1 /* Complex square root of double value. 2 Copyright (C) 1997, 1998 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 Based on an algorithm by Stephen L. Moshier <moshier@world.std.com>. 5 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997. 6 7 The GNU C Library is free software; you can redistribute it and/or 8 modify it under the terms of the GNU Lesser General Public 9 License as published by the Free Software Foundation; either 10 version 2.1 of the License, or (at your option) any later version. 11 12 The GNU C Library is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 Lesser General Public License for more details. 16 17 You should have received a copy of the GNU Lesser General Public 18 License along with the GNU C Library; if not, write to the Free 19 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 20 02111-1307 USA. */ 21 22 #include <complex.h> 23 #include <math.h> 24 25 #include "math_private.h" 26 27 28 __complex__ double 29 __csqrt (__complex__ double x) 30 { 31 __complex__ double res; 32 int rcls = fpclassify (__real__ x); 33 int icls = fpclassify (__imag__ x); 34 35 if (rcls <= FP_INFINITE || icls <= FP_INFINITE) 36 { 37 if (icls == FP_INFINITE) 38 { 39 __real__ res = HUGE_VAL; 40 __imag__ res = __imag__ x; 41 } 42 else if (rcls == FP_INFINITE) 43 { 44 if (__real__ x < 0.0) 45 { 46 __real__ res = icls == FP_NAN ? nan ("") : 0; 47 __imag__ res = copysign (HUGE_VAL, __imag__ x); 48 } 49 else 50 { 51 __real__ res = __real__ x; 52 __imag__ res = (icls == FP_NAN 53 ? nan ("") : copysign (0.0, __imag__ x)); 54 } 55 } 56 else 57 { 58 __real__ res = nan (""); 59 __imag__ res = nan (""); 60 } 61 } 62 else 63 { 64 if (icls == FP_ZERO) 65 { 66 if (__real__ x < 0.0) 67 { 68 __real__ res = 0.0; 69 __imag__ res = copysign (sqrt (-__real__ x), 70 __imag__ x); 71 } 72 else 73 { 74 __real__ res = fabs (sqrt (__real__ x)); 75 __imag__ res = copysign (0.0, __imag__ x); 76 } 77 } 78 else if (rcls == FP_ZERO) 79 { 80 double r = sqrt (0.5 * fabs (__imag__ x)); 81 82 __real__ res = copysign (r, __imag__ x); 83 __imag__ res = r; 84 } 85 else 86 { 87 double d, r, s; 88 89 d = hypot (__real__ x, __imag__ x); 90 /* Use the identity 2 Re res Im res = Im x 91 to avoid cancellation error in d +/- Re x. */ 92 if (__real__ x > 0) 93 { 94 r = sqrt (0.5 * d + 0.5 * __real__ x); 95 s = (0.5 * __imag__ x) / r; 96 } 97 else 98 { 99 s = sqrt (0.5 * d - 0.5 * __real__ x); 100 r = fabs ((0.5 * __imag__ x) / s); 101 } 102 103 __real__ res = r; 104 __imag__ res = copysign (s, __imag__ x); 105 } 106 } 107 108 return res; 109 } 110 weak_alias (__csqrt, csqrt) 111 #ifdef NO_LONG_DOUBLE 112 strong_alias (__csqrt, __csqrtl) 113 weak_alias (__csqrt, csqrtl) 114 #endif 115