1 /* Compute cubic root of float value.
2 Copyright (C) 1997, 2012 Free Software Foundation, Inc.
4 Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
5 Ulrich Drepper <drepper@cygnus.com>, 1997.
7 This program is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
12 This program 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
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>. */
25 /* Code based on glibc/sysdeps/ieee754/flt-32/s_cbrtf.c. */
27 #define CBRT2 1.2599210498948731648 /* 2^(1/3) */
28 #define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
30 static const double factor[5] =
43 if (isfinite (x) && x != 0.0f)
48 /* Reduce X. XM now is an range 1.0 to 0.5. */
49 xm = frexpf (fabsf (x), &xe);
51 u = (0.492659620528969547
52 + (0.697570460207922770 - 0.191502161678719066 * xm) * xm);
56 ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
58 return ldexpf (x > 0.0 ? ym : -ym, xe / 3);