Integer wraparound occurs when arithmetic exceeds a fixed-width integer’s range and the bit pattern cycles to the opposite boundary. Unsigned subtraction makes the behavior especially visible: subtracting one from zero produces the type’s maximum value. section 3.1.1
Use these implementation rules when choosing integer types and function parameters:
- Expect wraparound at integer limits, with unsigned values particularly vulnerable because zero is their lower boundary. section 3.1.1
- Do not use uint merely to signal that a function accepts positive values; converting a negative int can silently create a huge unsigned value. section 3.1.1
- Accept a signed value and validate it explicitly when negative input should be rejected, returning an error instead of relying on conversion. section 3.1.1
Unsigned subtraction
With var u uint64 initialized to zero, u = u - 1 yields 18446744073709551615. The value is large because the fixed-width representation rolls backward from zero to its maximum. section 3.1.1
Listing 3.3 Subtracting from an unsigned integer
var u uint64 // 0 u = u - 1 fmt.Println(u) // output: 18446744073709551615
Inspect the runnable subtraction example showing uint64 wraparound. section 3.1.1
