math/e_exp2l.c

   1 /* Compute 2^x.
   2    Copyright (C) 2012-2015 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 <float.h>
  22
  23 /* To avoid spurious underflows, use this definition to treat IBM long
  24    double as approximating an IEEE-style format.  */
  25 #if LDBL_MANT_DIG == 106
  26 # undef LDBL_EPSILON
  27 # define LDBL_EPSILON 0x1p-106L
  28 #endif
  29
  30 long double
  31 __ieee754_exp2l (long double x)
  32 {
  33   if (__glibc_likely (isless (x, (long double) LDBL_MAX_EXP)))
  34     {
  35       if (__builtin_expect (isgreaterequal (x, (long double) (LDBL_MIN_EXP
  36                                                               - LDBL_MANT_DIG
  37                                                               - 1)), 1))
  38         {
  39           int intx = (int) x;
  40           long double fractx = x - intx;
  41           if (fabsl (fractx) < LDBL_EPSILON / 4.0L)
  42             return __scalbnl (1.0L + fractx, intx);
  43           return __scalbnl (__ieee754_expl (M_LN2l * fractx), intx);
  44         }
  45       else
  46         {
  47           /* Underflow or exact zero.  */
  48           if (isinf (x))
  49             return 0;
  50           else
  51             return LDBL_MIN * LDBL_MIN;
  52         }
  53     }
  54   else
  55     /* Infinity, NaN or overflow.  */
  56     return LDBL_MAX * x;
  57 }
  58 strong_alias (__ieee754_exp2l, __exp2l_finite)