How to get specific value from this function?

Question

I read this : https://stackoverflow.com/a/37605582/6426449

START_TIME = a constant that represents a unix timestamp

def make_id():

    t = int(time.time()*1000) - START_TIME
    u = random.SystemRandom().getrandbits(23)
    id = (t << 23 ) | u

    return id

def reverse_id(id):
    t  = id >> 23
    return t + START_TIME

From above def, How to get t and u of id(It's generated from def make_id)?

Like

def get_t(id):
    some methods
    return t

def get_u(id):
    some methods
    return u

@DanielRoseman Why can't you? It was created by shifting and ORing, you can undo it by shifting and masking. — Barmar, Sep 26 '17 at 08:23
Well, obviously you can write a function to do the opposite of what those do, but OP seems to want to access the actual variables inside the existing functions. — Daniel Roseman, Sep 26 '17 at 08:26
@DanielRoseman Where do you see that? The question says he wants to get them from the value of `id`. — Barmar, Sep 26 '17 at 17:01

score 1 · Accepted Answer · answered Sep 26 '17 at 08:17

1

To get t, just undo the left shift with a right shift.

def get_t(id):
    return id >> 23

To get u, use a bit mask with the rightmost 23 bits set

def get_u(id):
    return id & 0x7fffff

answered Sep 26 '17 at 08:17

Barmar

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How to get specific value from this function?

1 Answers1