How is -13 % 64 = -13 in PHP?

Derived from this question : (Java) How does java do modulus calculations with negative numbers?

Anywhere to force PHP to return positive 51?

update
Looking for a configuration setting to fix, instead hard-guessing

Or other math function like bcmath?

updated
Not entire convinced by that java answer, as it does not take account of negative modulus -13+(-64) =?

If GMP is available, you can use gmp_mod

Calculates n modulo d. The result is always non-negative, the sign of d is ignored.

Example:

echo gmp_strval(gmp_mod('-13', '64')); // 51

Note that n and d have to be GMP number resources or numeric strings. Anything else won't work¹

echo gmp_strval(gmp_mod(-13, 64));
echo gmp_mod(-13, 64);

will both return -51 instead (which is a bug).

¹ ^{running the above in this codepad, will produce 51 in all three cases. It won't do that on my development machine.}