Re: [Libreoffice] Mi first very little patch

On Mon, Sep 12, 2011 at 10:45:31PM +0200, CaStarCo wrote:

> @Lionel , What is the QuadPart member of the structure? The high
> part? the low part? or another thing?

The union is fully described at
http://msdn.microsoft.com/en-us/library/aa383713(v=vs.85).aspx

Are you familiar with the concept of C/C++ union? If not, Google gives
a few hits that don't seem too bad at first sight:

 http://www.cplusplus.com/doc/tutorial/other_data_types/#union
 http://www.go4expert.com/forums/showthread.php?t=15
 http://en.wikipedia.org/wiki/Union_(computer_science)
 http://msdn.microsoft.com/en-us/library/y9zewe0d(v=vs.80).aspx

To get to your question, the QuadPart is the whole 64 bits, that is
the combination of the high part *and* the low part.

Essentially, the paragraph I quoted says that to treat the FILETIME
value as a 64bit integer, one should proceed as such:

__int64     Value;
FILETIME *ft = // some value
ULARGE_INTEGER t;
t.LowPart = ft->dwLowDateTime;
t.HighPart = ft->dwHighDateTime;
// Now, t.QuadPart contains the right 64 bits integer
Value = t.QuadPart; // or use t.QuadPart directly instead of Value

instead of:

Value = *(__int64*)ft;


Do not hesitate to CC to me any additional question you have on this
matter.


> 2011/9/12 Lionel Elie Mamane <lionel@mamane.lu>

> > On Sun, Sep 11, 2011 at 10:04:52PM +0200, CaStarCo wrote:
> > > I've created a second (very little too) patch to reduce the scope of a
> > > variable.

> > > --- a/sal/osl/w32/file_dirvol.cxx
> > > +++ b/sal/osl/w32/file_dirvol.cxx
> > > @@ -60,7 +60,6 @@ extern "C" BOOL TimeValueToFileTime(const TimeValue *cpTimeVal, FILETIME 
> > > *pFTime

> > Thank you for your contribution to LibreOffice, it is most
> > welcome. Looking at that function in that file, it needs a more
> > thorough cleanup, and maybe other functions in that file and/or in
> > other files in the same directory; see
> > http://msdn.microsoft.com/en-us/library/ms724284%28v=VS.85%29.aspx, in
> > particular:

> >  It is not recommended that you add and subtract values from the
> >  FILETIME structure to obtain relative times. Instead, you should copy
> >  the low- and high-order parts of the file time to a ULARGE_INTEGER
> >  structure, perform 64-bit arithmetic on the QuadPart member, and copy
> >  the LowPart and HighPart members into the FILETIME structure.

> >  Do not cast a pointer to a FILETIME structure to either a
> >  ULARGE_INTEGER* or __int64* value because it can cause alignment
> >  faults on 64-bit Windows.

> > It would be best to look at every place that FILETIME is used in that
> > directory.

> > Just in case you want to volunteer for that cleanup :)

> > When you send a patch, could you please confirm the patch is licensed
> > under MPL1.1/LGPLv3+? To make things easier, you can do a one-time
> > blanket "all my patches" thing if you wish, sort of common to do that.

-- 
Lionel