romrepomgr/RomRepoMgr.Core/Checksums/CRC32Context.cs

// /***************************************************************************
// Aaru Data Preservation Suite
// ----------------------------------------------------------------------------
//
// Filename       : CRC32Context.cs
// Author(s)      : Natalia Portillo <claunia@claunia.com>
//
// Component      : Checksums.
//
// --[ Description ] ----------------------------------------------------------
//
//     Implements a CRC32 algorithm.
//
// --[ License ] --------------------------------------------------------------
//
//     This library is free software; you can redistribute it and/or modify
//     it under the terms of the GNU Lesser General Public License as
//     published by the Free Software Foundation; either version 2.1 of the
//     License, or (at your option) any later version.
//
//     This library is distributed in the hope that it will be useful, but
//     WITHOUT ANY WARRANTY; without even the implied warranty of
//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
//     Lesser General Public License for more details.
//
//     You should have received a copy of the GNU Lesser General Public
//     License along with this library; if not, see <http://www.gnu.org/licenses/>.
//
// ----------------------------------------------------------------------------
// Copyright © 2011-2024 Natalia Portillo
// ****************************************************************************/

using System.IO;
using System.Text;
using Aaru.CommonTypes.Interfaces;
using Aaru.Helpers;

namespace Aaru.Checksums;

/// <summary>Implements a CRC32 algorithm</summary>
public sealed class Crc32Context : IChecksum
{
    const uint CRC32_ISO_POLY = 0xEDB88320;
    const uint CRC32_ISO_SEED = 0xFFFFFFFF;

    readonly uint   _finalSeed;
    readonly uint[] _table;
    uint            _hashInt;

    /// <summary>Initializes the CRC32 table and seed as CRC32-ISO</summary>
    public Crc32Context()
    {
        _hashInt   = CRC32_ISO_SEED;
        _finalSeed = CRC32_ISO_SEED;

        _table = new uint[256];

        for(var i = 0; i < 256; i++)
        {
            var entry = (uint)i;

            for(var j = 0; j < 8; j++)
            {
                if((entry & 1) == 1)
                    entry = entry >> 1 ^ CRC32_ISO_POLY;
                else
                    entry >>= 1;
            }

            _table[i] = entry;
        }
    }

    /// <summary>Initializes the CRC32 table with a custom polynomial and seed</summary>
    public Crc32Context(uint polynomial, uint seed)
    {
        _hashInt   = seed;
        _finalSeed = seed;

        _table = new uint[256];

        for(var i = 0; i < 256; i++)
        {
            var entry = (uint)i;

            for(var j = 0; j < 8; j++)
            {
                if((entry & 1) == 1)
                    entry = entry >> 1 ^ polynomial;
                else
                    entry >>= 1;
            }

            _table[i] = entry;
        }
    }

    /// <inheritdoc />
    /// <summary>Updates the hash with data.</summary>
    /// <param name="data">Data buffer.</param>
    /// <param name="len">Length of buffer to hash.</param>
    public void Update(byte[] data, uint len)
    {
        for(var i = 0; i < len; i++) _hashInt = _hashInt >> 8 ^ _table[data[i] ^ _hashInt & 0xff];
    }

    /// <inheritdoc />
    /// <summary>Updates the hash with data.</summary>
    /// <param name="data">Data buffer.</param>
    public void Update(byte[] data) => Update(data, (uint)data.Length);

    /// <inheritdoc />
    /// <summary>Returns a byte array of the hash value.</summary>
    public byte[] Final() => BigEndianBitConverter.GetBytes(_hashInt ^ _finalSeed);

    /// <inheritdoc />
    /// <summary>Returns a hexadecimal representation of the hash value.</summary>
    public string End()
    {
        var crc32Output = new StringBuilder();

        for(var i = 0; i < BigEndianBitConverter.GetBytes(_hashInt ^ _finalSeed).Length; i++)
            crc32Output.Append(BigEndianBitConverter.GetBytes(_hashInt ^ _finalSeed)[i].ToString("x2"));

        return crc32Output.ToString();
    }

    /// <summary>Gets the hash of a file</summary>
    /// <param name="filename">File path.</param>
    public static byte[] File(string filename)
    {
        File(filename, out byte[] hash);

        return hash;
    }

    /// <summary>Gets the hash of a file in hexadecimal and as a byte array.</summary>
    /// <param name="filename">File path.</param>
    /// <param name="hash">Byte array of the hash value.</param>
    public static string File(string filename, out byte[] hash) =>
        File(filename, out hash, CRC32_ISO_POLY, CRC32_ISO_SEED);

    /// <summary>Gets the hash of a file in hexadecimal and as a byte array.</summary>
    /// <param name="filename">File path.</param>
    /// <param name="hash">Byte array of the hash value.</param>
    /// <param name="polynomial">CRC polynomial</param>
    /// <param name="seed">CRC seed</param>
    public static string File(string filename, out byte[] hash, uint polynomial, uint seed)
    {
        var fileStream = new FileStream(filename, FileMode.Open, FileAccess.Read);

        uint localhashInt = seed;

        var localTable = new uint[256];

        for(var i = 0; i < 256; i++)
        {
            var entry = (uint)i;

            for(var j = 0; j < 8; j++)
            {
                if((entry & 1) == 1)
                    entry = entry >> 1 ^ polynomial;
                else
                    entry >>= 1;
            }

            localTable[i] = entry;
        }

        for(var i = 0; i < fileStream.Length; i++)
            localhashInt = localhashInt >> 8 ^ localTable[fileStream.ReadByte() ^ localhashInt & 0xff];

        localhashInt ^= seed;
        hash         =  BigEndianBitConverter.GetBytes(localhashInt);

        var crc32Output = new StringBuilder();

        foreach(byte h in hash) crc32Output.Append(h.ToString("x2"));

        fileStream.Close();

        return crc32Output.ToString();
    }

    /// <summary>Gets the hash of the specified data buffer.</summary>
    /// <param name="data">Data buffer.</param>
    /// <param name="len">Length of the data buffer to hash.</param>
    /// <param name="hash">Byte array of the hash value.</param>
    public static string Data(byte[] data, uint len, out byte[] hash) =>
        Data(data, len, out hash, CRC32_ISO_POLY, CRC32_ISO_SEED);

    /// <summary>Gets the hash of the specified data buffer.</summary>
    /// <param name="data">Data buffer.</param>
    /// <param name="len">Length of the data buffer to hash.</param>
    /// <param name="hash">Byte array of the hash value.</param>
    /// <param name="polynomial">CRC polynomial</param>
    /// <param name="seed">CRC seed</param>
    public static string Data(byte[] data, uint len, out byte[] hash, uint polynomial, uint seed)
    {
        uint localhashInt = seed;

        var localTable = new uint[256];

        for(var i = 0; i < 256; i++)
        {
            var entry = (uint)i;

            for(var j = 0; j < 8; j++)
            {
                if((entry & 1) == 1)
                    entry = entry >> 1 ^ polynomial;
                else
                    entry >>= 1;
            }

            localTable[i] = entry;
        }

        for(var i = 0; i < len; i++) localhashInt = localhashInt >> 8 ^ localTable[data[i] ^ localhashInt & 0xff];

        localhashInt ^= seed;
        hash         =  BigEndianBitConverter.GetBytes(localhashInt);

        var crc32Output = new StringBuilder();

        foreach(byte h in hash) crc32Output.Append(h.ToString("x2"));

        return crc32Output.ToString();
    }

    /// <summary>Gets the hash of the specified data buffer.</summary>
    /// <param name="data">Data buffer.</param>
    /// <param name="hash">Byte array of the hash value.</param>
    public static string Data(byte[] data, out byte[] hash) => Data(data, (uint)data.Length, out hash);
}