CODEWITHSUNDEEP
pythonbitmapbit
rishabh
rishabh

Reputation: 1165

Java like function getLeastSignificantBits() & getMostSignificantBits in Python?

Can someone please help me out in forming an easy function to extract the leastSignificant & mostSignificant bits in Python?

Ex code in Java:

UUID u = UUID.fromString('a316b044-0157-1000-efe6-40fc5d2f0036');
long leastSignificantBits = u.getLeastSignificantBits();

private UUID(byte[] data) {
    long msb = 0;
    long lsb = 0;
    assert data.length == 16 : "data must be 16 bytes in length";
    for (int i=0; i<8; i++)
        msb = (msb << 8) | (data[i] & 0xff);
    for (int i=8; i<16; i++)
        lsb = (lsb << 8) | (data[i] & 0xff);
    this.mostSigBits = msb;
    this.leastSigBits = lsb;
}

--> Output value: -1160168401362026442

Upvotes: 3

Views: 2182

Answers (3)

Judee
Judee

Reputation: 1

FYI- In the case that you want to convert from Sigbits to UUID.

def sigbit2uuid(msb,lsb): 
    x = msb
    if x <= 0x7FFFFFFFFFFFFFFF:
        x += 0x10000000000000000
    msb_s=format(x,'x')
    msb_sl=[msb_s[:8],msb_s[8:12],msb_s[-4:]]
    msb_r='-'.join(msb_sl)

    y = lsb
    if y <= 0x7FFFFFFFFFFFFFFF:
        y += 0x10000000000000000
    lsb_s=format(y,'x')
    lsb_sl=[lsb_s[:4],lsb_s[-12:]]
    lsb_r='-'.join(lsb_sl)

    uuid=msb_r+'-'+lsb_r

    return uuid

Upvotes: 0

Jean-Fran&#231;ois Fabre
Jean-Fran&#231;ois Fabre

Reputation: 140168

efe640fc5d2f0036 in decimal is 17286575672347525174. Subtract 0x10000000000000000 from it & negate: you get -1160168401362026442

int("efe640fc5d2f0036",16)-0x10000000000000000 -> -1160168401362026442

Note that it's only guesswork but seems to work with the sole test case you provided (fortunately it was negative). Call that reverse engineering.

Take 2 last hex values (dash separated) and join them. I suppose the storage means that it becomes negative when first digit is above 7, so negate it with higher 2-power if that's the case:

def getLeastSignificantBits(s):
    hv = "".join(s.split("-")[-2:])
    v = int(hv,16)
    if int(hv[0],16)>7:
        # negative
        v = v-0x10000000000000000
    return v

print(getLeastSignificantBits('a316b044-0157-1000-efe6-40fc5d2f0036'))

result:

-1160168401362026442

Providing a method which takes the whole string and returns lsb & msb couple

def getLeastMostSignificantBits(s):
    sp=s.split("-")
    lsb_s = "".join(sp[-2:])
    lsb = int(lsb_s,16)
    if int(lsb_s[0],16)>7:
        # negative
        lsb = lsb-0x10000000000000000

    msb_s = "".join(sp[:3])
    msb = int(msb_s,16)
    if int(msb_s[0],16)>7:
        # negative
        msb = msb-0x10000000000000000

    return lsb,msb

print(getLeastMostSignificantBits('a316b044-0157-1000-efe6-40fc5d2f0036'))

result:

(-1160168401362026442, -6694969989912915968)

Upvotes: 3

Mattias Nilsson
Mattias Nilsson

Reputation: 3757

Old post but still... Just thought I'd add this:

import struct
import uuid

u = uuid.UUID('c88524da-d88f-11e9-9185-f85971a9ba7d')
msb, lsb = struct.unpack(">qq", u.bytes)

This give the values:
(-3997748571866721815, -7960683703264757123) ... and if I input those into the java.util.UUID constructor, it gives me back the uuid "c88524da-d88f-11e9-9185-f85971a9ba7d"

Upvotes: 6

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