1 /* Hypotenuse of a right-angled triangle. 2 Copyright (C) 2012-2021 Free Software Foundation, Inc. 3 4 This file is free software: you can redistribute it and/or modify 5 it under the terms of the GNU Lesser General Public License as 6 published by the Free Software Foundation; either version 3 of the 7 License, or (at your option) any later version. 8 9 This file is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public License 15 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 16 17 /* Written by Bruno Haible <bruno@clisp.org>, 2012. */ 18 19 #include <config.h> 20 21 /* Specification. */ 22 #include <math.h> 23 24 double 25 hypot (double x, double y) /* */ 26 { 27 if (isfinite (x) && isfinite (y)) 28 { 29 /* Determine absolute values. */ 30 x = fabs (x); 31 y = fabs (y); 32 33 { 34 /* Find the bigger and the smaller one. */ 35 double a; 36 double b; 37 38 if (x >= y) 39 { 40 a = x; 41 b = y; 42 } 43 else 44 { 45 a = y; 46 b = x; 47 } 48 /* Now 0 <= b <= a. */ 49 50 { 51 int e; 52 double an; 53 double bn; 54 55 /* Write a = an * 2^e, b = bn * 2^e with 0 <= bn <= an < 1. */ 56 an = frexp (a, &e); 57 bn = ldexp (b, - e); 58 59 { 60 double cn; 61 62 /* Through the normalization, no unneeded overflow or underflow 63 will occur here. */ 64 cn = sqrt (an * an + bn * bn); 65 return ldexp (cn, e); 66 } 67 } 68 } 69 } 70 else 71 { 72 if (isinf (x) || isinf (y)) 73 /* x or y is infinite. Return +Infinity. */ 74 return HUGE_VAL; 75 else 76 /* x or y is NaN. Return NaN. */ 77 return x + y; 78 } 79 }