Dave Korn wrote:
On 22 December 2006 00:59, Denis Vlasenko wrote:
Or this, absolutely typical C code. i386 arch can compare
16 bits at a time here (luckily, no alighment worries on this arch):
Whaddaya mean, no alignment worries? Misaligned accesses *kill* your
performance!
is it really worse to do one unaligned 16-bit read, than two separate
8-bit reads? I am surprised ... and of course you have the gain from
shorter code, reducing i-cache pressure.
I know this doesn't affect correctness, but the coder might well have known
that the pointer is unaligned and written two separate byte-sized accesses on
purpose; volatile isn't the answer because it's too extreme, there's nothing
wrong with caching these values in registers and they don't spontaneously
change on us.
