C CRC Calculation method rewritten in Python

C CRC Calculation method rewritten in Python

Certainly! Here's an example of how you can rewrite a CRC (Cyclic Redundancy Check) calculation method from C to Python. CRC calculation typically involves using a specific polynomial and algorithm. We'll provide a basic example assuming a CRC-32 calculation:

C Version (Example)

Let's assume a simple CRC-32 calculation in C:

#include <stdio.h> #include <stdint.h> // CRC32 polynomial #define CRC32_POLYNOMIAL 0xEDB88320UL // Function to calculate CRC32 uint32_t calculate_crc32(const uint8_t *data, size_t length) { uint32_t crc = 0xFFFFFFFF; // Initial value for (size_t i = 0; i < length; i++) { crc ^= data[i]; // XOR with data byte for (int j = 0; j < 8; j++) { crc = (crc >> 1) ^ (CRC32_POLYNOMIAL & (-(crc & 1))); } } return ~crc; // Final XOR with 0xFFFFFFFF } int main() { uint8_t data[] = { 0x01, 0x02, 0x03, 0x04 }; // Example data size_t length = sizeof(data) / sizeof(data[0]); uint32_t crc32 = calculate_crc32(data, length); printf("CRC32: 0x%08X\n", crc32); return 0; }

Python Version

Here's how you can rewrite the above CRC-32 calculation in Python:

def calculate_crc32(data): CRC32_POLYNOMIAL = 0xEDB88320 crc = 0xFFFFFFFF # Initial value for byte in data: crc ^= byte for _ in range(8): crc = (crc >> 1) ^ (CRC32_POLYNOMIAL if crc & 1 else 0) return crc ^ 0xFFFFFFFF # Final XOR with 0xFFFFFFFF # Example usage data = [0x01, 0x02, 0x03, 0x04] # Example data crc32 = calculate_crc32(data) print(f"CRC32: 0x{crc32:08X}")

Explanation:

  • CRC32_POLYNOMIAL: Represents the polynomial used in CRC-32 calculation.
  • crc: Starts with 0xFFFFFFFF (the initial value) and is updated byte-by-byte.
  • Final XOR: After processing all bytes, crc is XORed with 0xFFFFFFFF to get the final CRC value.

Notes:

  • Ensure that the data in Python is represented as a list of integers (bytes in C).
  • Python doesn't have fixed-width integers, so it handles integer sizes dynamically.

This Python implementation mirrors the logic of the C version, but adjusts for Python's dynamic typing and lack of fixed-width integers. Adjust as necessary for your specific CRC polynomial and data format.

Examples

  1. CRC-32 Calculation in Python

    • Description: Implementing CRC-32 calculation method in Python, similar to the C language.
    • Code:
      import binascii def crc32(data): crc = binascii.crc32(data.encode()) return crc & 0xffffffff # Usage example data = "Hello, world!" crc_value = crc32(data) print(f"CRC-32 of '{data}': {crc_value}")

    This Python code calculates CRC-32 checksum for a given string data using binascii.crc32.

  2. CRC-16 Calculation in Python

    • Description: Implementing CRC-16 calculation method in Python, akin to its C counterpart.
    • Code:
      def crc16(data): crc = 0xFFFF poly = 0xA001 for byte in data: crc ^= (ord(byte) & 0xFF) for _ in range(8): if crc & 0x0001: crc = (crc >> 1) ^ poly else: crc >>= 1 return crc # Usage example data = "Hello, world!" crc_value = crc16(data) print(f"CRC-16 of '{data}': {crc_value}")

    This Python function computes CRC-16 checksum for a given string data using the specified polynomial 0xA001.

  3. CRC-8 Calculation in Python

    • Description: Writing a CRC-8 calculation method in Python similar to how it is done in C.
    • Code:
      def crc8(data): crc = 0 for byte in data: crc ^= byte for _ in range(8): if crc & 0x80: crc = (crc << 1) ^ 0x07 else: crc <<= 1 return crc & 0xFF # Usage example data = b"Hello, world!" crc_value = crc8(data) print(f"CRC-8 of '{data.decode()}': {crc_value}")

    This Python function calculates CRC-8 checksum for a byte string data using the polynomial 0x07.

  4. CRC-CCITT Calculation in Python

    • Description: Implementing CRC-CCITT calculation method in Python, resembling its C implementation.
    • Code:
      def crc_ccitt(data): crc = 0xFFFF poly = 0x1021 for byte in data: crc ^= (byte << 8) for _ in range(8): if crc & 0x8000: crc = (crc << 1) ^ poly else: crc <<= 1 return crc & 0xFFFF # Usage example data = b"Hello, world!" crc_value = crc_ccitt(data) print(f"CRC-CCITT of '{data.decode()}': {crc_value}")

    This Python function computes CRC-CCITT checksum for a byte string data using the polynomial 0x1021.

  5. CRC-32 Calculation with Custom Polynomial in Python

    • Description: Implementing CRC-32 calculation with a custom polynomial in Python, similar to C.
    • Code:
      def crc32_custom(data): crc = 0xFFFFFFFF poly = 0xEDB88320 for byte in data: crc ^= (byte & 0xFF) for _ in range(8): if crc & 0x1: crc = (crc >> 1) ^ poly else: crc >>= 1 return crc ^ 0xFFFFFFFF # Usage example data = "Hello, world!" crc_value = crc32_custom(data.encode()) print(f"CRC-32 (custom) of '{data}': {crc_value}")

    This Python function computes CRC-32 checksum with a custom polynomial 0xEDB88320 for a string data.

  6. CRC Calculation Using Table Lookup in Python

    • Description: Writing a CRC calculation method in Python using table lookup approach, akin to C.
    • Code:
      def crc_table(data): table = [ 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF ] crc = 0xFFFF for byte in data: crc = ((crc << 4) & 0xFFFF) ^ table[((crc >> 12) ^ (byte >> 4)) & 0x0F] crc = ((crc << 4) & 0xFFFF) ^ table[((crc >> 12) ^ (byte & 0x0F)) & 0x0F] return crc # Usage example data = b"Hello, world!" crc_value = crc_table(data) print(f"CRC (table lookup) of '{data.decode()}': {crc_value}")

    This Python function calculates CRC using a precomputed lookup table for efficiency, similar to C implementations.

  7. CRC-16 Calculation with Custom Polynomial in Python

    • Description: Implementing CRC-16 calculation with a custom polynomial in Python, similar to C.
    • Code:
      def crc16_custom(data): crc = 0xFFFF poly = 0x8005 for byte in data: crc ^= (byte << 8) for _ in range(8): if crc & 0x8000: crc = (crc << 1) ^ poly else: crc <<= 1 return crc & 0xFFFF # Usage example data = "Hello, world!" crc_value = crc16_custom(data.encode()) print(f"CRC-16 (custom) of '{data}': {crc_value}")

    This Python function computes CRC-16 checksum with a custom polynomial 0x8005 for a string data.

  8. CRC Calculation with Bitwise XOR in Python

    • Description: Writing a CRC calculation method in Python using bitwise XOR operations, similar to C.
    • Code:
      def crc_xor(data): crc = 0 for byte in data: crc ^= byte for _ in range(8): if crc & 0x01: crc = (crc >> 1) ^ 0x8408 else: crc >>= 1 return crc & 0xFFFF # Usage example data = b"Hello, world!" crc_value = crc_xor(data) print(f"CRC (XOR) of '{data.decode()}': {crc_value}")

    This Python function calculates CRC using bitwise XOR operations, following a specific polynomial 0x8408.

  9. CRC-32 Calculation Using Python zlib Library

    • Description: Calculating CRC-32 checksum using Python's zlib library, similar to C.
    • Code:
      import zlib def crc32_zlib(data): crc = zlib.crc32(data.encode()) return crc & 0xFFFFFFFF # Usage example data = "Hello, world!" crc_value = crc32_zlib(data) print(f"CRC-32 (zlib) of '{data}': {crc_value}")

    This Python code uses zlib.crc32 to compute CRC-32 checksum for a string data.

  10. CRC-32 Calculation with Python bytearray

    • Description: Writing a CRC-32 calculation method in Python using bytearray, similar to C.
    • Code:
      def crc32_bytearray(data): crc = 0xFFFFFFFF poly = 0xEDB88320 data = bytearray(data.encode()) for byte in data: crc ^= byte for _ in range(8): if crc & 0x1: crc = (crc >> 1) ^ poly else: crc >>= 1 return crc ^ 0xFFFFFFFF # Usage example data = "Hello, world!" crc_value = crc32_bytearray(data) print(f"CRC-32 (bytearray) of '{data}': {crc_value}")

    This Python function computes CRC-32 checksum for a string data using bytearray and polynomial 0xEDB88320.

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