Christoph Mallon wrote:
Alexey Dokuchaev schrieb:
On Wed, Jan 14, 2009 at 07:05:27PM -0700, M. Warner Losh wrote:
In message: <20090115020752.52566769.s...@freebsd.org>
Stanislav Sedov <s...@freebsd.org> writes:
: > + shift = 8 * (reg & 3);
: > : : Would it make sense to replace this with
: > + shift = (reg & 3) << 3;
: : to not rely on possible compiler optimizations?
I don't think that it matters all that much these days...
But the name "shift" kinda suggests << instead of *, no?
The value *is* a shift amount (see its uses a few lines down). Its name
does not imply the way it is calculated, but what it is used for.
BTW: Even the most cheap compilers emit shift instructions for
multiplication by a power of two. The new code also is clearly faster
then the old - quite some code gets generated for switches.
I believe Warner's point is that the code is not in the hot path, so
that it should not really matter either way.
-Maxim
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