, 2020

--- Legal stuff ---

This program is free software. It comes without any warranty, to
the extent permitted by applicable law. You can redistribute it
and/or modify it under the terms of the Do What The Fuck You Want
To Public License, Version 2, as published by Sam Hocevar. See
http://sam.zoy.org/wtfpl/COPYING for more details.

*Tab=3***********************************************************************/



#if ! defined (hiir_Downsampler2xNeon_CODEHEADER_INCLUDED)
#define hiir_Downsampler2xNeon_CODEHEADER_INCLUDED



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#include "hiir/fnc_neon.h"
#include "hiir/StageProcNeonV2.h"

#include <arm_neon.h>

#include <cassert>



namespace hiir
{



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/*
==============================================================================
Name: ctor
Throws: Nothing
==============================================================================
*/

template <int NC>
Downsampler2xNeon <NC>::Downsampler2xNeon ()
:	_filter ()
{
	for (int i = 0; i < _nbr_stages + 1; ++i)
	{
		storea (_filter [i]._mem, vdup_n_f32 (0));
	}
	if ((NBR_COEFS & 1) != 0)
	{
		const int      pos = (NBR_COEFS ^ 1) & (_stage_width - 1);
		_filter [_nbr_stages]._coef [pos] = 1;
	}

	clear_buffers ();
}



/*
==============================================================================
Name: set_coefs
Description:
	Sets filter coefficients. Generate them with the PolyphaseIir2Designer
	class.
	Call this function before doing any processing.
Input parameters:
	- coef_arr: Array of coefficients. There should be as many coefficients as
		mentioned in the class template parameter.
Throws: Nothing
==============================================================================
*/

template <int NC>
void	Downsampler2xNeon <NC>::set_coefs (const double coef_arr [])
{
	assert (coef_arr != nullptr);

	for (int i = 0; i < NBR_COEFS; ++i)
	{
		const int      stage = (i / _stage_width) + 1;
		const int      pos   = (i ^ 1) & (_stage_width - 1);
		_filter [stage]._coef [pos] = float (coef_arr [i]);
	}
}



/*
==============================================================================
Name: process_sample
Description:
	Downsamples (x2) one pair of samples, to generate one output sample.
Input parameters:
	- in_ptr: pointer on the two samples to decimate
Returns: Samplerate-reduced sample.
Throws: Nothing
==============================================================================
*/

template <int NC>
float	Downsampler2xNeon <NC>::process_sample (const float in_ptr [2])
{
	assert (in_ptr != nullptr);

	auto           x = load2u (in_ptr);
	StageProcNeonV2 <_nbr_stages>::process_sample_pos (x, &_filter [0]);
#if 0
	const float    out = vget_lane_f32 (vpadd_f32 (x, x), 0);
#else
	const float    out = vget_lane_f32 (x, 1) + vget_lane_f32 (x, 0);
#endif

	return out * 0.5f;
}



/*
==============================================================================
Name: process_block
Description:
	Downsamples (x2) a block of samples.
	Input and output blocks may overlap, see assert() for details.
Input parameters:
	- in_ptr: Input array, containing nbr_spl * 2 samples.
	- nbr_spl: Number of samples to output, > 0
Output parameters:
	- out_ptr: Array for the output samples, capacity: nbr_spl samples.
Throws: Nothing
==============================================================================
*/

template <int NC>
void	Downsampler2xNeon <NC>::process_block (float out_ptr [], const float in_ptr [], long nbr_spl)
{
	assert (in_ptr  != nullptr);
	assert (out_ptr != nullptr);
	assert (out_ptr <= in_ptr || out_ptr >= in_ptr + nbr_spl * 2);
	assert (nbr_spl > 0);

	long           pos = 0;
	do
	{
		out_ptr [pos] = process_sample (in_ptr + pos * 2);
		++ pos;
	}
	while (pos < nbr_spl);
}



/*
==============================================================================
Name: process_sample_split
Description:
	Split (spectrum-wise) in half a pair of samples. The lower part of the
	spectrum is a classic downsampling, equivalent to the output of
	process_sample().
	The higher part is the complementary signal: original filter response
	is flipped from left to right, becoming a high-pass filter with the same
	cutoff frequency. This signal is then critically sampled (decimation by 2),
	flipping the spectrum: Fs/4...Fs/2 becomes Fs/4...0.
Input parameters:
	- in_ptr: pointer on the pair of input samples
Output parameters:
	- low: output sample, lower part of the spectrum (downsampling)
	- high: output sample, higher part of the spectrum.
Throws: Nothing
==============================================================================
*/

template <int NC>
void	Downsampler2xNeon <NC>::process_sample_split (float &low, float &high, const float in_ptr [2])
{
	assert (in_ptr != nullptr);

	auto           x  = load2u (in_ptr);
	StageProcNeonV2 <_nbr_stages>::process_sample_pos (x, &_filter [0]);
	x   *= vdup_n_f32 (0.5f);
	const float    x0 = vget_lane_f32 (x, 0);
	const float    x1 = vget_lane_f32 (x, 1);
	low  = x1 + x0;
	high = x1 - x0;
}



/*
==============================================================================
Name: process_block_split
Description:
	Split (spectrum-wise) in half a block of samples. The lower part of the
	spectrum is a classic downsampling, equivalent to the output of
	process_block().
	The higher part is the complementary signal: original filter response
	is flipped from left to right, becoming a high-pass filter with the same
	cutoff frequency. This signal is then critically sampled (decimation by 2),
	flipping the spectrum: Fs/4...Fs/2 becomes Fs/4...0.
	Input and output blocks may overlap, see assert() for details.
Input parameters:
	- in_ptr: Input array, containing nbr_spl * 2 samples.
	- nbr_spl: Number of samples for each output, > 0
Output parameters:
	- out_l_ptr: Array for the output samples, lower part of the spectrum
		(downsampling). Capacity: nbr_spl samples.
	- out_h_ptr: Array for the output samples, higher part of the spectrum.
		Capacity: nbr_spl samples.
Throws: Nothing
==============================================================================
*/

template <int NC>
void	Downsampler2xNeon <NC>::process_block_split (float out_l_ptr [], float out_h_ptr [], const float in_ptr [], long nbr_spl)
{
	assert (in_ptr    != nullptr);
	assert (out_l_ptr != nullptr);
	assert (out_l_ptr <= in_ptr || out_l_ptr >= in_ptr + nbr_spl * 2);
	assert (out_h_ptr != nullptr);
	assert (out_h_ptr <= in_ptr || out_h_ptr >= in_ptr + nbr_spl * 2);
	assert (out_h_ptr != out_l_ptr);
	assert (nbr_spl > 0);

	long           pos = 0;
	do
	{
		process_sample_split (out_l_ptr [pos], out_h_ptr [pos], in_ptr + pos * 2);
		++ pos;
	}
	while (pos < nbr_spl);
}



/*
==============================================================================
Name: clear_buffers
Description:
	Clears filter memory, as if it processed silence since an infinite amount
	of time.
Throws: Nothing
==============================================================================
*/

template <int NC>
void	Downsampler2xNeon <NC>::clear_buffers ()
{
	for (int i = 0; i < _nbr_stages + 1; ++i)
	{
		storea (_filter [i]._mem, vdup_n_f32 (0));
	}
}



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}  // namespace hiir



#endif   // hiir_Downsampler2xNeon_CODEHEADER_INCLUDED



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