math/e_exp2_template.c

   1 /* Compute 2^x.
   2    Copyright (C) 2012-2018 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    <http://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 #define declare_mgen_finite_alias_x(from, to) \
  25         strong_alias (from, to ## _finite)
  26 #define declare_mgen_finite_alias_s(from,to) \
  27         declare_mgen_finite_alias_x (from, to)
  28 #define declare_mgen_finite_alias(from, to) \
  29         declare_mgen_finite_alias_s (M_SUF (from), M_SUF (to))
  30
  31 FLOAT
  32 M_DECL_FUNC (__ieee754_exp2) (FLOAT x)
  33 {
  34   if (__glibc_likely (isless (x, (FLOAT) M_MAX_EXP)))
  35     {
  36       if (__builtin_expect (isgreaterequal (x, (FLOAT) (M_MIN_EXP - M_MANT_DIG
  37                                                         - 1)), 1))
  38         {
  39           int intx = (int) x;
  40           FLOAT fractx = x - intx;
  41           FLOAT result;
  42           if (M_FABS (fractx) < M_EPSILON / 4)
  43             result = M_SCALBN (1 + fractx, intx);
  44           else
  45             result = M_SCALBN (M_EXP (M_MLIT (M_LN2) * fractx), intx);
  46           math_check_force_underflow_nonneg (result);
  47           return result;
  48         }
  49       else
  50         {
  51           /* Underflow or exact zero.  */
  52           if (isinf (x))
  53             return 0;
  54           else
  55             return M_MIN * M_MIN;
  56         }
  57     }
  58   else
  59     /* Infinity, NaN or overflow.  */
  60     return M_MAX * x;
  61 }
  62 declare_mgen_finite_alias (__ieee754_exp2, __exp2)