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Lupin_the_3rd
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Joined: 03 Apr 2005
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PostPosted: Fri Oct 12, 2007 1:03 am    Post subject: -mieee on alpha? Yes or no? Reply with quote

According to Gentoo Alpha porting guide, (here: http://www.gentoo.org/proj/en/base/alpha/doc/alpha-porting-guide.xml#doc_chap4 ) it says that on EV6 and better, the -mieee CFLAG is not required. It defines the flag as enabling "software assisted floating point at compile time". Since the EV6 and better processors have full IEEE floating point arithmetic implemented in hardware, it makes sense that the flag is not required.

Seemingly contradictory, over at the Gentoo Safe CFLAGS page, (here: http://gentoo-wiki.com/Safe_Cflags#Alpha_ev67 ) the EV67 example does include the -mieee flag! Wouldn't it be safer to omit an unnecessary CFLAG?

So the purpose of this post is two fold:

1: Is there any benefit to using (or not using) the -mieee flag on EV6 processors? Or does it generate the exact same code either way (on EV6)?

2: How many of you have EV6 (or better) and ARE using the -mieee flag? And why?
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desultory
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PostPosted: Fri Oct 12, 2007 7:04 am    Post subject: Reply with quote

It is enabled by default.
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sae
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Joined: 09 Apr 2005
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PostPosted: Sun Oct 21, 2007 6:51 pm    Post subject: Reply with quote

In the case of EV6, it has to do with it flushing denormalized numbers to zero... In some cases it is OK, but in others not, you will have to look into this yourself, I am not a numerical computation guru... :-)
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