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glibc  2.9
Defines | Functions | Variables
s_cbrt.c File Reference
#include "math.h"
#include "math_private.h"
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Go to the source code of this file.

Defines

#define CBRT2   1.2599210498948731648 /* 2^(1/3) */
#define SQR_CBRT2   1.5874010519681994748 /* 2^(2/3) */

Functions

double __cbrt (double x)

Variables

static const double factor [5]

Define Documentation

#define CBRT2   1.2599210498948731648 /* 2^(1/3) */

Definition at line 26 of file s_cbrt.c.

#define SQR_CBRT2   1.5874010519681994748 /* 2^(2/3) */

Definition at line 27 of file s_cbrt.c.


Function Documentation

double __cbrt ( double  x)

Definition at line 40 of file s_cbrt.c.

{
  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);
}

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Variable Documentation

const double factor[5] [static]
Initial value:
{
  1.0 / SQR_CBRT2,
  1.0 / CBRT2,
  1.0,
  CBRT2,
  SQR_CBRT2
}

Definition at line 29 of file s_cbrt.c.