Java like function getLeastSignificantBits() & getMostSignificantBits in Python?

问题

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

回答1:

efe640fc5d2f0036 in decimal is 17286575672347525174. Substract 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

EDIT: 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)

回答2:

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"

来源：https://stackoverflow.com/questions/40140892/java-like-function-getleastsignificantbits-getmostsignificantbits-in-python

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