Re: [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h

Richard Henderson <[email protected]> Thu, 26 Jan 2006 00:06:18 +0000

Newsgroups	org.kernel.vger.ultralinux,org.kernel.vger.linux-ia64,org.kernel.vger.linux-kernel,org.kernel.vger.linux-mips,org.kernel.vger.sparclinux,org.ozlabs.lists.linuxppc-dev
Message-ID	<[email protected]>

On Wed, Jan 25, 2006 at 08:02:50PM +0000, Russell King wrote:
> > +	s = 16; if (word << 16 != 0) s = 0; b += s; word >>= s;
> > +	s =  8; if (word << 24 != 0) s = 0; b += s; word >>= s;
> > +	s =  4; if (word << 28 != 0) s = 0; b += s; word >>= s;
...
> Basically, shifts which depend on a variable are more expensive than
> constant-based shifts.

Actually, they're all constant shifts.  Just written stupidly.


r~