math/e_scalb.c

   1 /* Copyright (C) 2011-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <math.h>
  20 #include <math_private.h>
  21 #include <libm-alias-finite.h>
  22
  23 static double
  24 __attribute__ ((noinline))
  25 invalid_fn (double x, double fn)
  26 {
  27   if (rint (fn) != fn)
  28     return (fn - fn) / (fn - fn);
  29   else if (fn > 65000.0)
  30     return __scalbn (x, 65000);
  31   else
  32     return __scalbn (x,-65000);
  33 }
  34
  35
  36 double
  37 __ieee754_scalb (double x, double fn)
  38 {
  39   if (__glibc_unlikely (isnan (x)))
  40     return x * fn;
  41   if (__glibc_unlikely (!isfinite (fn)))
  42     {
  43       if (isnan (fn) || fn > 0.0)
  44         return x * fn;
  45       if (x == 0.0)
  46         return x;
  47       return x / -fn;
  48     }
  49   if (__glibc_unlikely (fabs (fn) >= 0x1p31 || (double) (int) fn != fn))
  50     return invalid_fn (x, fn);
  51
  52   return __scalbn (x, (int) fn);
  53 }
  54 libm_alias_finite (__ieee754_scalb, __scalb)