pub(crate) fn get_num_extra_ecall_cycles<AB: SP1AirBuilder>(
        &self,
        local: &SyscallInstrColumns<AB::Var>,
    ) -> AB::Expr {
        // The syscall code is the read-in value of op_a at the start of the instruction.
        let syscall_code = local.op_a_access.prev_value();

        let num_extra_cycles = syscall_code[2];

        // If `is_real = 0`, then the return value is `0` regardless of `num_extra_cycles`.
        // If `is_real = 1`, then the `op_a_access` will be done, and `num_extra_cycles` will be
        // correct.
        num_extra_cycles * local.is_real
    }
Returns the number of extra cycles from an ECALL instruction.
crates/core/machine/src/syscall/instructions/air.rs