| /* Compute cubic root of double value. |
| Copyright (C) 1997 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Dirk Alboth <dirka@uni-paderborn.de> and |
| Ulrich Drepper <drepper@cygnus.com>, 1997. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, write to the Free |
| Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 02111-1307 USA. */ |
| |
| #include "math.h" |
| #include "math_private.h" |
| |
| |
| #define CBRT2 1.2599210498948731648 /* 2^(1/3) */ |
| #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */ |
| |
| static const double factor[5] = |
| { |
| 1.0 / SQR_CBRT2, |
| 1.0 / CBRT2, |
| 1.0, |
| CBRT2, |
| SQR_CBRT2 |
| }; |
| |
| |
| double |
| __cbrt (double x) |
| { |
| double xm, ym, u, t2; |
| int xe; |
| |
| /* Reduce X. XM now is an range 1.0 to 0.5. */ |
| xm = __frexp (fabs (x), &xe); |
| |
| /* If X is not finite or is null return it (with raising exceptions |
| if necessary. |
| Note: *Our* version of `frexp' sets XE to zero if the argument is |
| Inf or NaN. This is not portable but faster. */ |
| if (xe == 0 && fpclassify (x) <= FP_ZERO) |
| return x + x; |
| |
| u = (0.354895765043919860 |
| + ((1.50819193781584896 |
| + ((-2.11499494167371287 |
| + ((2.44693122563534430 |
| + ((-1.83469277483613086 |
| + (0.784932344976639262 - 0.145263899385486377 * xm) * xm) |
| * xm)) |
| * xm)) |
| * xm)) |
| * xm)); |
| |
| t2 = u * u * u; |
| |
| ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3]; |
| |
| return __ldexp (x > 0.0 ? ym : -ym, xe / 3); |
| } |
| weak_alias (__cbrt, cbrt) |
| #ifdef NO_LONG_DOUBLE |
| strong_alias (__cbrt, __cbrtl) |
| weak_alias (__cbrt, cbrtl) |
| #endif |
