1 /* Compute cubic root of float value.
2 Copyright (C) 1997-2016 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 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, see
19 <http://www.gnu.org/licenses/>. */
22 #include <math_private.h>
25 #define CBRT2 1.2599210498948731648 /* 2^(1/3) */
26 #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
28 static const double factor
[5] =
44 /* Reduce X. XM now is an range 1.0 to 0.5. */
45 xm
= __frexpf (fabsf (x
), &xe
);
47 /* If X is not finite or is null return it (with raising exceptions
49 Note: *Our* version of `frexp' sets XE to zero if the argument is
50 Inf or NaN. This is not portable but faster. */
51 if (xe
== 0 && fpclassify (x
) <= FP_ZERO
)
54 u
= (0.492659620528969547 + (0.697570460207922770
55 - 0.191502161678719066 * xm
) * xm
);
59 ym
= u
* (t2
+ 2.0 * xm
) / (2.0 * t2
+ xm
) * factor
[2 + xe
% 3];
61 return __ldexpf (x
> 0.0 ? ym
: -ym
, xe
/ 3);
63 weak_alias (__cbrtf
, cbrtf
)