libquadmath/math/exp2q.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 "quadmath-imp.h"
  20
  21 __float128
  22 exp2q (__float128 x)
  23 {
  24   if (__glibc_likely (__builtin_isless (x, (__float128) FLT128_MAX_EXP)))
  25     {
  26       if (__builtin_expect (__builtin_isgreaterequal (x, (__float128) (FLT128_MIN_EXP - FLT128_MANT_DIG
  27                                                         - 1)), 1))
  28         {
  29           int intx = (int) x;
  30           __float128 fractx = x - intx;
  31           __float128 result;
  32           if (fabsq (fractx) < FLT128_EPSILON / 4)
  33             result = scalbnq (1 + fractx, intx);
  34           else
  35             result = scalbnq (expq (M_LN2q * fractx), intx);
  36           math_check_force_underflow_nonneg (result);
  37           return result;
  38         }
  39       else
  40         {
  41           /* Underflow or exact zero.  */
  42           if (isinfq (x))
  43             return 0;
  44           else
  45             return FLT128_MIN * FLT128_MIN;
  46         }
  47     }
  48   else
  49     /* Infinity, NaN or overflow.  */
  50     return FLT128_MAX * x;
  51 }