// Game_Music_Emu https://bitbucket.org/mpyne/game-music-emu/

#include "Spc_Filter.h"

#include <string.h>

/* Copyright (C) 2007 Shay Green. This module is free software; you
can redistribute it and/or modify it under the terms of the GNU Lesser
General Public License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version. This
module is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
details. You should have received a copy of the GNU Lesser General Public
License along with this module; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */

#include "blargg_source.h"

void SPC_Filter::clear() { memset( ch, 0, sizeof ch ); }

SPC_Filter::SPC_Filter()
{
	enabled = true;
	gain    = gain_unit;
	bass    = bass_norm;
	clear();
}

void SPC_Filter::run( short* io, int count )
{
	require( (count & 1) == 0 ); // must be even

	int const gain = this->gain;
	if ( enabled )
	{
		int const bass = this->bass;
		chan_t* c = &ch [2];
		do
		{
			// cache in registers
			int sum = (--c)->sum;
			int pp1 = c->pp1;
			int p1  = c->p1;

			for ( int i = 0; i < count; i += 2 )
			{
				// Low-pass filter (two point FIR with coeffs 0.25, 0.75)
				int f = io [i] + p1;
				p1 = io [i] * 3;

				// High-pass filter ("leaky integrator")
				int delta = f - pp1;
				pp1 = f;
				int s = sum >> (gain_bits + 2);
				sum += (delta * gain) - (sum >> bass);

				// Clamp to 16 bits
				if ( (short) s != s )
					s = (s >> 31) ^ 0x7FFF;

				io [i] = (short) s;
			}

			c->p1  = p1;
			c->pp1 = pp1;
			c->sum = sum;
			++io;
		}
		while ( c != ch );
	}
	else if ( gain != gain_unit )
	{
		short* const end = io + count;
		while ( io < end )
		{
			int s = (*io * gain) >> gain_bits;
			if ( (short) s != s )
				s = (s >> 31) ^ 0x7FFF;
			*io++ = (short) s;
		}
	}
}
