mk_xy2pix.c

/* -----------------------------------------------------------------------------
 *
 *  Copyright (C) 1997-2010 Krzysztof M. Gorski, Eric Hivon,
 *                          Benjamin D. Wandelt, Anthony J. Banday,
 *                          Matthias Bartelmann,
 *                          Reza Ansari & Kenneth M. Ganga
 *
 *
 *  This file is part of HEALPix.
 *
 *  HEALPix 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.
 *
 *  HEALPix 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 HEALPix; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 *  For more information about HEALPix see http://healpix.jpl.nasa.gov
 *
 *----------------------------------------------------------------------------- */
/* Standard Includes */
#include <math.h>

#include "chealpix.h"

void
mk_xy2pix(int *x2pix, int *y2pix)
{
	/*
	 * =======================================================================
	 * subroutine mk_xy2pix
	 * =======================================================================
	 * sets the array giving the number of the pixel lying in (x,y) x and y
	 * are in {1,128} the pixel number is in {0,128**2-1}
	 *
	 * if  i-1 = sum_p=0  b_p * 2^p then ix = sum_p=0  b_p * 4^p iy = 2*ix ix
	 * + iy in {0, 128**2 -1}
	 * =======================================================================
	 */
	int			i,
				K,
				IP,
				I,
				J,
				ID;

	for (i = 0; i < 127; i++)
		x2pix[i] = 0;
	for (I = 1; I <= 128; I++)
	{
		J = I - 1;
		//!pixel numbers
			K = 0;
		//
			IP = 1;
		//
truc:		if (J == 0)
		{
			x2pix[I - 1] = K;
			y2pix[I - 1] = 2 * K;
		}
		else
		{
			ID = (int) fmod(J, 2);
			J = J / 2;
			K = IP * ID + K;
			IP = IP * 4;
			goto truc;
		}
	}

}