Performing a bitwise NOT on arbitrarily long integers

Here’s the surprisingly simple solution to a fairly challenging problem. I do not understand why PHPs GMP extension does not include a gmp_not() function.

function gmp_not($n) {
	
	# convert to binary string
	$n = gmp_strval($n, 2);
	
	# invert each bit, one at a time
	for($i = 0; $i < strlen($n); $i++) {
		$n[$i] = ~$n[$i];
	}
	
	# convert back to decimal
	return gmp_strval(gmp_init($n, 2), 10);
}

Written on September 4, 2009