Re: print(268435456 + 1)

[Asko Kauppi <askok@...>]

One more reason for the int32 patch?

Honestly, is D3D changing the behaviour of doubles (non-integer),  
too, and is there a performance downside to using that safety flag to  
make D3d not jump on tables?

- asko

(sorry for being lazy and not googling this; but it's not my itch,  
just curious :)



Stefan Boberg kirjoitti 1.9.2006 kello 19.24:

>    Direct3D is probably changing the FPU mode to single-precision  
> under
> your feet. There's an initialization flag you can pass to D3D on
> creation which will avoid this.
>
> /Stefan
>
> > -----Original Message-----
> > From: lua-bounces@bazar2.conectiva.com.br [mailto:lua-
> > bounces@bazar2.conectiva.com.br] On Behalf Of Brian Weed
> > Sent: 01 September 2006 18:17
> > To: Lua list
> > Subject: Re: print(268435456 + 1)
> >
> > Brian Weed wrote:
> > > Aaron Brown wrote:
> > > > Brian Weed wrote:
> > > >
> > > > > Is there something about adding numbers that I should know
> > > > > about?
> > > >
> > > > > print(0x10000000)
> > > > > 268435456
> > > > >
> > > > > print(0x10000000 + 0x00000001)
> > > > > 268435456
> > > > >
> > > > > print(0x10000000 + 0x00000002)
> > > > > 268435456
> > > >
> > > > I get 268435456, 268435457, and 268435458.  My first guess
> > > > is that you're using (single-precision) floats instead of
> > > > doubles.  What platform are you on?  Did you change
> > > > LUA_NUMBER when compiling?
> > > >
> > > > http://docs.sun.com/source/806-3568/ncg_goldberg.html
> > > This is on Win32 (Lua is part of our game engine).  We did not
> modify
> > > LUA_NUMBER.  It's still double.
> > > Lua is compiled as a static lib via Visual C++ 6.0.  The app is
> > > compiled via Visual Studio 2005.
> > >
> > > Brian
> >
> > Ok, this is really weird...
> >
> > The following C code has the same problem (while watching "d" in the
> > debugger in Visual C++ 6.0):
> >
> > double d = 0x10000000;
> >
> > d = d + 0x00000002;
> >
> > doubles are supposed to be able to completely represent  a 32bit int
> > right?
> >
> > Brian