pub fn exp_reverse_bits_len_fast(
        &mut self,
        x: Felt<C::F>,
        power_bits: &Array<C, Var<C::N>>,
        bit_len: impl Into<Usize<C::N>>,
    ) -> Felt<C::F> {
        // Instantiate an array of length one and store the value of x.
        let mut x_copy_arr: Array<C, Felt<C::F>> = self.dyn_array(1);
        self.set(&mut x_copy_arr, 0, x);

        // Get a pointer to the address holding x.
        let x_copy_arr_ptr = match x_copy_arr {
            Array::Dyn(ptr, _) => ptr,
            _ => panic!("Expected a dynamic array"),
        };

        // Materialize the bit length as a Var.
        let bit_len_var = bit_len.into().materialize(self);
        // Get a pointer to the array of bits in the exponent.
        let ptr = match power_bits {
            Array::Dyn(ptr, _) => ptr,
            _ => panic!("Expected a dynamic array"),
        };

        // Call the DslIR instruction ExpReverseBitsLen, which modifies the memory pointed to by
        // `x_copy_arr_ptr`.
        self.push_op(DslIr::ExpReverseBitsLen(x_copy_arr_ptr, ptr.address, bit_len_var));

        // Return the value stored at the address pointed to by `x_copy_arr_ptr`.
        self.get(&x_copy_arr, 0)
    }
A version of `exp_reverse_bits_len` that uses the ExpReverseBitsLen precompile.
crates/recursion/compiler/src/ir/utils.rs