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[glibc.git] / sysdeps / libm-ieee754 / s_csqrtf.c
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1 /* Complex square root of float value.
2 Copyright (C) 1997 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 Library General Public License as
9 published by the Free Software Foundation; either version 2 of the
10 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 Library General Public License for more details.
17 You should have received a copy of the GNU Library General Public
18 License along with the GNU C Library; see the file COPYING.LIB. If not,
19 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
22 #include <complex.h>
23 #include <math.h>
25 #include "math_private.h"
28 __complex__ float
29 __csqrtf (__complex__ float x)
31 __complex__ float 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_VALF;
40 __imag__ res = __imag__ x;
42 else if (rcls == FP_INFINITE)
44 if (__real__ x < 0.0)
46 __real__ res = icls == FP_NAN ? __nanf ("") : 0;
47 __imag__ res = __copysignf (HUGE_VALF, __imag__ x);
49 else
51 __real__ res = __real__ x;
52 __imag__ res = (icls == FP_NAN
53 ? __nanf ("") : __copysignf (0.0, __imag__ x));
56 else
58 __real__ res = __nanf ("");
59 __imag__ res = __nanf ("");
62 else
64 if (icls == FP_ZERO)
66 if (__real__ x < 0.0)
68 __real__ res = 0.0;
69 __imag__ res = __copysignf (__ieee754_sqrtf (-__real__ x),
70 __imag__ x);
72 else
74 __real__ res = fabsf (__ieee754_sqrtf (__real__ x));
75 __imag__ res = __copysignf (0.0, __imag__ x);
78 else if (rcls == FP_ZERO)
80 float r = __ieee754_sqrtf (0.5 * fabsf (__imag__ x));
82 __real__ res = __copysignf (r, __imag__ x);
83 __imag__ res = r;
85 else
87 #if 0 /* FIXME: this is broken. */
88 __complex__ float q;
89 float t, r;
91 if (fabsf (__imag__ x) < 2.0e-4 * fabsf (__real__ x))
92 t = 0.25 * __imag__ x * (__imag__ x / __real__ x);
93 else
94 t = 0.5 * (__ieee754_hypotf (__real__ x, __imag__ x) - __real__ x);
96 r = __ieee754_sqrtf (t);
98 __real__ q = __imag__ x / (2.0 * r);
99 __imag__ q = r;
101 /* Heron iteration in complex arithmetic. */
102 res = 0.5 * (q + q / x);
103 #else
104 float d, imag;
106 d = __ieee754_hypotf (__real__ x, __imag__ x);
107 imag = __ieee754_sqrtf (0.5 * (d - __real__ x));
109 __real__ res = __ieee754_sqrtf (0.5 * (d + __real__ x));
110 __imag__ res = __copysignf (imag, __imag__ x);
111 #endif
115 return res;
117 weak_alias (__csqrtf, csqrtf)