mirror of
https://git.code.sf.net/p/mingw-w64/mingw-w64
synced 2024-11-28 04:13:26 +08:00
8a67ab4541
Also replace 'This file is a part of' by 'This file is part of' for consistency git-svn-id: svn+ssh://svn.code.sf.net/p/mingw-w64/code/trunk@5147 4407c894-4637-0410-b4f5-ada5f102cad1
105 lines
1.9 KiB
C
105 lines
1.9 KiB
C
/**
|
|
* This file has no copyright assigned and is placed in the Public Domain.
|
|
* This file is part of the mingw-w64 runtime package.
|
|
* No warranty is given; refer to the file DISCLAIMER.PD within this package.
|
|
*/
|
|
#include <math.h>
|
|
#include "cephes_mconf.h"
|
|
|
|
static const double CBRT2 = 1.2599210498948731647672;
|
|
static const double CBRT4 = 1.5874010519681994747517;
|
|
static const double CBRT2I = 0.79370052598409973737585;
|
|
static const double CBRT4I = 0.62996052494743658238361;
|
|
|
|
#ifndef __MINGW32__
|
|
extern double frexp ( double, int * );
|
|
extern double ldexp ( double, int );
|
|
extern int isnan ( double );
|
|
extern int isfinite ( double );
|
|
#endif
|
|
|
|
double cbrt(double x)
|
|
{
|
|
int e, rem, sign;
|
|
double z;
|
|
|
|
#ifdef __MINGW32__
|
|
if (!isfinite (x) || x == 0)
|
|
return x;
|
|
#else
|
|
#ifdef NANS
|
|
if (isnan(x))
|
|
return x;
|
|
#endif
|
|
#ifdef INFINITIES
|
|
if (!isfinite(x))
|
|
return x;
|
|
#endif
|
|
if (x == 0)
|
|
return (x);
|
|
#endif /* __MINGW32__ */
|
|
|
|
if (x > 0)
|
|
sign = 1;
|
|
else
|
|
{
|
|
sign = -1;
|
|
x = -x;
|
|
}
|
|
|
|
z = x;
|
|
/* extract power of 2, leaving
|
|
* mantissa between 0.5 and 1
|
|
*/
|
|
x = frexp(x, &e);
|
|
|
|
/* Approximate cube root of number between .5 and 1,
|
|
* peak relative error = 9.2e-6
|
|
*/
|
|
x = (((-1.3466110473359520655053e-1 * x
|
|
+ 5.4664601366395524503440e-1) * x
|
|
- 9.5438224771509446525043e-1) * x
|
|
+ 1.1399983354717293273738e0 ) * x
|
|
+ 4.0238979564544752126924e-1;
|
|
|
|
/* exponent divided by 3 */
|
|
if (e >= 0)
|
|
{
|
|
rem = e;
|
|
e /= 3;
|
|
rem -= 3*e;
|
|
if (rem == 1)
|
|
x *= CBRT2;
|
|
else if (rem == 2)
|
|
x *= CBRT4;
|
|
}
|
|
/* argument less than 1 */
|
|
else
|
|
{
|
|
e = -e;
|
|
rem = e;
|
|
e /= 3;
|
|
rem -= 3*e;
|
|
if (rem == 1)
|
|
x *= CBRT2I;
|
|
else if (rem == 2)
|
|
x *= CBRT4I;
|
|
e = -e;
|
|
}
|
|
|
|
/* multiply by power of 2 */
|
|
x = ldexp(x, e);
|
|
|
|
/* Newton iteration */
|
|
x -= ( x - (z/(x*x)) )*0.33333333333333333333;
|
|
#ifdef DEC
|
|
x -= ( x - (z/(x*x)) )/3.0;
|
|
#else
|
|
x -= ( x - (z/(x*x)) )*0.33333333333333333333;
|
|
#endif
|
|
|
|
if (sign < 0)
|
|
x = -x;
|
|
return (x);
|
|
}
|