lib/timespec-sub.c

   1 /* Subtract two struct timespec values.
   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 /* Return the difference between two timespec values A and B.  On
  21    overflow, return an extremal value.  This assumes 0 <= tv_nsec <=
  22    999999999.  */
  23
  24 #include <config.h>
  25 #include "timespec.h"
  26
  27 #include "intprops.h"
  28
  29 struct timespec
  30 timespec_sub (struct timespec a, struct timespec b)
  31 {
  32   struct timespec r;
  33   time_t rs = a.tv_sec;
  34   time_t bs = b.tv_sec;
  35   int ns = a.tv_nsec - b.tv_nsec;
  36   int rns = ns;
  37
  38   if (ns < 0)
  39     {
  40       rns = ns + 1000000000;
  41       if (rs == TYPE_MINIMUM (time_t))
  42         {
  43           if (bs <= 0)
  44             goto low_overflow;
  45           bs--;
  46         }
  47       else
  48         rs--;
  49     }
  50
  51   if (INT_SUBTRACT_OVERFLOW (rs, bs))
  52     {
  53       if (rs < 0)
  54         {
  55         low_overflow:
  56           rs = TYPE_MINIMUM (time_t);
  57           rns = 0;
  58         }
  59       else
  60         {
  61           rs = TYPE_MAXIMUM (time_t);
  62           rns = 999999999;
  63         }
  64     }
  65   else
  66     rs -= bs;
  67
  68   r.tv_sec = rs;
  69   r.tv_nsec = rns;
  70   return r;
  71 }