On Wed, Jan 25, 2006 at 04:06:18PM -0800, Richard Henderson wrote: > 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. Unfortunately that's not correct. You do not appear to have checked the compiler output like I did - this code does _not_ generate constant shifts. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core
