Path: chuka.playstation.co.uk!tjs
From: tjs@cs.monash.edu.au (Toby Sargeant)
Newsgroups: scea.yaroze.programming.gnu_compiler
Subject: Re: Does this work with GCC?
Date: 29 Oct 1999 08:27:27 GMT
Organization: PlayStation Net Yaroze (SCEE)
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On Thu, 28 Oct 1999 12:23:55 -0400, Brian Weed <bweed@vipah.com> wrote:
>             n = *u.p16;  // Crashes when p16 is odd

MIPS assembler uses the lh(u) instruction to load half words. There is a
restriction that the address loaded from be even, unlike x86 processors.
The compiler _could_ generate code to test every load and perform the
extra work when the access was unaligned, but that would be rather ugly.
It's also possible to do this as an exception (i.e. trap the unaligned
load/store and do the rightThing(tm) in the exception handler). Both of
these are significant performance hits. Stick to using aligned pointers :)

Toby.