Macro pop_top

macro_rules! pop_top {
    ($interp:expr, $x1:ident) => { ... };
    ($interp:expr, $x1:ident, $x2:ident) => { ... };
    ($interp:expr, $x1:ident, $x2:ident, $x3:ident) => { ... };
}

Pops U256 values from the stack, and returns a reference to the top of the stack. Fails the instruction if the stack is too small.