/*
 * (I)RDFT transforms
 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "dsputil.h"

/**
 * @file libavcodec/rdft.c
 * (Inverse) Real Discrete Fourier Transforms.
 */

/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
SINTABLE(16);
SINTABLE(32);
SINTABLE(64);
SINTABLE(128);
SINTABLE(256);
SINTABLE(512);
SINTABLE(1024);
SINTABLE(2048);
SINTABLE(4096);
SINTABLE(8192);
SINTABLE(16384);
SINTABLE(32768);
SINTABLE(65536);

SINTABLE_CONST FFTSample* const ff_sin_tabs[] = {
	NULL,
	NULL,
	NULL,
	NULL,
	ff_sin_16,
	ff_sin_32,
	ff_sin_64,
	ff_sin_128,
	ff_sin_256,
	ff_sin_512,
	ff_sin_1024,
	ff_sin_2048,
	ff_sin_4096,
	ff_sin_8192,
	ff_sin_16384,
	ff_sin_32768,
	ff_sin_65536,
};

av_cold int ff_rdft_init(RDFTContext* s, int nbits, enum RDFTransformType trans)
{
	int n = 1 << nbits;
	const double theta = (trans == RDFT || trans == IRIDFT ? -1 : 1) * 2 * M_PI / n;

	s->nbits = nbits;
	s->inverse = trans == IRDFT || trans == IRIDFT;
	s->sign_convention = trans == RIDFT || trans == IRIDFT ? 1 : -1;

	if (nbits < 4 || nbits > 16)
		return -1;

	if (ff_fft_init(&s->fft, nbits - 1, trans == IRDFT || trans == RIDFT) < 0)
		return -1;

	ff_init_ff_cos_tabs(nbits);
	s->tcos = ff_cos_tabs[nbits];
	s->tsin = ff_sin_tabs[nbits] + (trans == RDFT || trans == IRIDFT) * (n >> 2);
	for (int i = 0; i < (n >> 2); i++) {
		s->tsin[i] = (float) std::sin(i * theta);
	}
	return 0;
}

/** Map one real FFT into two parallel real even and odd FFTs. Then interleave
 * the two real FFTs into one complex FFT. Unmangle the results.
 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
 */
static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
{
	int i, i1, i2;
	FFTComplex ev, od;
	const int n = 1 << s->nbits;
	const float k1 = 0.5;
	const float k2 = (float) (0.5 - s->inverse);
	const FFTSample* tcos = s->tcos;
	const FFTSample* tsin = s->tsin;

	if (!s->inverse) {
		ff_fft_permute(&s->fft, (FFTComplex*) data);
		ff_fft_calc(&s->fft, (FFTComplex*) data);
	}
	/* i=0 is a special case because of packing, the DC term is real, so we
       are going to throw the N/2 term (also real) in with it. */
	ev.re = data[0];
	data[0] = ev.re + data[1];
	data[1] = ev.re - data[1];
	for (i = 1; i < (n >> 2); i++) {
		i1 = 2 * i;
		i2 = n - i1;
		/* Separate even and odd FFTs */
		ev.re = k1 * (data[i1] + data[i2]);
		od.im = -k2 * (data[i1] - data[i2]);
		ev.im = k1 * (data[i1 + 1] - data[i2 + 1]);
		od.re = k2 * (data[i1 + 1] + data[i2 + 1]);
		/* Apply twiddle factors to the odd FFT and add to the even FFT */
		data[i1] = ev.re + od.re * tcos[i] - od.im * tsin[i];
		data[i1 + 1] = ev.im + od.im * tcos[i] + od.re * tsin[i];
		data[i2] = ev.re - od.re * tcos[i] + od.im * tsin[i];
		data[i2 + 1] = -ev.im + od.im * tcos[i] + od.re * tsin[i];
	}
	data[2 * i + 1] = s->sign_convention * data[2 * i + 1];
	if (s->inverse) {
		data[0] *= k1;
		data[1] *= k1;
		ff_fft_permute(&s->fft, (FFTComplex*) data);
		ff_fft_calc(&s->fft, (FFTComplex*) data);
	}
}

void ff_rdft_calc(RDFTContext* s, FFTSample* data)
{
	ff_rdft_calc_c(s, data);
}

av_cold void ff_rdft_end(RDFTContext* s)
{
	ff_fft_end(&s->fft);
}
