Update.
[glibc.git] / sysdeps / libm-ieee754 / s_cbrt.c
bloba5033ff468f63d2ba00fd7d00fa4ece261243471
1 /* Compute cubic root of double value.
2 Copyright (C) 1997 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
5 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 "math.h"
23 #include "math_private.h"
26 #define CBRT2 1.2599210498948731648 /* 2^(1/3) */
27 #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
29 static const double factor[5] =
31 1.0 / SQR_CBRT2,
32 1.0 / CBRT2,
33 1.0,
34 CBRT2,
35 SQR_CBRT2
39 double
40 __cbrt (double x)
42 double xm, ym, u, t2;
43 int xe;
45 /* Reduce X. XM now is an range 1.0 to 0.5. */
46 xm = __frexp (fabs (x), &xe);
48 /* If X is not finite or is null return it (with raising exceptions
49 if necessary. */
50 if (xe == 0)
51 return x + x;
53 u = (0.354895765043919860
54 + ((1.50819193781584896
55 + ((-2.11499494167371287
56 + ((2.44693122563534430
57 + ((-1.83469277483613086
58 + (0.784932344976639262 - 0.145263899385486377 * xm) * xm)
59 * xm))
60 * xm))
61 * xm))
62 * xm));
64 t2 = u * u * u;
66 ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
68 return __ldexp (x > 0.0 ? ym : -ym, xe / 3);
70 weak_alias (__cbrt, cbrt)
71 #ifdef NO_LONG_DOUBLE
72 strong_alias (__cbrt, __cbrtl)
73 weak_alias (__cbrt, cbrtl)
74 #endif