remainder = expr mod modulus
The mod operator subtracts from
abs(expr) the largest multiple of
abs(modulus) which is less than or equal to
abs(expr), and returns the result as remainder. If expr is negative, then a negative result is returned in remainder.
Note that if expr and modulus are both integers, the result of mod is just the remainder of the integer division operation expr / modulus.
Appendix D - Numeric Expressions