Too late for me to edit: as josefx pointed out, it also fails to properly address the undefined behavior. The sums INT_MAX + INT_MAX and INT_MIN + INT_MIN may still overflow despite being done using the long type.

That won't occur on an 'LP64' platform, [0] but we should aim for proper portability and conformance to the C language standard.

[0] https://en.wikipedia.org/wiki/64-bit_computing#64-bit_data_m...