left operand
right operand
set if an overflow occurs, is not affected otherwise
the difference
bool overflow; assert(subs(2, -3, overflow) == 5); assert(!overflow); assert(subs(1, -int.max + 1, overflow) == int.max); assert(!overflow); assert(subs(int.min + 1, 1, overflow) == int.min); assert(!overflow); assert(subs(int.max, -1, overflow) == int.min); assert(overflow); overflow = false; assert(subs(int.min, 1, overflow) == int.max); assert(overflow); assert(subs(0, 0, overflow) == 0); assert(overflow); // sticky
bool overflow; assert(subs(2L, -3L, overflow) == 5); assert(!overflow); assert(subs(1L, -long.max + 1, overflow) == long.max); assert(!overflow); assert(subs(long.min + 1, 1, overflow) == long.min); assert(!overflow); assert(subs(-1L, long.min, overflow) == long.max); assert(!overflow); assert(subs(long.max, -1, overflow) == long.min); assert(overflow); overflow = false; assert(subs(long.min, 1, overflow) == long.max); assert(overflow); assert(subs(0L, 0L, overflow) == 0); assert(overflow); // sticky
Subtract two signed integers, checking for overflow.
The overflow is sticky, meaning a sequence of operations can be done and overflow need only be checked at the end.