math/e_exp2_template.c

   1 /* Compute 2^x.
   2    Copyright (C) 2012-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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 <math-underflow.h>
  22 #include <float.h>
  23
  24 FLOAT
  25 M_DECL_FUNC (__ieee754_exp2) (FLOAT x)
  26 {
  27   if (__glibc_likely (isless (x, (FLOAT) M_MAX_EXP)))
  28     {
  29       if (__builtin_expect (isgreaterequal (x, (FLOAT) (M_MIN_EXP - M_MANT_DIG
  30                                                         - 1)), 1))
  31         {
  32           int intx = (int) x;
  33           FLOAT fractx = x - intx;
  34           FLOAT result;
  35           if (M_FABS (fractx) < M_EPSILON / 4)
  36             result = M_SCALBN (1 + fractx, intx);
  37           else
  38             result = M_SCALBN (M_EXP (M_MLIT (M_LN2) * fractx), intx);
  39           math_check_force_underflow_nonneg (result);
  40           return result;
  41         }
  42       else
  43         {
  44           /* Underflow or exact zero.  */
  45           if (isinf (x))
  46             return 0;
  47           else
  48             return M_MIN * M_MIN;
  49         }
  50     }
  51   else
  52     /* Infinity, NaN or overflow.  */
  53     return M_MAX * x;
  54 }
  55 declare_mgen_finite_alias (__ieee754_exp2, __exp2)