On Tue, Apr 10, 2012 at 5:50 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> .. and you don't have a double shift, right? So you'd need to do two
> shifts and the or for each word.
Actually, if sparc has a "rotate" instruction, you can do with a
single shift (rotate) per word loop.
You need to set up a mask register based on the alignment, and
pre-load the first word, but if you do have a rotate you can rotate
and then use "and mask" first to generate the "high bits" of the
current word, and then use the "andn mask" to generate the low bits of
the next word. So then you just need a single rotate per loop, and
some (very minor) loop prep.
Of course, RISC people tended to throw out rotate too, so maybe you
don't have even that.
Linus
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