s/iter   org   new  best
org    5.62    --  -78%  -94%
new    1.26  346%    --  -73%
best  0.345 1529%  266%    --
The results are the same

##</code><code>##

sub ba2bi2 {
	my @ba = reverse (@_, (0) x (4 - ( @_%4 || 4 ) ) );
	my $result = Math::BigInt->new(0);
	$result *= 4294967296
	, $result += $_
		for map{
				unpack 'N'
				, pack 'C4'
				, @ba[4*$_ .. 4*$_+3]
			} 0 .. ($#ba/4);
	return $result;
}