First, please read this function: tadd_ok.
/* Determine whether arguments can be subtracted without overflow */
int tsub_ok(int x, int y) {
return tadd_ok(x, -y);
}This code has bug, if x = 0x8000 0000, y = 0x8000 0000, then -y = 0x8000 0000 also, and the result is 0, and its overflow.