1/* 2 * linear - perform a simple two point 2D linear interpolation 3 * 4 * Copyright (C) 2005-2007,2021 Landon Curt Noll 5 * 6 * Calc is open software; you can redistribute it and/or modify it under 7 * the terms of the version 2.1 of the GNU Lesser General Public License 8 * as published by the Free Software Foundation. 9 * 10 * Calc is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 12 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General 13 * Public License for more details. 14 * 15 * A copy of version 2.1 of the GNU Lesser General Public License is 16 * distributed with calc under the filename COPYING-LGPL. You should have 17 * received a copy with calc; if not, write to Free Software Foundation, Inc. 18 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. 19 * 20 * Under source code control: 2005/12/12 06:41:50 21 * File existed as early as: 2005 22 * 23 * chongo <was here> /\oo/\ http://www.isthe.com/chongo/ 24 * Share and enjoy! :-) http://www.isthe.com/chongo/tech/comp/calc/ 25 */ 26 27/* 28 * linear - perform a simple two point 2D linear interpolation 29 * 30 * given: 31 * x0, y0 first known point on the line 32 * x1, y1 second known point on the line 33 * x a given point to interpolate on 34 * 35 * returns: 36 * y such that (x,y) is on the line defined by (x0,y0) and (x1,y1) 37 * 38 * NOTE: The line cannot be vertical. So x0 != y0. 39 */ 40define linear(x0, y0, x1, y1, x) 41{ 42 /* firewall */ 43 if (!isnum(x0) || ! isnum(y0) || !isnum(x1) || ! isnum(y1) || !isnum(x)) { 44 quit "non-numeric argument passed to linear"; 45 } 46 if (x0 == x1) { 47 quit "linear given a line with an infinite slope"; 48 } 49 50 /* return y = y0 + (delta_Y/delta_X) * (x - x0) */ 51 return y0 + (((y1-y0)/(x1-x0)) * (x - x0)); 52} 53