[fpc-devel] Re: Mac G3 and FPC

[Jonas Maebe]

On 18 nov 2004, at 14:01, Marco van de Voort wrote:

>> I think NetBSD and maybe some other obscure OSes are the only ones 
>> that
>> absolutely need this. Under Mac OS X, the performance loss of not 
>> using
>> -dppc603 will be minimal, because the RTL changes that this causes are
>> overridden by libc routines. The impact of the changes in the compiler
>> is much smaller.
>
> Ah, I thought it was FPU alignment?

It is. The compiler and RTL use FPU operations to copy data 8 bytes at 
a time (instead of 4 bytes at a time). You only get an exception on a 
603(e) if you try to load a double from (or store one to) an address 
which is not 4 byte aligned. Double variables are aligned on 4 byte 
boundaries by default by the compiler, so there is no problem there. 
Problems only occur for copy operations.


Jonas