Macro as_usize_or_fail_ret

macro_rules! as_usize_or_fail_ret {
    ($interp:expr, $v:expr, $ret:expr) => { ... };
    ($interp:expr, $v:expr, $reason:expr, $ret:expr) => { ... };
}

Converts a U256 value to a usize and returns ret, failing the instruction if the value is too large.