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 <config.h>
  26 #include "timespec.h"
  27
  28 #include "intprops.h"
  29
  30 struct timespec
  31 timespec_sub (struct timespec a, struct timespec b)
  32 {
  33   struct timespec r;
  34   time_t rs = a.tv_sec;
  35   time_t bs = b.tv_sec;
  36   int ns = a.tv_nsec - b.tv_nsec;
  37   int rns = ns;
  38
  39   if (ns < 0)
  40     {
  41       rns = ns + 1000000000;
  42       if (rs == TYPE_MINIMUM (time_t))
  43         {
  44           if (bs <= 0)
  45             goto low_overflow;
  46           bs--;
  47         }
  48       else
  49         rs--;
  50     }
  51
  52   if (INT_SUBTRACT_OVERFLOW (rs, bs))
  53     {
  54       if (rs < 0)
  55         {
  56         low_overflow:
  57           rs = TYPE_MINIMUM (time_t);
  58           rns = 0;
  59         }
  60       else
  61         {
  62           rs = TYPE_MAXIMUM (time_t);
  63           rns = 999999999;
  64         }
  65     }
  66   else
  67     rs -= bs;
  68
  69   r.tv_sec = rs;
  70   r.tv_nsec = rns;
  71   return r;
  72 }