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, 2009-2019 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
  18
  19 /* written by Jim Meyering */
  20
  21 #include <config.h>
  22
  23 /* Specification.  */
  24 #include <sys/time.h>
  25
  26 #include <time.h>
  27
  28 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  29 # define WINDOWS_NATIVE
  30 # include <windows.h>
  31 #endif
  32
  33 #include "localtime-buffer.h"
  34
  35 #ifdef WINDOWS_NATIVE
  36
  37 /* GetSystemTimePreciseAsFileTime was introduced only in Windows 8.  */
  38 typedef void (WINAPI * GetSystemTimePreciseAsFileTimeFuncType) (FILETIME *lpTime);
  39 static GetSystemTimePreciseAsFileTimeFuncType GetSystemTimePreciseAsFileTimeFunc = NULL;
  40 static BOOL initialized = FALSE;
  41
  42 static void
  43 initialize (void)
  44 {
  45   HMODULE kernel32 = LoadLibrary ("kernel32.dll");
  46   if (kernel32 != NULL)
  47     {
  48       GetSystemTimePreciseAsFileTimeFunc =
  49         (GetSystemTimePreciseAsFileTimeFuncType) GetProcAddress (kernel32, "GetSystemTimePreciseAsFileTime");
  50     }
  51   initialized = TRUE;
  52 }
  53
  54 #endif
  55
  56 /* This is a wrapper for gettimeofday.  It is used only on systems
  57    that lack this function, or whose implementation of this function
  58    causes problems.
  59    Work around the bug in some systems whereby gettimeofday clobbers
  60    the static buffer that localtime uses for its return value.  The
  61    gettimeofday function from Mac OS X 10.0.4 (i.e., Darwin 1.3.7) has
  62    this problem.  */
  63
  64 int
  65 gettimeofday (struct timeval *restrict tv, void *restrict tz)
  66 {
  67 #undef gettimeofday
  68 #ifdef WINDOWS_NATIVE
  69
  70   /* On native Windows, there are two ways to get the current time:
  71      GetSystemTimeAsFileTime
  72      <https://msdn.microsoft.com/en-us/library/ms724397.aspx>
  73      or
  74      GetSystemTimePreciseAsFileTime
  75      <https://msdn.microsoft.com/en-us/library/hh706895.aspx>.
  76      GetSystemTimeAsFileTime produces values that jump by increments of
  77      15.627 milliseconds (!) on average.
  78      Whereas GetSystemTimePreciseAsFileTime values usually jump by 1 or 2
  79      microseconds.
  80      More discussion on this topic:
  81      <http://www.windowstimestamp.com/description>.  */
  82   FILETIME current_time;
  83
  84   if (!initialized)
  85     initialize ();
  86   if (GetSystemTimePreciseAsFileTimeFunc != NULL)
  87     GetSystemTimePreciseAsFileTimeFunc (&current_time);
  88   else
  89     GetSystemTimeAsFileTime (&current_time);
  90
  91   /* Convert from FILETIME to 'struct timeval'.  */
  92   /* FILETIME: <https://msdn.microsoft.com/en-us/library/ms724284.aspx> */
  93   ULONGLONG since_1601 =
  94     ((ULONGLONG) current_time.dwHighDateTime << 32)
  95     | (ULONGLONG) current_time.dwLowDateTime;
  96   /* Between 1601-01-01 and 1970-01-01 there were 280 normal years and 89 leap
  97      years, in total 134774 days.  */
  98   ULONGLONG since_1970 =
  99     since_1601 - (ULONGLONG) 134774 * (ULONGLONG) 86400 * (ULONGLONG) 10000000;
 100   ULONGLONG microseconds_since_1970 = since_1970 / (ULONGLONG) 10;
 101   tv->tv_sec = microseconds_since_1970 / (ULONGLONG) 1000000;
 102   tv->tv_usec = microseconds_since_1970 % (ULONGLONG) 1000000;
 103
 104   return 0;
 105
 106 #else
 107
 108 # if HAVE_GETTIMEOFDAY
 109 #  if GETTIMEOFDAY_CLOBBERS_LOCALTIME
 110   /* Save and restore the contents of the buffer used for localtime's
 111      result around the call to gettimeofday.  */
 112   struct tm save = *localtime_buffer_addr;
 113 #  endif
 114
 115 #  if defined timeval /* 'struct timeval' overridden by gnulib?  */
 116 #   undef timeval
 117   struct timeval otv;
 118   int result = gettimeofday (&otv, (struct timezone *) tz);
 119   if (result == 0)
 120     {
 121       tv->tv_sec = otv.tv_sec;
 122       tv->tv_usec = otv.tv_usec;
 123     }
 124 #  else
 125   int result = gettimeofday (tv, (struct timezone *) tz);
 126 #  endif
 127
 128 #  if GETTIMEOFDAY_CLOBBERS_LOCALTIME
 129   *localtime_buffer_addr = save;
 130 #  endif
 131
 132   return result;
 133
 134 # else
 135
 136 #  if !defined OK_TO_USE_1S_CLOCK
 137 #   error "Only 1-second nominal clock resolution found.  Is that intended?" \
 138           "If so, compile with the -DOK_TO_USE_1S_CLOCK option."
 139 #  endif
 140   tv->tv_sec = time (NULL);
 141   tv->tv_usec = 0;
 142
 143   return 0;
 144
 145 # endif
 146 #endif
 147 }