Worms4Editor/LibXom/Data/XomCompressor.cs

using LibXom.Exceptions;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LibXom.Data
{
    public class XomCompressor
    {

        internal static int readCompressedIntFromStream(MemoryStream ms)
        {
            byte[] buffer = new byte[4];

            for (int i = 0; i < 4; i++)
            {
                int b = ms.ReadByte();
                buffer[i] = Convert.ToByte(b);
                if (b > 0x7F) continue;
                else break;
            }

            return DecompressInt(BitConverter.ToInt32(buffer));
        }
        public static int[] Decompress(byte[] input)
        {
            List<int> decompressedData = new List<int>();

            using (MemoryStream inputStream = new MemoryStream(input))
            {
                while (inputStream.Position < inputStream.Length)
                {
                    int n = readCompressedIntFromStream(inputStream);
                    decompressedData.Add(n);
                }

            }
            return decompressedData.ToArray();
        }
        private static int getNumberByteCount(int num)
        {
            uint unum = Convert.ToUInt32(num);
            if (unum <= 0xFF)       return 1;
            if (unum <= 0xFFFF)     return 2;
            if (unum <= 0xFFFFFF)   return 3;
            if (unum <= 0xFFFFFFFF) return 4;
            throw new XomException("Number is too large or too small.");
        }
        private static int decompressInt16(int compressedInt)
        {
            int mul = (compressedInt >> 8);
            int add = (compressedInt & 0xFF);

            return (mul * 0x80) + (add % 0x80);
        }
        private static int decompressInt24(int compressedInt)
        {
            int mul = (compressedInt >> 8) & 0xFF;
            int mul2 = (compressedInt >> 16);

            int add = (compressedInt & 0xFF);

            return ((mul2 * 0x80) * mul) + (add % 0x80);
        }

        private static int decompressInt32(int compressedInt)
        {
            int mul = (compressedInt >> 8) & 0xFF;
            int mul2 = (compressedInt >> 16) & 0xFF;
            int mul3 = (compressedInt >> 24);
             
            int add = (compressedInt & 0xFF);

            return (((mul3 * 0x80) * mul2 * 0x80) * mul * 0x80) + (add % 0x80);
        }

        public static int DecompressInt(int compressedInt)
        {
            switch (getNumberByteCount(compressedInt))
            {
                case 1:
                    return compressedInt;
                case 2:
                    return decompressInt16(compressedInt);
                case 3:
                    return decompressInt24(compressedInt);
                case 4:
                    return decompressInt32(compressedInt);
                default:
                    throw new XomException("Number is too large or too small.");
            }
        }
        public static int NextCompressedInterger(int compressedInt)
        {
            // Some parts of XOM follow a particular pattern,
            
            // 0x7b, 0x7d, 0x7e, 0x7f, 0x180
            // 0x1fb, 0x1fd, 0x1fe, 0x1ff 0x280 
            // 0x2fb, 0x2fd, 0x2fe, 0x2ff 0x380 

            // This function will take any given int,
            // and give you the next following this sequence.

            // This is done by XOM to "compress" intergers, 
            // you can read a int and, if its > 0x7f you know theres another byte to be read
            // otherwise you've read the entire interger, and can read the next one

            // add 1 to current int
            int nextId = compressedInt + 1;
            int byteCount = getNumberByteCount(nextId);

            // if its 0, just return 0
            if (nextId <= 0) return nextId;

            // if its a multiple of 0x80..
            if (nextId % 0x8000 == 0)
            {
                int div = nextId / 0x8000;
                // check if that divisor is also divisible by 2
                if (div % 0x2 == 0)
                    nextId += (0x8000); // add 0x8000
            }
            if (nextId % 0x80 == 0)
            {
                int div = nextId / 0x80;
                // check if that divisor is also divisible by 2
                if (div % 0x2 == 0)
                    nextId += (0x80); // add 0x80
            }

            byte[] buffer = BitConverter.GetBytes(nextId);
            for(int i = 0; i < 4; i++)
            {
                if (buffer[i] > 0x7F) continue;
                if (buffer[i] == 0) buffer[i]++;
                break;
            }
            nextId = BitConverter.ToInt32(buffer);

            return nextId;
        }
    }
}