inet/deadline.c

   1 /* Computing deadlines for timeouts.
   2    Copyright (C) 2017-2019 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <net-internal.h>
  20
  21 #include <assert.h>
  22 #include <limits.h>
  23 #include <stdio.h>
  24 #include <stdint.h>
  25 #include <time.h>
  26
  27 struct deadline_current_time
  28 __deadline_current_time (void)
  29 {
  30   struct deadline_current_time result;
  31   if (__clock_gettime (CLOCK_MONOTONIC, &result.current) != 0)
  32     __clock_gettime (CLOCK_REALTIME, &result.current);
  33   assert (result.current.tv_sec >= 0);
  34   return result;
  35 }
  36
  37 /* A special deadline value for which __deadline_is_infinite is
  38    true.  */
  39 static inline struct deadline
  40 infinite_deadline (void)
  41 {
  42   return (struct deadline) { { -1, -1 } };
  43 }
  44
  45 struct deadline
  46 __deadline_from_timeval (struct deadline_current_time current,
  47                          struct timeval tv)
  48 {
  49   assert (__is_timeval_valid_timeout (tv));
  50
  51   /* Compute second-based deadline.  Perform the addition in
  52      uintmax_t, which is unsigned, to simply overflow detection.  */
  53   uintmax_t sec = current.current.tv_sec;
  54   sec += tv.tv_sec;
  55   if (sec < (uintmax_t) tv.tv_sec)
  56     return infinite_deadline ();
  57
  58   /* Compute nanosecond deadline.  */
  59   int nsec = current.current.tv_nsec + tv.tv_usec * 1000;
  60   if (nsec >= 1000 * 1000 * 1000)
  61     {
  62       /* Carry nanosecond overflow to seconds.  */
  63       nsec -= 1000 * 1000 * 1000;
  64       if (sec + 1 < sec)
  65         return infinite_deadline ();
  66       ++sec;
  67     }
  68   /* This uses a GCC extension, otherwise these casts for detecting
  69      overflow would not be defined.  */
  70   if ((time_t) sec < 0 || sec != (uintmax_t) (time_t) sec)
  71     return infinite_deadline ();
  72
  73   return (struct deadline) { { sec, nsec } };
  74 }
  75
  76 int
  77 __deadline_to_ms (struct deadline_current_time current,
  78                   struct deadline deadline)
  79 {
  80   if (__deadline_is_infinite (deadline))
  81     return INT_MAX;
  82
  83   if (current.current.tv_sec > deadline.absolute.tv_sec
  84       || (current.current.tv_sec == deadline.absolute.tv_sec
  85           && current.current.tv_nsec >= deadline.absolute.tv_nsec))
  86     return 0;
  87   time_t sec = deadline.absolute.tv_sec - current.current.tv_sec;
  88   if (sec >= INT_MAX)
  89     /* This value will overflow below.  */
  90     return INT_MAX;
  91   int nsec = deadline.absolute.tv_nsec - current.current.tv_nsec;
  92   if (nsec < 0)
  93     {
  94       /* Borrow from the seconds field.  */
  95       assert (sec > 0);
  96       --sec;
  97       nsec += 1000 * 1000 * 1000;
  98     }
  99
 100   /* Prepare for rounding up to milliseconds.  */
 101   nsec += 999999;
 102   if (nsec > 1000 * 1000 * 1000)
 103     {
 104       assert (sec < INT_MAX);
 105       ++sec;
 106       nsec -= 1000 * 1000 * 1000;
 107     }
 108
 109   unsigned int msec = nsec / (1000 * 1000);
 110   if (sec > INT_MAX / 1000)
 111     return INT_MAX;
 112   msec += sec * 1000;
 113   if (msec > INT_MAX)
 114     return INT_MAX;
 115   return msec;
 116 }