Python .crc_hqx()

The .crc_hqx() function in Python’s built-in binascii module computes a 16-bit Cyclic Redundancy Check (CRC) value using the CRC-HQX algorithm, commonly used in the original Mac OS.

This checksum helps detect errors in data transmission or storage by verifying that the received data matches the original data.

Syntax

binascii.crc_hqx(data, value)

Parameters:

• data (bytes-like object): The binary data for which the CRC value is computed.
• value (integer): An optional 16-bit starting value for the checksum calculation. If omitted, the initial value is 0.

Return value:

Returns a 16-bit integer representing the computed CRC checksum of the input data, according to the CRC-HQX algorithm.

Example

In this example, the checksum is computed for a byte string, once with a non-zero starting value and once with an initial value of 0:

import binascii

data = b"Codecademy Docs"
initial_crc = 0xAAAA # A common non-zero starting value

# 1. Compute CRC with a starting value (0xAAAA)
crc_with_initial = binascii.crc_hqx(data, initial_crc)

# 2. Compute CRC starting from 0
crc_without_initial = binascii.crc_hqx(data, 0)

print(f"Data: {data!r}")
print(f"CRC (with initial value 0xAAAA): 0x{crc_with_initial:04x}")
print(f"CRC (starting from 0): 0x{crc_without_initial:04x}")

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The output of this code is:

Data: b'Codecademy Docs'
CRC (with initial value 0xAAAA): 0x134c
CRC (starting from 0): 0x67ce

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Codebyte Example

This example below computes the CRC-HQX checksum for a byte string using a starting value of 0:

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