Integer overflow

Decided

D-0063, settled by the language’s author: part of spec §18. Older text cites it as 18.63.

Wraps, in every build; never panics. Replaces §5.1’s proposal of a panic in debug. What every mainstream language but Rust and Swift does, and what hashing code relies on; signed overflow included, which C++ leaves undefined and Dazzle does not. The Integer methods say anything else (checked_add, saturating_sub) (§5.1)

Extended by D-0094 point 5 (r109): the rest of integer arithmetic is defined the same way. MIN / -1 wraps to MIN, MIN % -1 is 0, a shift count is taken modulo the width, and a negative value shifted left wraps. A division by zero, which has no answer to wrap to, panics (T-0129).