lib/gettimeofday.c

   1 /* Provide gettimeofday for systems that don't have it or for which it's broken.
   2
   3    Copyright (C) 2001-2003, 2005-2007, 2009-2017 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, or (at your option)
   8    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 Jim Meyering */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include <sys/time.h>
  24
  25 #include <time.h>
  26
  27 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  28 # define WINDOWS_NATIVE
  29 # include <windows.h>
  30 #endif
  31
  32 #include "localtime-buffer.h"
  33
  34 #ifdef WINDOWS_NATIVE
  35
  36 /* GetSystemTimePreciseAsFileTime was introduced only in Windows 8.  */
  37 typedef void (WINAPI * GetSystemTimePreciseAsFileTimeFuncType) (FILETIME *lpTime);
  38 static GetSystemTimePreciseAsFileTimeFuncType GetSystemTimePreciseAsFileTimeFunc = NULL;
  39 static BOOL initialized = FALSE;
  40
  41 static void
  42 initialize (void)
  43 {
  44   HMODULE kernel32 = LoadLibrary ("kernel32.dll");
  45   if (kernel32 != NULL)
  46     {
  47       GetSystemTimePreciseAsFileTimeFunc =
  48         (GetSystemTimePreciseAsFileTimeFuncType) GetProcAddress (kernel32, "GetSystemTimePreciseAsFileTime");
  49     }
  50   initialized = TRUE;
  51 }
  52
  53 #endif
  54
  55 /* This is a wrapper for gettimeofday.  It is used only on systems
  56    that lack this function, or whose implementation of this function
  57    causes problems.
  58    Work around the bug in some systems whereby gettimeofday clobbers
  59    the static buffer that localtime uses for its return value.  The
  60    gettimeofday function from Mac OS X 10.0.4 (i.e., Darwin 1.3.7) has
  61    this problem.  */
  62
  63 int
  64 gettimeofday (struct timeval *restrict tv, void *restrict tz)
  65 {
  66 #undef gettimeofday
  67 #ifdef WINDOWS_NATIVE
  68
  69   /* On native Windows, there are two ways to get the current time:
  70      GetSystemTimeAsFileTime
  71      <https://msdn.microsoft.com/en-us/library/ms724397.aspx>
  72      or
  73      GetSystemTimePreciseAsFileTime
  74      <https://msdn.microsoft.com/en-us/library/hh706895.aspx>.
  75      GetSystemTimeAsFileTime produces values that jump by increments of
  76      15.627 milliseconds (!) on average.
  77      Whereas GetSystemTimePreciseAsFileTime values usually jump by 1 or 2
  78      microseconds.
  79      More discussion on this topic:
  80      <http://www.windowstimestamp.com/description>.  */
  81   FILETIME current_time;
  82
  83   if (!initialized)
  84     initialize ();
  85   if (GetSystemTimePreciseAsFileTimeFunc != NULL)
  86     GetSystemTimePreciseAsFileTimeFunc (&current_time);
  87   else
  88     GetSystemTimeAsFileTime (&current_time);
  89
  90   /* Convert from FILETIME to 'struct timeval'.  */
  91   /* FILETIME: <https://msdn.microsoft.com/en-us/library/ms724284.aspx> */
  92   ULONGLONG since_1601 =
  93     ((ULONGLONG) current_time.dwHighDateTime << 32)
  94     | (ULONGLONG) current_time.dwLowDateTime;
  95   /* Between 1601-01-01 and 1970-01-01 there were 280 normal years and 89 leap
  96      years, in total 134774 days.  */
  97   ULONGLONG since_1970 =
  98     since_1601 - (ULONGLONG) 134774 * (ULONGLONG) 86400 * (ULONGLONG) 10000000;
  99   ULONGLONG microseconds_since_1970 = since_1970 / (ULONGLONG) 10;
 100   tv->tv_sec = microseconds_since_1970 / (ULONGLONG) 1000000;
 101   tv->tv_usec = microseconds_since_1970 % (ULONGLONG) 1000000;
 102
 103   return 0;
 104
 105 #else
 106
 107 # if HAVE_GETTIMEOFDAY
 108 #  if GETTIMEOFDAY_CLOBBERS_LOCALTIME
 109   /* Save and restore the contents of the buffer used for localtime's
 110      result around the call to gettimeofday.  */
 111   struct tm save = *localtime_buffer_addr;
 112 #  endif
 113
 114 #  if defined timeval /* 'struct timeval' overridden by gnulib?  */
 115 #   undef timeval
 116   struct timeval otv;
 117   int result = gettimeofday (&otv, (struct timezone *) tz);
 118   if (result == 0)
 119     {
 120       tv->tv_sec = otv.tv_sec;
 121       tv->tv_usec = otv.tv_usec;
 122     }
 123 #  else
 124   int result = gettimeofday (tv, (struct timezone *) tz);
 125 #  endif
 126
 127 #  if GETTIMEOFDAY_CLOBBERS_LOCALTIME
 128   *localtime_buffer_addr = save;
 129 #  endif
 130
 131   return result;
 132
 133 # else
 134
 135 #  if !defined OK_TO_USE_1S_CLOCK
 136 #   error "Only 1-second nominal clock resolution found.  Is that intended?" \
 137           "If so, compile with the -DOK_TO_USE_1S_CLOCK option."
 138 #  endif
 139   tv->tv_sec = time (NULL);
 140   tv->tv_usec = 0;
 141
 142   return 0;
 143
 144 # endif
 145 #endif
 146 }