Re: calculation of pi

[Mischa Baars <mjbaars1977 at gmail dot com>]

On 11/04/2012 02:45 AM, Ian Lance Taylor wrote:
> On Sat, Nov 3, 2012 at 12:55 AM, Mischa Baars <mjbaars1977@gmail.com> wrote:
> > On 11/02/2012 07:11 PM, Ian Lance Taylor wrote:
> > > On Fri, Nov 2, 2012 at 8:13 AM, Mischa Baars <mjbaars1977@gmail.com>
> > > wrote:
> > > > I have been writing this piece of example code, but it seems that someone
> > > > has been modifying the compiler in the meantime such that arguments are
> > > > now
> > > > passed in xmm registers instead of over the stack. Also the npx top of
> > > > stack
> > > > pointer isn't handled alike for all three different types of real numbers
> > > > on
> > > > function return any more.
> > > I have not looked at your code.  However, I can tell you that on
> > > 32-bit x86 floating point function arguments are normally passed on
> > > the stack and on 64-bit x86 floating point arguments are normally
> > > passed in the xmm registers.  There are various ways that you can
> > > change this default behaviour, but if you are seeing an unexpected
> > > change then I would guess that you changed from 32-bit compilation to
> > > 64-bit compilation.
> > >
> > > Ian
> >
> > By the way, it seems this only holds for single and double real numbers.
> > These are indeed passed in xmm registers, the long double however is still
> > passed over the stack.
> Yes.
>
> > Do we have any compiler options that change this behaviour back to the
> > original? The default behaviour in 64-bit mode is not even the same for all
> > real number types.
> There is no "original."  The 32-bit and 64-bit ABIs are different.
> The 64-bit ABI has always passed arguments in registers.  There is no
> option to force the 64-bit compiler to pass arguments on the stack.
>
> Ian

Sounds more logical to me, that a least all types of numbers are treated 
in the same manner. I suppose the ABI should be modified then if you ask me.

Mischa.