projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 26dee9c4 | 1 | /* Compute cubic root of double value. |
| 04277e02 | 2 | Copyright (C) 1997-2019 Free Software Foundation, Inc. |
| 26dee9c4 UD |
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. | |
| f7eac6eb | 6 | |
| 26dee9c4 | 7 | The GNU C Library is free software; you can redistribute it and/or |
| 41bdb6e2 AJ |
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. | |
| 26dee9c4 UD |
11 | |
| 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 | |
| 41bdb6e2 | 15 | Lesser General Public License for more details. |
| 26dee9c4 | 16 | |
| 41bdb6e2 | 17 | You should have received a copy of the GNU Lesser General Public |
| 59ba27a6 | 18 | License along with the GNU C Library; if not, see |
| 5a82c748 | 19 | <https://www.gnu.org/licenses/>. */ |
| f7eac6eb | 20 | |
| 1ed0291c | 21 | #include <math.h> |
| 1e2bffd0 | 22 | #include <libm-alias-double.h> |
| f7eac6eb | 23 | |
| f7eac6eb | 24 | |
| 26dee9c4 UD |
25 | #define CBRT2 1.2599210498948731648 /* 2^(1/3) */ |
| 26 | #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */ | |
| f7eac6eb | 27 | |
| 26dee9c4 | 28 | static const double factor[5] = |
| f7eac6eb | 29 | { |
| 26dee9c4 UD |
30 | 1.0 / SQR_CBRT2, |
| 31 | 1.0 / CBRT2, | |
| 32 | 1.0, | |
| 33 | CBRT2, | |
| 34 | SQR_CBRT2 | |
| 35 | }; | |
| f7eac6eb | 36 | |
| f7eac6eb | 37 | |
| 26dee9c4 UD |
38 | double |
| 39 | __cbrt (double x) | |
| 40 | { | |
| 41 | double xm, ym, u, t2; | |
| 42 | int xe; | |
| f7eac6eb | 43 | |
| 26dee9c4 UD |
44 | /* Reduce X. XM now is an range 1.0 to 0.5. */ |
| 45 | xm = __frexp (fabs (x), &xe); | |
| f7eac6eb | 46 | |
| 26dee9c4 | 47 | /* If X is not finite or is null return it (with raising exceptions |
| dd7d45e8 UD |
48 | if necessary. |
| 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) | |
| 26dee9c4 | 52 | return x + x; |
| f7eac6eb | 53 | |
| c5d5d574 OB |
54 | u = (0.354895765043919860 |
| 55 | + ((1.50819193781584896 | |
| 56 | + ((-2.11499494167371287 | |
| 57 | + ((2.44693122563534430 | |
| 58 | + ((-1.83469277483613086 | |
| 59 | + (0.784932344976639262 - 0.145263899385486377 * xm) | |
| 60 | * xm) | |
| 61 | * xm)) | |
| 26dee9c4 | 62 | * xm)) |
| c5d5d574 OB |
63 | * xm)) |
| 64 | * xm)); | |
| f7eac6eb | 65 | |
| 26dee9c4 | 66 | t2 = u * u * u; |
| f7eac6eb | 67 | |
| 26dee9c4 | 68 | ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3]; |
| f7eac6eb | 69 | |
| 26dee9c4 | 70 | return __ldexp (x > 0.0 ? ym : -ym, xe / 3); |
| f7eac6eb | 71 | } |
| 1e2bffd0 | 72 | libm_alias_double (__cbrt, cbrt) |