SaferIntegers

These integer types do not ignore arithmetic overflows and underflows.

A Safer Way

Using the default Int or UInt types allows overflow and underflow errors to occur silently, without notice. These incorrect values propagate and such errors are difficult to recognize after the fact.

This package exports safer versions. These types check for overflow and underflow in each of the basic arithmetic functions. The processing will stop with a message in the event of overflow or underflow. On one machine, the overhead relative to the built-in integer types is <= 1.2x.

Background

Integer overflow occurs when an integer type is increased beyond its maximum value. Integer underflow occurs when an integer type is decreased below its minimum value. Signed and Unsigned values are subject to overflow and underflow. With Julia, you can see the rollover using Int or UInt types:

typemax(Int) + one(Int) < 0
typemin(Int) - one(Int) > 0
typemax(UInt) + one(UInt) == typemin(UInt)
typemin(UInt) - one(UInt) == typemax(UInt)

There are security implications for integer overflow in certain situations.

a = Int16(456) * Int16(567)
# a == -3592

for i in 1:a
    secure(biohazard[i])
end

With a < 0, the for loop does not execute.