A separate variable isn't particularly necessary here, and given that the type
is unsigned, we only need to test the upper bound.
This also resolves two -Wtype-limits warnings
We can just initialize the array to be zeroed out. This is safer and less error-prone,
since the initializer is now associated with the variable directly, making it
impossible to put code relying on the zeroed out state before it (unlike with memset).
Mat M