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Re: State of m68k float emulation in lb1sf68.asm (muldf, divdf)
- From: <tm_gccmail at kloo dot net>
- To: Pavel Pisa <pisa at cmp dot felk dot cvut dot cz>
- Cc: gcc at gcc dot gnu dot org
- Date: Fri, 14 Nov 2003 11:34:51 -0800 (PST)
- Subject: Re: State of m68k float emulation in lb1sf68.asm (muldf, divdf)
On Fri, 14 Nov 2003, Pavel Pisa wrote:
> Hello everybody,
>
> 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.
>
> Kazu Hirata sugests to start discussion about this case
> on GCC list.
>
> The core part of muldf implementation can be rewritten to use
> something like (not fully evaluated) u64*u64->u128, this can be realized
> by four u32*u32->u64.
I believe you only need three.
The result of the fourth multiply will be shifted left 64, which means
it will not be used.
Toshi