Re: Soft float for i486

[Michael Meissner <meissner@cygnus.com>]

Jeffrey A Law writes:
|   In message <199803140044.TAA22071@miacomet.wavemark.com>you write:
|   > 
|   > I'm trying to build a cross-compiler using egcs-980302, and I want to
|   > target a i486 chip that does NOT have floating point, and I don't want
|   > to emulate the instructions.
|   > 
|   > I've found the following fragment in gcc/config/a29k/t-a29kbare :
|   > 
|   > # These are really part of libgcc1, but this will cause them to be
|   > # built correctly, so... 
|   > 
|   > LIB2FUNCS_EXTRA = fp-bit.c dp-bit.c
|   > 
|   > dp-bit.c: $(srcdir)/config/fp-bit.c
|   > 	cat $(srcdir)/config/fp-bit.c > dp-bit.c
|   > 
|   > fp-bit.c: $(srcdir)/config/fp-bit.c
|   > 	echo '#define FLOAT' > fp-bit.c
|   > 	cat $(srcdir)/config/fp-bit.c >> fp-bit.c
|   > 
|   > 
|   > I'm just trying to figure a good place to put them (or should I just
|   > shove them in t-i386bare and be done with it)?
| Going over some of my old mail.  I never saw anyone respond to this.
| 
| 
| Yup.  That's the right place for them.

Actually, as it exists in egcs, config/fp-bit.c is not up to handling
the x86.  This is because config/fp-bit.c only handle 32 and 64 bit
floating point, and not the 80 bit fp that the x86 supports.  I know
that we've talked about doing this within Cygnus, but the changes are
not on the main branchline.

|   > Perhaps every target should have thos so -msoft-float will actually
|   > work for any target...
| It's a thought, at least for embedded targets, probably not worth it
| for native targets.
| 
| I'd be kind of suprised if more than a few embedded targets don't
| already handle the soft-float stuff.

You do get better fp performance if you are not trapping to the kernel 
(assuming you have a kernel) to do the emulation, but instead just
calling the routine directly.

| jeff