Re: Coreaudio-api Digest, Vol 7, Issue 94
Re: Coreaudio-api Digest, Vol 7, Issue 94
- Subject: Re: Coreaudio-api Digest, Vol 7, Issue 94
- From: Ian Ollmann <email@hidden>
- Date: Mon, 15 Mar 2010 11:05:23 -0700
On Mar 15, 2010, at 10:49 AM, email@hidden wrote:
> Remember that the big thing which will cause exceptions on a PowerPC
> but not on an Intel is misaligned data fetches.
Actually, it is intel which will trigger the access exception on misaligned accesses. AltiVec just silently loads the vector from the address rounded down to a 16 byte aligned address, which is always safe, assuming the first byte in the vector is known to exist. You just might end up with data that you weren't expecting to get.
You can run into trouble on AltiVec though, since software strategies to deal with this alignment behavior typically load two vectors bracketing the misaligned vector, and shifting to get the part you want. If the address turns out to be aligned after all, you can crash because the second vector contains no valid data and might fall on a different (unmapped) page.
Ian _______________________________________________
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