Compression.cs

/* THANKS TO ERU FOR THE HPF COMPRESSION ALGORITHM! */

namespace Capricorn.IO.Compression;

/// <summary>
///     HPF Compression Algorithm Class
/// </summary>
public class HPFCompression
{
    /// <summary>
    ///     Decompresses a compressed HPF file.
    /// </summary>
    /// <param name="file">File to decompress.</param>
    /// <returns>Array of bytes containing the decompressed data.</returns>
    public static byte[] Decompress(string file)
    {
        // Random Variables
        uint k = 7;
        uint val = 0;
        uint val2 = 0;
        uint val3 = 0;
        uint i = 0;
        uint j = 0;
        uint l = 0;
        uint m = 0;

        // Read HPF File
        var hpfBytes = File.ReadAllBytes(file);
        var hpfSize = hpfBytes.Length;

        // Allocate Memory for Decoded Picture
        var rawBytes = new byte[hpfSize * 10];

        // Prepare Arrays
        var int_odd = new uint[256];
        var int_even = new uint[256];
        var byte_pair = new byte[513];

        for (i = 0; i < 256; i++)
        {
            int_odd[i] = 2 * i + 1;
            int_even[i] = 2 * i + 2;

            byte_pair[i * 2 + 1] = (byte) i;
            byte_pair[i * 2 + 2] = (byte) i;
        }

        #region HPF Decompression

        while (val != 0x100)
        {
            val = 0;
            while (val <= 0xFF)
            {
                if (k == 7)
                {
                    l++;
                    k = 0;
                }
                else
                {
                    k++;
                }

                if ((hpfBytes[4 + l - 1] & (1 << (int) k)) != 0)
                    val = int_even[val];
                else
                    val = int_odd[val];
            }

            val3 = val;
            val2 = byte_pair[val];

            while (val3 != 0 && val2 != 0)
            {
                i = byte_pair[val2];
                j = int_odd[i];

                if (j == val2)
                {
                    j = int_even[i];
                    int_even[i] = val3;
                }
                else
                {
                    int_odd[i] = val3;
                }

                if (int_odd[val2] == val3)
                    int_odd[val2] = j;
                else
                    int_even[val2] = j;

                byte_pair[val3] = (byte) i;
                byte_pair[j] = (byte) val2;
                val3 = i;
                val2 = byte_pair[val3];
            }

            val += 0xFFFFFF00;

            if (val != 0x100)
            {
                rawBytes[m] = (byte) val;
                m++;
            }
        }

        #endregion

        // Copy Data to Exact Array
        var finalData = new byte[m];
        Buffer.BlockCopy(rawBytes, 0, finalData, 0, (int) m);

        // Return Finalized Data
        return finalData;
    }

    /// <summary>
    ///     Decompresses a compressed HPF byte array.
    /// </summary>
    /// <param name="hpfBytes">Data to decompress.</param>
    /// <returns>Array of bytes containing the decompressed data.</returns>
    public static byte[] Decompress(byte[] hpfBytes)
    {
        // Random Variables
        uint k = 7;
        uint val = 0;
        uint val2 = 0;
        uint val3 = 0;
        uint i = 0;
        uint j = 0;
        uint l = 0;
        uint m = 0;

        // Read HPF File
        var hpfSize = hpfBytes.Length;

        // Allocate Memory for Decoded Picture
        var rawBytes = new byte[hpfSize * 10];

        // Prepare Arrays
        var int_odd = new uint[256];
        var int_even = new uint[256];
        var byte_pair = new byte[513];

        for (i = 0; i < 256; i++)
        {
            int_odd[i] = 2 * i + 1;
            int_even[i] = 2 * i + 2;

            byte_pair[i * 2 + 1] = (byte) i;
            byte_pair[i * 2 + 2] = (byte) i;
        }

        #region HPF Decompression

        while (val != 0x100)
        {
            val = 0;
            while (val <= 0xFF)
            {
                if (k == 7)
                {
                    l++;
                    k = 0;
                }
                else
                {
                    k++;
                }

                if ((hpfBytes[4 + l - 1] & (1 << (int) k)) != 0)
                    val = int_even[val];
                else
                    val = int_odd[val];
            }

            val3 = val;
            val2 = byte_pair[val];

            while (val3 != 0 && val2 != 0)
            {
                i = byte_pair[val2];
                j = int_odd[i];

                if (j == val2)
                {
                    j = int_even[i];
                    int_even[i] = val3;
                }
                else
                {
                    int_odd[i] = val3;
                }

                if (int_odd[val2] == val3)
                    int_odd[val2] = j;
                else
                    int_even[val2] = j;

                byte_pair[val3] = (byte) i;
                byte_pair[j] = (byte) val2;
                val3 = i;
                val2 = byte_pair[val3];
            }

            val += 0xFFFFFF00;

            if (val != 0x100)
            {
                rawBytes[m] = (byte) val;
                m++;
            }
        }

        #endregion

        // Copy Data to Exact Array
        var finalData = new byte[m];
        Buffer.BlockCopy(rawBytes, 0, finalData, 0, (int) m);

        // Return Finalized Data
        return finalData;
    }
}