I hope I have beaten syphilis to publishing GCC::Builtins

use GCC::Builtins qw/clz/; # or qw/:all/;
$msb1 = clz(10);
# 28
[download]

Disclaimer: Builtins are implemented by GCC, I am merely interfacing them to Perl with XS, mechanistically. All questions to GCC please.

bw, bliako