lib/dtotimespec.c

   1 /* Convert double to timespec.
   2
   3    Copyright (C) 2011-2012 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 /* written by Paul Eggert */
  19
  20 /* Convert the double value SEC to a struct timespec.  Round toward
  21    positive infinity.  On overflow, return an extremal value.  */
  22
  23 #include <config.h>
  24
  25 #include "timespec.h"
  26
  27 #include "intprops.h"
  28
  29 struct timespec
  30 dtotimespec (double sec)
  31 {
  32   enum { BILLION = 1000 * 1000 * 1000 };
  33   double min_representable = TYPE_MINIMUM (time_t);
  34   double max_representable =
  35     ((TYPE_MAXIMUM (time_t) * (double) BILLION + (BILLION - 1))
  36      / BILLION);
  37   struct timespec r;
  38
  39   if (! (min_representable < sec))
  40     {
  41       r.tv_sec = TYPE_MINIMUM (time_t);
  42       r.tv_nsec = 0;
  43     }
  44   else if (! (sec < max_representable))
  45     {
  46       r.tv_sec = TYPE_MAXIMUM (time_t);
  47       r.tv_nsec = BILLION - 1;
  48     }
  49   else
  50     {
  51       time_t s = sec;
  52       double frac = BILLION * (sec - s);
  53       long ns = frac;
  54       ns += ns < frac;
  55       s += ns / BILLION;
  56       ns %= BILLION;
  57
  58       if (ns < 0)
  59         {
  60           s--;
  61           ns += BILLION;
  62         }
  63
  64       r.tv_sec = s;
  65       r.tv_nsec = ns;
  66     }
  67
  68   return r;
  69 }