framinosona / crc-dot-net

.NET Standard library for calculating CRC checksums

Crc.NET

.NET Standard library for calculating any CRC checksums

Motivation

I recently wrote a C++ library crc.h, this is more or less a direct C# port of it, since our codebase consists of both C++ and C# it was useful to have a native C# implementation of it.

Usage

The main class is CrcBase, it implements System.Security.Cryptography.HashAlgorithm. There are child classes for popular bit lengths: Crc8Base, Crc16Base, Crc32Base

Configurable parameters are:

• Size The bit width of the CRC checksum
• Polynomial A polynomial to use for CRC computation
• InitialValue Initial value of the checksum
• FinalXorValue Value to XOR the rsult with after finishing computation
• ReflectInput Whether or not the input is reflected (bit order reversed)
• ReflectOutput Whether or not the result is reflected (bit order reversed)
• ExpectedCheck A checksum of an ASCII string "123456789". Used as a correctness check. Optional

By providing constructor parameters or deriving child classes, you can construct any CRC implementation. For example:

class Crc32 : Crc32Base
{
    public Crc32() : base(0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true, true)
    {
    }
}

The usage is then quite simple:

Crc32 crc = new Crc32();
byte[] bytes = Encoding.ASCII.GetBytes("abc123");
byte[] resultBytes = crc.ComputeHash(bytes);
uint resultNum = BitConverter.ToUInt32(resultBytes, 0);

The library uses a 256-length lookup table to compute 8 bits of the checksum at the same time for performance reasons. For reflected input, the table is reflected instead. Although more optimizations could be made for specific implementations with concrete parameters, the main goal was generality and customizability. Due to the lookup table however, it should be quite fast. As always - benchmark first, optimize only as needed.