How to use the reil.arm64.operand.get function in reil

def arm64_b(ctx, i):
    a = operand.get(ctx, i, 0)
    cond = conditional.condition(ctx, i.cc)
    ctx.emit(  jcc_  (cond, a))

def arm64_sub(ctx, i):
    if len(i.operands) == 3:
        dst_idx = 0
        a_idx = 1
        b_idx = 2
    else:
        dst_idx = 0
        a_idx = 0
        b_idx = 1

    a = operand.get(ctx, i, a_idx)
    b = operand.get(ctx, i, b_idx, a.size)

    result = ctx.tmp(a.size * 2)

    ctx.emit(  sub_  (a, b, result))

    if i.update_flags:
        _sub_set_flags(ctx, a, b, result)

    operand.set(ctx, i, dst_idx, result)

def arm64_sub(ctx, i):
    if len(i.operands) == 3:
        dst_idx = 0
        a_idx = 1
        b_idx = 2
    else:
        dst_idx = 0
        a_idx = 0
        b_idx = 1

    a = operand.get(ctx, i, a_idx)
    b = operand.get(ctx, i, b_idx, a.size)

    result = ctx.tmp(a.size * 2)

    ctx.emit(  sub_  (a, b, result))

    if i.update_flags:
        _sub_set_flags(ctx, a, b, result)

    operand.set(ctx, i, dst_idx, result)