pub fn bits2num_v_circuit(&mut self, bits: &[Var<C::N>]) -> Var<C::N> {
        let result: Var<_> = self.eval(C::N::zero());
        for i in 0..bits.len() {
            self.assign(result, result + bits[i] * C::N::from_canonical_u32(1 << i));
        }
        result
    }
Convert bits to a variable inside a circuit.
crates/recursion/compiler/src/ir/bits.rs