/*
    Copyright (C) 2012-2014 Carl Hetherington <cth@carlh.net>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

#include "modified_gamma_transfer_function.h"
#include <cmath>

using std::pow;
using boost::shared_ptr;
using boost::dynamic_pointer_cast;
using namespace dcp;

ModifiedGammaTransferFunction::ModifiedGammaTransferFunction (double power, double threshold, double A, double B)
	: _power (power)
	, _threshold (threshold)
	, _A (A)
	, _B (B)
{

}

double *
ModifiedGammaTransferFunction::make_lut (int bit_depth, bool inverse) const
{
	int const bit_length = int(std::pow(2.0f, bit_depth));
	double* lut = new double[bit_length];
	if (inverse) {
		double const threshold = _threshold / _B;
		for (int i = 0; i < bit_length; ++i) {
			double const p = static_cast<double> (i) / (bit_length - 1);
			if (p > threshold) {
				lut[i] = (1 + _A) * pow (p, 1 / _power) - _A;
			} else {
				lut[i] = p * _B;
			}
		}
	} else {
		for (int i = 0; i < bit_length; ++i) {
			double const p = static_cast<double> (i) / (bit_length - 1);
			if (p > _threshold) {
				lut[i] = pow ((p + _A) / (1 + _A), _power);
			} else {
				lut[i] = p / _B;
			}
		}
	}

	return lut;
}

bool
ModifiedGammaTransferFunction::about_equal (shared_ptr<const TransferFunction> other, double epsilon) const
{
	shared_ptr<const ModifiedGammaTransferFunction> o = dynamic_pointer_cast<const ModifiedGammaTransferFunction> (other);
	if (!o) {
		return false;
	}

	return (
		fabs (_power - o->_power) < epsilon &&
	        fabs (_threshold - o->_threshold) < epsilon &&
		fabs (_A - o->_A) < epsilon &&
		fabs (_B - o->_B) < epsilon
		);
}