Because integers and longs are never really distinguished in the ILP32 data-type model, your existing code probably uses them indiscriminately. Modify any code that uses integers and longs interchangeably so it conforms to the requirements of both the ILP32 and LP64 data-type models. While an integer and a long are both 32-bits in the ILP32 data-type model, a long is 64 bits in the LP64 data-type model.
Consider the following example:
int waiting; long w_io; long w_swap; ... waiting = w_io + w_swap; % warning: assignment of 64-bit integer to 32-bit integer
Furthermore, large arrays of long or unsigned long can cause serious performance degradation in the LP64 data-type model as compared to arrays of int or unsigned int. Large arrays of long or unsigned long can also cause significantly more cache misses and consume more memory.
Therefore, if int works just as well as long for the application purposes, use int rather than long.
This argument also applies to using arrays of int instead of arrays of pointers. Some C applications suffer from serious performance degradation after conversion to the LP64 data-type model because they rely on many large arrays of pointers.