use ntheory 'forcomb'; sub Eily_LanX_vr { my ( $length, $ones ) = @_; my ( $str, $s, @r ); $str = '0' x $length; forcomb { $s = $str; substr $s, $_, 1, '1' for @_; push @r, $s; } $length, $ones; return \@r } cmpthese(-3, { Eily_LanX_vr => sub { Eily_LanX_vr(25, 5) }, Eily_LanX => sub { Eily_LanX(25, 5) }, }); __END__ Rate Eily_LanX Eily_LanX_vr Eily_LanX 11.9/s -- -59% Eily_LanX_vr 29.0/s 143% --