include/math-narrow-eval.h

   1 /* Narrow floating-point values to their semantic type.
   2    Copyright (C) 2015-2019 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 #ifndef _MATH_NARROW_EVAL_H
  20 #define _MATH_NARROW_EVAL_H     1
  21
  22 #include <float.h>
  23
  24 /* math_narrow_eval reduces its floating-point argument to the range
  25    and precision of its semantic type.  (The original evaluation may
  26    still occur with excess range and precision, so the result may be
  27    affected by double rounding.)  */
  28 #if FLT_EVAL_METHOD == 0
  29 # define math_narrow_eval(x) (x)
  30 #else
  31 # if FLT_EVAL_METHOD == 1
  32 #  define excess_precision(type) __builtin_types_compatible_p (type, float)
  33 # else
  34 #  define excess_precision(type) (__builtin_types_compatible_p (type, float) \
  35                                   || __builtin_types_compatible_p (type, \
  36                                                                    double))
  37 # endif
  38 # define math_narrow_eval(x)                                    \
  39   ({                                                            \
  40     __typeof (x) math_narrow_eval_tmp = (x);                    \
  41     if (excess_precision (__typeof (math_narrow_eval_tmp)))     \
  42       __asm__ ("" : "+m" (math_narrow_eval_tmp));               \
  43     math_narrow_eval_tmp;                                       \
  44    })
  45 #endif
  46
  47 #endif /* math-narrow-eval.h */