common.c

/*
freesteam - IAPWS-IF97 steam tables library
Copyright (C) 2004-2005  John Pye

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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/
#define FREESTEAM_BUILDING_LIB
#include "common.h"

/* ipow:  public domain by Mark Stephen with suggestions by Keiichi Nakasato */
MyDouble ipow(MyDouble x, int n){
	MyDouble t = 1.0;

	if(!n)return 1.0;    /* At the top. x^0 = 1 */

	if (n < 0){
		n = -n;
		x = 1.0/x;  /* error if x == 0. Good                        */
	}                 /* ZTC/SC returns inf, which is even better     */

	if (x == 0.0)return 0.0;

	do{
		if(n & 1)t *= x;
		n /= 2;     /* KN prefers if (n/=2) x*=x; This avoids an    */
		x *= x;     /* unnecessary but benign multiplication on     */
	}while(n);      /* the last pass, but the comparison is always
					   true _except_ on the last pass. */

	return t;
}