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/**
* 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 float CBRT2 = 1.25992104989487316477;
static const float CBRT4 = 1.58740105196819947475;
float cbrtf (float x)
{
int e, rem, sign;
float z;
if (!isfinite (x) || x == 0.0F)
return x;
if (x > 0)
sign = 1;
else
{
sign = -1;
x = -x;
}
z = x;
/* extract power of 2, leaving
* mantissa between 0.5 and 1
*/
x = frexpf(x, &e);
/* Approximate cube root of number between .5 and 1,
* peak relative error = 9.2e-6
*/
x = (((-0.13466110473359520655053 * x
+ 0.54664601366395524503440 ) * x
- 0.95438224771509446525043 ) * x
+ 1.1399983354717293273738 ) * x
+ 0.40238979564544752126924;
/* 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 /= CBRT2;
else if (rem == 2)
x /= CBRT4;
e = -e;
}
/* multiply by power of 2 */
x = ldexpf(x, e);
/* Newton iteration */
x -= ( x - (z/(x*x)) ) * 0.333333333333;
if (sign < 0)
x = -x;
return (x);
}
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