mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-23 05:20:06 +00:00
64 lines
1.8 KiB
C
64 lines
1.8 KiB
C
/* Compute cubic root of float 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, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#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
|
|
};
|
|
|
|
|
|
float
|
|
__cbrtf (float x)
|
|
{
|
|
float xm, ym, u, t2;
|
|
int xe;
|
|
|
|
/* Reduce X. XM now is an range 1.0 to 0.5. */
|
|
xm = __frexpf (fabsf (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 = (0.492659620528969547 + (0.697570460207922770
|
|
- 0.191502161678719066 * xm) * xm);
|
|
|
|
t2 = u * u * u;
|
|
|
|
ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
|
|
|
|
return __ldexpf (x > 0.0 ? ym : -ym, xe / 3);
|
|
}
|
|
weak_alias (__cbrtf, cbrtf)
|