1 /* Compute cubic root of float value.
2 Copyright (C) 1997-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
20 #include <libm-alias-float.h>
23 #define CBRT2 1.2599210498948731648 /* 2^(1/3) */
24 #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
26 static const double factor
[5] =
42 /* Reduce X. XM now is an range 1.0 to 0.5. */
43 xm
= __frexpf (fabsf (x
), &xe
);
45 /* If X is not finite or is null return it (with raising exceptions
47 Note: *Our* version of `frexp' sets XE to zero if the argument is
48 Inf or NaN. This is not portable but faster. */
49 if (xe
== 0 && fpclassify (x
) <= FP_ZERO
)
52 u
= (0.492659620528969547 + (0.697570460207922770
53 - 0.191502161678719066 * xm
) * xm
);
57 ym
= u
* (t2
+ 2.0 * xm
) / (2.0 * t2
+ xm
) * factor
[2 + xe
% 3];
59 return __ldexpf (x
> 0.0 ? ym
: -ym
, xe
/ 3);
61 libm_alias_float (__cbrt
, cbrt
)