On 06/16/07 17:05, Alexander Staubo wrote:
On 6/16/07, Ron Johnson <ron.l.johnson@xxxxxxx> wrote:
> Hardware acceleration for quickly counting the number of
> set/unset/matching bits?
x86 doesn't already do that?
I don't think so. The fastest way, I believe, is to use precomputed
lookup tables. Same for finding the least/most significant set/unset
bit, and other operations useful for dealing with bit vectors.
A couple of new AMD Barcelona opcodes might help do that:
http://www.anandtech.com/showdoc.aspx?i=2939&p=6
While on the topic of instructions, AMD also introduced
a few new extensions to its ISA with Barcelona. There are
two new bit manipulation instructions: LZCNT and POPCNT.
Leading Zero Count (LZCNT) counts the number of leading
zeros in an op, while Pop Count counts the leading 1s in
an op. Both of these instructions are targeted at crypto-
graphy applications.
--
Ron Johnson, Jr.
Jefferson LA USA
Give a man a fish, and he eats for a day.
Hit him with a fish, and he goes away for good!
