or download this
#!/usr/bin/perl -w
use strict;
use Benchmark;
...
Benchmark: running emptylist, xop, each for at least 5 CPU seconds...
emptylist: 5 wallclock secs ( 5.28 usr + 0.01 sys = 5.29 CPU) @ 22
+.12/s (n=117)
xop: 6 wallclock secs ( 5.50 usr + 0.02 sys = 5.52 CPU) @ 15
+.40/s (n=85)