low and high are assumed to be positive and at most 2^31 - 1. So, there is a zeroed high bit in each which, for a signed int, is reserved to indicate negation.

low and high are assumed to be positive and at most 2^31 - 1. So, there is a zeroed high bit in each which, for a signed int, is reserved to indicate negation. When low and hi are summed together, the high bit of the result might be set. For a signed int, this would be an accidental overflow and would be falsely interpreted as a negative number. However, if you interpret the result as an unsigned int, it would be the correct sum. The Java logical shift operator >>> does not retain the sign when shifting. So, it will always shift a 0 into the high bit, making the result a positive signed int. In most C implementations, >> is an arithmetic shift, which would retain the sign in the result. So in C, we would need to cast low and high as unsigned first; otherwise, the high bit will be retained rather than shifted.