Overflow checking for unary operators

[robinsierra]

Version Information

• Vyper version: 0.1.0b13+commit.6385900

What's your issue about?

The unary negation operator does not check for overflows:

@public
def neg(i: int128) -> int128:
    return -i

This is OK for all inputs except -2^127, for which it returns -2^127 instead of reverting.

[fubuloubu]

Good catch!

[robinsierra]

Overflows also happen for uint256, although it is questionable whether using negation on an unsigned value should be allowed at all.

[fubuloubu]

should not be allowed, yes