Re: new module 'isatty'

[Paolo Bonzini]

On 01/03/2012 09:36 AM, Eli Zaretskii wrote:
> > From: Bruno Haible<address@hidden>
> > Cc: bastien ROUCARIES<address@hidden>, Eli Zaretskii<address@hidden>, Eric 
> > Blake<address@hidden>, address@hidden, address@hidden
> > Date: Tue, 03 Jan 2012 03:56:56 +0100
> >
> > I'm adding this new module. Feel free to use it in 'grep'.
>
> Thanks
>
> > #define IsConsoleHandle(h) (((long) (h)&  3) == 3)
>
> Where does this magic come from, and can we be sure it will always
> hold?  If there's some documentation about this, I would suggest to
> mention it here.

http://lists.gnu.org/archive/html/bug-gnulib/2009-08/msg00065.html

It's documented in Wine's source code and in 
http://www.winehq.org/docs/winedev-guide/x3500:

Console handles, on the other hand, are not multiple of four, but have 
the two lower bit set (being a multiple of four means having the two 
lower bits reset). When KERNEL32 sees a handle with the two lower bits 
set, it then knows it's a console handle and takes appropriate 
decisions. For example, in the various kernel32!WaitFor*() functions, it 
transforms any console handle (input and output - strangely enough 
handles to console's screen buffers are waitable) into a dedicated wait 
event for the targetted console. There's an (undocumented) KERNEL32 
function GetConsoleInputWaitHandle() which returns the handle to this 
event in case you need it. Another interesting handling of those 
console's handles is in ReadFile() (resp. WriteFile()), which behavior, 
for console's handles, is transferred to ReadConsole() (resp. 
WriteConsole()). Note that's always the ANSI version of ReadConsole() / 
WriteConsole() which is called, hence using the default console's code 
page. There are some other spots affected, but you can look in 
dlls/kernel to find them all. All of this is implemented in Wine.

Paolo