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pythondecimalcrccrc32
Marek
Marek

Reputation: 53

CRC - Python - How to calculate JAMCRC decimal number from string

I need to calculate CRC-32/JAMCRC decimal number from a string in Python 3. How can I do it? For example, this webpage does it: https://www.crccalc.com/ - for 'hello-world' it prints 1311505828. I would like to have script which does exactly the same calculation. I've already tried to use zlib.crc32 and binascii.crc32 but their results for 'hello-world' is 2983461467.

Upvotes: -1

Views: 1003

Answers (2)

Valentin C
Valentin C

Reputation: 1

This code snippet works for me. It calculates CRC32_JAMRC checksum of provided file:

import zlib

with open("some_file", "rb") as f:
    crc32_jamcrc = 0xffffffff - zlib.crc32(f.read())
    print(hex(crc32_jamcrc))

Upvotes: 0

Riccardo Bucco
Riccardo Bucco

Reputation: 15384

To compute the CRC-32/JAMCRC you can simply perform the bitwise-not of the standard CRC-32 (in your case, the CRC-32 of 'hello-world' is 2983461467). But you can't simply use the ~ operator, because it works with signed integers (see this answer). Instead, you first need a subtraction:

import zlib
x = b'hello-world'
crc32_jamcrc = int("0b"+"1"*32, 2) - zlib.crc32(x) # 1311505828

Upvotes: 1

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