Re: State of m68k float emulation in lb1sf68.asm (muldf, divdf)

[Jim Wilson <wilson at specifixinc dot com>]

Pavel Pisa wrote:
> I have looked into lb1sf68.asm and I have found that implementation
> is very ineffective. It can be many times improved at least for CPU32
> targets I expect 6-20 times improvement.

FP emulation is a complicated business.  If you want to get into this 
area, you should do some reading on computer arithmetic if you already 
haven't.

If lb1sf68 is that bad, then why not just use fp-bit.c like most other 
targets do?  lb1sf68 has some fp exception stuff that fp-bit.c doesn't 
have, but if you don't need it, you are probably better off with fp-bit.c.

If you really want something better than fp-bit.c, then I would suggest 
looking into GMP.  You might need to do a m68k port of it.  I don't see 
any m68k code in the longlong.h file.  This helps with the portability, 
as you would define different longlong.h macros for different members of 
the m68k family.

Actually, now that I think about it, there was already a better fp-bit.c 
replacement offered by the GMP author, Torbjorn Granlund.  I suggest you 
look at this.
	http://gcc.gnu.org/ml/gcc/1999-07n/msg00553.html
I keep meaning to look at this, but haven't gotten around to it yet. 
Well, it has only been 4 years...

It shouldn't be necessary to have an m68k assembly language routine in 
order to get fast m68k FP emulation.
--
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com