$ time perl -e '$e = shift;sub inc{$c=shift; $c++;return $c;} $d=0; $d=inc($d) while $d < $e; print $d;' 1e3
1000
real    0m0.073s
user    0m0.030s
sys     0m0.030s

Laurent@Laurent-HP ~
$ time perl -e '$e = shift;sub inc{$c=shift; $c++;return $c;} $d=0; $d=inc($d) while $d < $e; print $d;' 1e4
10000
real    0m0.065s
user    0m0.046s
sys     0m0.015s

Laurent@Laurent-HP ~
$ time perl -e '$e = shift;sub inc{$c=shift; $c++;return $c;} $d=0; $d=inc($d) while $d < $e; print $d;' 1e5
100000
real    0m0.108s
user    0m0.046s
sys     0m0.046s

Laurent@Laurent-HP ~
$ time perl -e '$e = shift;sub inc{$c=shift; $c++;return $c;} $d=0; $d=inc($d) while $d < $e; print $d;' 1e6
1000000
real    0m0.496s
user    0m0.451s
sys     0m0.030s

Laurent@Laurent-HP ~
$ time perl -e '$e = shift;sub inc{$c=shift; $c++;return $c;} $d=0; $d=inc($d) while $d < $e; print $d;' 1e7
10000000
real    0m4.320s
user    0m4.274s
sys     0m0.030s