In this paper, we propose to exploit bitwise operations
to speed up some important computations such as looking
for a support of a value in a constraint, or determining
if a value is substitutable by another one. Considering
a computer equipped with an X-bit CPU, one can then expect
an increase of the performance by a coefficient up to X
(which may be important, since X is equal to 32 or 64 in
many current central units). To show the interest of
enforcing arc consistency using bitwise operations, we
introduce a new variant of AC3, denoted by AC3$^{bit}$,
which can be used when constraints are (or can be)
represented in extension. This new algorithm when embedded
in MAC, is approximately two times more efficient than
AC3$^{rm}$. Note that AC3$^{rm}$ is a variant of AC3 which
exploits the concept of residual supports and has been
shown to be faster than AC2001.