Date: Thu, 11 Jun 2015 10:59:01 -0400 From: Richard Yao <ryao@gentoo.org> To: Ian Lepore <ian@freebsd.org> Cc: Erich Dollansky <erichsfreebsdlist@alogt.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@FreeBSD.org> Subject: Re: allow ffs & co. a binary search Message-ID: <5579A235.80609@gentoo.org> In-Reply-To: <1434034373.1415.3.camel@freebsd.org> References: <20150607081315.7c0f09fb@B85M-HD3-0.alogt.com> <5579A016.4040800@gentoo.org> <1434034373.1415.3.camel@freebsd.org>
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[-- Attachment #1 --] On 06/11/2015 10:52 AM, Ian Lepore wrote: > On Thu, 2015-06-11 at 10:49 -0400, Richard Yao wrote: >> On 06/06/2015 08:13 PM, Erich Dollansky wrote: > [...] >> >> The fastest portable way of calculating highest bit set is to use a >> debrujin sequence: >> >> https://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn >> >> The binary approach is inferior, especially on Pentium 4 processors. > > And of course it's crucial that we optimize for Pentium 4 processors in > 2015. The debrujin approach is fast regardless of the architecture. Anyway, this is a solved problem. There is no need to reinvent the wheel when the portable solutions are listed on that page at Stanford. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBAgAGBQJVeaI6AAoJECDuEZm+6Exk9AgQAJfN9OjSLJyOQF+HSRWfjXRw Nz3eX1Hn83PrjvJUUFBxDFqTQQYycjgAAk/vbqCuy/hflRakdlAclXuP+ZiW6y5C eMo9sV8LtaBFqZ45ACrRCFno/gSEq/OWgSa7/EhBiRHBfu0k0x8xJbZMdT1ZPzQM yGG4+DIBQtXj42KzKjYIXs3QRepff3qMXAi/78ksmd5PZ7jNa1x1LTe+qZJP4hUC OJ/2XR6VRD/fLXGzfxgAjZS9Y1f2mno1oxPm91CntnpLPAyBVR/CWCBeCUADcM0E nycezA5h0pUU/53ayWe+TUc9dmKEBQ4SKXdi1PBGK4mBzoDvesQDV9aEq8ujTR3x eHxAOA897No5MrpFBCbE5MwDLYcZFoWY9owBYIuHXCIKBFfXr+GXu7pY6dGIvEKg p8GUk84Y+cvHLSzXbZHJru8YCKUBLsgUMZCKwLMHqeTCLa3oW455hFjombtvVwJ7 FuQV10+BZ8exI14SeyyZfrQJnPeLhS//HWobYq6AL9xLDVmXVf9qP3+U6g8eisyo xHBOL6ZhEHHyIiLISJL4YYAyZzk3Sr843FuEfIr+j6dqO6wlBmuWY3NlsiL3lotN Mb3lorTn4j4LOth3R8C/S5rfWgqpYUXzN77rGUunXcQU4u3Q6fxLp4HpQyK8+CdG /xZwTAbNIawevTIUViey =oPoC -----END PGP SIGNATURE-----
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