Re: [PATCH 3/6] C-language equivalents of include/asm-*/bitops.h
Richard Henderson <[email protected]>
| Newsgroups | gmane.linux.ports.mips.general,gmane.linux.kernel,gmane.linux.ports.ia64,gmane.linux.ports.hppa,gmane.linux.ports.ppc.devel,gmane.linux.ports.sh.devel,gmane.linux.ports.sparc,gmane.linux.ports.ultrapenguin |
|---|---|
| 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~