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[glibc/history.git] / math / s_csqrt.c
blob04ed410a16ff9f569eb67d2357a800f2aa513cb0
1 /* Complex square root of double value.
2 Copyright (C) 1997, 1998, 2005 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.
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.
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.
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. */
22 #include <complex.h>
23 #include <math.h>
25 #include "math_private.h"
28 __complex__ double
29 __csqrt (__complex__ double x)
31 __complex__ double res;
32 int rcls = fpclassify (__real__ x);
33 int icls = fpclassify (__imag__ x);
35 if (rcls <= FP_INFINITE || icls <= FP_INFINITE)
37 if (icls == FP_INFINITE)
39 __real__ res = HUGE_VAL;
40 __imag__ res = __imag__ x;
42 else if (rcls == FP_INFINITE)
44 if (__real__ x < 0.0)
46 __real__ res = icls == FP_NAN ? __nan ("") : 0;
47 __imag__ res = __copysign (HUGE_VAL, __imag__ x);
49 else
51 __real__ res = __real__ x;
52 __imag__ res = (icls == FP_NAN
53 ? __nan ("") : __copysign (0.0, __imag__ x));
56 else
58 __real__ res = __nan ("");
59 __imag__ res = __nan ("");
62 else
64 if (icls == FP_ZERO)
66 if (__real__ x < 0.0)
68 __real__ res = 0.0;
69 __imag__ res = __copysign (__ieee754_sqrt (-__real__ x),
70 __imag__ x);
72 else
74 __real__ res = fabs (__ieee754_sqrt (__real__ x));
75 __imag__ res = __copysign (0.0, __imag__ x);
78 else if (rcls == FP_ZERO)
80 double r = __ieee754_sqrt (0.5 * fabs (__imag__ x));
82 __real__ res = r;
83 __imag__ res = __copysign (r, __imag__ x);
85 else
87 double d, r, s;
89 d = __ieee754_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)
94 r = __ieee754_sqrt (0.5 * d + 0.5 * __real__ x);
95 s = (0.5 * __imag__ x) / r;
97 else
99 s = __ieee754_sqrt (0.5 * d - 0.5 * __real__ x);
100 r = fabs ((0.5 * __imag__ x) / s);
103 __real__ res = r;
104 __imag__ res = __copysign (s, __imag__ x);
108 return res;
110 weak_alias (__csqrt, csqrt)
111 #ifdef NO_LONG_DOUBLE
112 strong_alias (__csqrt, __csqrtl)
113 weak_alias (__csqrt, csqrtl)
114 #endif