modulo function
Modulo that handles negative (e.g. -1 % 7 → 6). Roadmap #129.
Implementation
int modulo(int value, int modulus) {
if (modulus <= 0) throw ArgumentError(_kErrModulusPositive, _kParamModulus);
final int r = value % modulus;
return r < 0 ? r + modulus : r;
}