kc3-lang/gnulib/lib/cbrt.c

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• Hash : 32a72f45
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  Date : 2023-01-01T01:14:21
  

  maint: run 'make update-copyright'
  

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• lib/cbrt.c

• /* Compute cubic root of double value.
     Copyright (C) 1997, 2012-2023 Free Software Foundation, Inc.
  
     Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
     Ulrich Drepper <drepper@cygnus.com>, 1997.
  
     This file 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 3 of the
     License, or (at your option) any later version.
  
     This file 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */
  
  #include <config.h>
  
  /* Specification.  */
  #include <math.h>
  
  /* MSVC with option -fp:strict refuses to compile constant initializers that
     contain floating-point operations.  Pacify this compiler.  */
  #if defined _MSC_VER && !defined __clang__
  # pragma fenv_access (off)
  #endif
  
  /* Code based on glibc/sysdeps/ieee754/dbl-64/s_cbrt.c.  */
  
  #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
  };
  
  
  double
  cbrt (double x)
  {
    if (isfinite (x) && x != 0.0)
      {
        double xm, ym, u, t2;
        int xe;
  
        /* Reduce X.  XM now is an range 1.0 to 0.5.  */
        xm = frexp (fabs (x), &xe);
  
        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);
      }
    else
      return x + x;
  }
  

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