[Bug 2357] Speeding up render on Alpha with MVI instructions
Sun Jan 23 13:34:51 PST 2005
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------- Additional Comments From firstname.lastname@example.org 2005-01-23 13:34 -------
(In reply to comment #2)
> i386 does not "not care" about unaligned access. They don't generate traps, but
> they are much slower than aligned accesses. The code in
> fbCompositeSrcAdd_8888x8888mmx() assumes that the drawables are aligned on 4
> byte boundaries. Since the drawables are 32 bits per pixel, anything else would
> be insane.
> Are you seeing drawables that are aligned on a 16 bit boundary?
No. However, it happens frequently that src and dst aren't co-aligned, that is,
while (w && (unsigned long)dst & 7)
will make dst 8-byte-aligned, but (src % 8) == 4. Is it possible to somehow
ensure co-alignment? Otherwise, I would have to compensate for this in the
source (and that would probably also be helpful for i386, depending on how
slow unaligned accesses there really are...)
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