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Date: Mon, 09 Jun 97 00:57:00 PDT
From: Viraj Bais <Viraj_Bais@ccm.fm.intel.com>
Message-ID: <Mon, 09 Jun 97 01:04:22 PDT_10@ccm.fm.intel.com>
To: mills@udel.edu
Subject: Re: Daylight Savings bug in 3-5.90 on NT

Dave,

FYI, the NT port of xntp requires a bug fix. Following is my post in the
newsgroup explaining the problem.

Regards,
Viraj Bais
<viraj_bais@ccm.fm.intel.com>

_______________________________________________________________________________



Greg Schueman wrote:
> 
> I have heard several reports of this problem.  I have not yet found the
> solution in the code base.  I'm not sure where in NTP the problem is being
> introduced. I am actively looking into it, but it might be a month as I only 
> have snippets of time available.
>
> -Greg

There is a bug in the NT _ftime() system call (actually in one of the
Win32 API's that the _ftime() calls, I forget which one but one can
find out by stepping the code through the debugger) that returns
incorrect values if your timezone is one that does not adjust for
daylight's savings. In the xntp3.5f version, we have made some
changes to the winnt_gettimeofday() routine in lib/machines.c
file to fix this bug. I have not looked at 3.5-90, it would need
something similar.

OLD CODE:

int
winnt_gettimeofday(tv)
        struct timeval *tv;
{
        struct _timeb timebuffer;

        _ftime(timebuffer);
        tv->tv_sec = (long)timebuffer.time;
        tv->tv_usec = (long) (1000 * timebuffer.millitm));
        return 0;
}

CORRECTED CODE:

// 100ns intervals between 1/1/1601 and 1/1/1970 as reported by
// SystemTimeToFileTime()
#define FILETIME_1970 0x019db1ded53e8000
const BYTE DWLEN = sizeof(DWORD) * 8; //number of bits in DWORD

int
winnt_gettimeofday(tv)
        struct timeval *tv;
{
        FILETIME ft;
        __int64 msec;

        GetSystemTimeAsFileTime(&ft); // 100ns intervals since 1/1/1601
        msec = (__int64)ft.dwHighDateTime << DWLEN | ft.dwLowDateTime;
        msec = (msec - FILETIME_1970) / 10;
        tv->tv_sec = (long) (msec / 1000000);
        tv->tv_usec = (long) (msec % 1000000);
        return 0;
}