gettimeofday.c 4.56 KB
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/* Provide gettimeofday for systems that don't have it or for which it's broken.

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   Copyright (C) 2001-2003, 2005-2007, 2009-2019 Free Software
   Foundation, Inc.
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   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
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   along with this program; if not, see <https://www.gnu.org/licenses/>.  */
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/* written by Jim Meyering */

#include <config.h>

/* Specification.  */
#include <sys/time.h>

#include <time.h>

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#if defined _WIN32 && ! defined __CYGWIN__
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# define WINDOWS_NATIVE
# include <windows.h>
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#endif

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#include "localtime-buffer.h"
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#ifdef WINDOWS_NATIVE

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/* Avoid warnings from gcc -Wcast-function-type.  */
# define GetProcAddress \
   (void *) GetProcAddress

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/* GetSystemTimePreciseAsFileTime was introduced only in Windows 8.  */
typedef void (WINAPI * GetSystemTimePreciseAsFileTimeFuncType) (FILETIME *lpTime);
static GetSystemTimePreciseAsFileTimeFuncType GetSystemTimePreciseAsFileTimeFunc = NULL;
static BOOL initialized = FALSE;

static void
initialize (void)
{
  HMODULE kernel32 = LoadLibrary ("kernel32.dll");
  if (kernel32 != NULL)
    {
      GetSystemTimePreciseAsFileTimeFunc =
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        (GetSystemTimePreciseAsFileTimeFuncType) GetProcAddress (kernel32, "GetSystemTimePreciseAsFileTime");
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    }
  initialized = TRUE;
}

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#endif

/* This is a wrapper for gettimeofday.  It is used only on systems
   that lack this function, or whose implementation of this function
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   causes problems.
   Work around the bug in some systems whereby gettimeofday clobbers
   the static buffer that localtime uses for its return value.  The
   gettimeofday function from Mac OS X 10.0.4 (i.e., Darwin 1.3.7) has
   this problem.  */
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int
gettimeofday (struct timeval *restrict tv, void *restrict tz)
{
#undef gettimeofday
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#ifdef WINDOWS_NATIVE
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  /* On native Windows, there are two ways to get the current time:
     GetSystemTimeAsFileTime
     <https://msdn.microsoft.com/en-us/library/ms724397.aspx>
     or
     GetSystemTimePreciseAsFileTime
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     <https://msdn.microsoft.com/en-us/library/hh706895.aspx>.
     GetSystemTimeAsFileTime produces values that jump by increments of
     15.627 milliseconds (!) on average.
     Whereas GetSystemTimePreciseAsFileTime values usually jump by 1 or 2
     microseconds.
     More discussion on this topic:
     <http://www.windowstimestamp.com/description>.  */
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  FILETIME current_time;

  if (!initialized)
    initialize ();
  if (GetSystemTimePreciseAsFileTimeFunc != NULL)
    GetSystemTimePreciseAsFileTimeFunc (&current_time);
  else
    GetSystemTimeAsFileTime (&current_time);

  /* Convert from FILETIME to 'struct timeval'.  */
  /* FILETIME: <https://msdn.microsoft.com/en-us/library/ms724284.aspx> */
  ULONGLONG since_1601 =
    ((ULONGLONG) current_time.dwHighDateTime << 32)
    | (ULONGLONG) current_time.dwLowDateTime;
  /* Between 1601-01-01 and 1970-01-01 there were 280 normal years and 89 leap
     years, in total 134774 days.  */
  ULONGLONG since_1970 =
    since_1601 - (ULONGLONG) 134774 * (ULONGLONG) 86400 * (ULONGLONG) 10000000;
  ULONGLONG microseconds_since_1970 = since_1970 / (ULONGLONG) 10;
  tv->tv_sec = microseconds_since_1970 / (ULONGLONG) 1000000;
  tv->tv_usec = microseconds_since_1970 % (ULONGLONG) 1000000;
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  return 0;

#else

# if HAVE_GETTIMEOFDAY
#  if GETTIMEOFDAY_CLOBBERS_LOCALTIME
  /* Save and restore the contents of the buffer used for localtime's
     result around the call to gettimeofday.  */
  struct tm save = *localtime_buffer_addr;
#  endif

#  if defined timeval /* 'struct timeval' overridden by gnulib?  */
#   undef timeval
  struct timeval otv;
  int result = gettimeofday (&otv, (struct timezone *) tz);
  if (result == 0)
    {
      tv->tv_sec = otv.tv_sec;
      tv->tv_usec = otv.tv_usec;
    }
#  else
  int result = gettimeofday (tv, (struct timezone *) tz);
#  endif

#  if GETTIMEOFDAY_CLOBBERS_LOCALTIME
  *localtime_buffer_addr = save;
#  endif

  return result;

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# else

#  if !defined OK_TO_USE_1S_CLOCK
#   error "Only 1-second nominal clock resolution found.  Is that intended?" \
          "If so, compile with the -DOK_TO_USE_1S_CLOCK option."
#  endif
  tv->tv_sec = time (NULL);
  tv->tv_usec = 0;

  return 0;

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# endif
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#endif
}