include/rounding-mode.h

   1 /* Handle floating-point rounding mode within libc.
   2    Copyright (C) 2012-2017 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 _ROUNDING_MODE_H
  20 #define _ROUNDING_MODE_H        1
  21
  22 #include <fenv.h>
  23 #include <stdbool.h>
  24 #include <stdlib.h>
  25
  26 /* Get the architecture-specific definition of how to determine the
  27    rounding mode in libc.  This header must also define the FE_*
  28    macros for any standard rounding modes the architecture does not
  29    have in <fenv.h>, to arbitrary distinct values.  */
  30 #include <get-rounding-mode.h>
  31
  32 /* Return true if a number should be rounded away from zero in
  33    rounding mode MODE, false otherwise.  NEGATIVE is true if the
  34    number is negative, false otherwise.  LAST_DIGIT_ODD is true if the
  35    last digit of the truncated value (last bit for binary) is odd,
  36    false otherwise.  HALF_BIT is true if the number is at least half
  37    way from the truncated value to the next value with the
  38    least-significant digit in the same place, false otherwise.
  39    MORE_BITS is true if the number is not exactly equal to the
  40    truncated value or the half-way value, false otherwise.  */
  41
  42 static bool
  43 round_away (bool negative, bool last_digit_odd, bool half_bit, bool more_bits,
  44             int mode)
  45 {
  46   switch (mode)
  47     {
  48     case FE_DOWNWARD:
  49       return negative && (half_bit || more_bits);
  50
  51     case FE_TONEAREST:
  52       return half_bit && (last_digit_odd || more_bits);
  53
  54     case FE_TOWARDZERO:
  55       return false;
  56
  57     case FE_UPWARD:
  58       return !negative && (half_bit || more_bits);
  59
  60     default:
  61       abort ();
  62     }
  63 }
  64
  65 #endif /* rounding-mode.h */