Subject: Re: mpc8xx fpu emu

From: Conn Clark <[email-masked]>
Date: Wed, 11 Sep 2002 14:42:37 -0700

Hello Alban,

	Unfortunatly the ppc code generated by the -msoft-float option does not
pass values in the same way as code generated for a chip with a fpu or a kernel
with fpu emulation. This is done to get a boost in speed on fpuless chips. This
renders software/libraries compiled one way to not be compatible with stuff
compiled the other way when passing floating point values(Note: there are some
cases where they will work correctly together).

	The -msoft-float option does not increase executable/library size in
any signifigant way and provides a signifigant speed boost. Also a few people
say that the fpu emulation code in the kernel is buggy. The -msoft-float has
become the default way things are done on the fpuless Motorola 8xx family for
these reasons.

	This means you must compile everything (and I mean everything) to use
-msoft-float or compile everything to use the fpu. So if you are not interested
in building and maintaining your own tool chain and possibly squishing some fpu
emulation bugs, you are better off using -msoft-float like everybody else.

Hope this answers your question.

	Conn
--

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Conn Clark
Engineering Stooge				[email-masked]
Electronic Systems Technology Inc.		www.esteem.com

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