Re: [rfc] Add some more floatformat types ....

[Mark Kettenis <kettenis@wins.uva.nl>]

   Date: Fri, 17 Aug 2001 12:12:48 -0400
   From: Andrew Cagney <ac131313@cygnus.com>

   Ah, ok, now I understand.  So this means the original i386 did a 4:4:2 
   memory transfer when storing an extended float (long sigh)? The extra 2 
   bytes and the end of the `long double' always remaining undefined (long 
   double sigh)?  I've been hacking sane hardware for too long.

I think it shows here that the predecessor of the i386 was a 16-bit
processor.

   I think I'll clarify the `struct type . length' to:

   ``Length of storage for a value of this type. This is length of the type 
   and not the length of the value that resides within the type.  An 
   i386-ext floating-point value, for instance, only occupies 80 bits of 
   what is typically a 96 bit `long double'.''

Sounds good to me.  The key point here is that `struct type . length'
should match the debug info about the type.

   I'll drop the i387_ext from the list of things to add to floatformat.h.

I assume you mean that you'll leave it as it is now ;-).

   > I would simply introduce the builtin_type_i387_ext for the 80-bit
   > floating point type and keep builtin_type_long_double for the 96-bit
   > floating point type, both based on floatformat_i387_ext.
   > register_virtual_type would then indeed return builtin_type_i387_ext
   > for the floating-point registers.

   Ok.  The key thing here being that GDB gets two instead of one i387_ext 
   `struct type' (because the existing builtin_type_long_double can't 
   correctly describe an i387 register) which is really all I'm trying to 
   achieve.

Yep.

   --

    > The IA-64, for instance, has an 82 bit floating-point register.  That
    >    register is always represented in memory as 128 bits. 
   Consequently, my
    >    proposal includes ia64_ext128 and not ia64_ext82.
    >
    > So we only need a single floatformat_ia64_ext.  Why not keep the
    > floatformat_ia64_ext that we already have in ia64-tdep.c and move it
    > to ../libiberty/floatformat.c?

   Dam!  You spotted my cunning plan :-)  That is one of the next steps. 
   In the light of the exchange above, a double check on this one is in order.

Seems the ia64 stuff is even more braindamaged than the i386 stuff.

   Mark, this meaning that the ia64_ext should have a size of 128 and not 
   82 as it currently does in ia64-tdep.c?

I think so.  (But I also think we should rename it to ia64_reg as
Kevin proposes).

Mark