sharpcompress/SharpCompress/Compressor/PPMd/H/RangeCoder.cs

using System.Text;
using System.IO;
using SharpCompress.Compressor.Rar;

namespace SharpCompress.Compressor.PPMd.H
{
    internal class RangeCoder
    {
        internal const int TOP = 1 << 24;
        internal const int BOT = 1 << 15;
        internal const long UintMask = 0xFFFFffffL;

        // uint low, code, range;
        private long low, code, range;
        private Unpack unpackRead;
        private Stream stream;

        internal RangeCoder(Unpack unpackRead)
        {
            this.unpackRead = unpackRead;
            Init();
        }

        internal RangeCoder(Stream stream)
        {
            this.stream = stream;
            Init();
        }

        private void Init()
        {
            this.SubRange = new SubRange();

            low = code = 0L;
            range = 0xFFFFffffL;
            for (int i = 0; i < 4; i++)
            {
                code = ((code << 8) | Char) & UintMask;
            }
        }

        internal int CurrentCount
        {
            get
            {
                range = (range/SubRange.Scale) & UintMask;
                return (int) ((code - low)/(range));
            }
        }

        private long Char
        {
            get
            {
                if (unpackRead != null)
                    return (unpackRead.Char);
                if (stream != null)
                    return stream.ReadByte();
                return -1;
            }
        }

        internal SubRange SubRange { get; private set; }


        internal long GetCurrentShiftCount(int SHIFT)
        {
            range = Utility.URShift(range, SHIFT);
            return ((code - low)/(range)) & UintMask;
        }

        internal void Decode()
        {
            low = (low + (range*SubRange.LowCount)) & UintMask;
            range = (range*(SubRange.HighCount - SubRange.LowCount)) & UintMask;
        }

        internal void AriDecNormalize()
        {
            //		while ((low ^ (low + range)) < TOP || range < BOT && ((range = -low & (BOT - 1)) != 0 ? true : true)) 
            //		{
            //			code = ((code << 8) | unpackRead.getChar()&0xff)&uintMask;
            //			range = (range << 8)&uintMask;
            //			low = (low << 8)&uintMask;
            //		}

            // Rewrote for clarity
            bool c2 = false;
            while ((low ^ (low + range)) < TOP || (c2 = range < BOT))
            {
                if (c2)
                {
                    range = (-low & (BOT - 1)) & UintMask;
                    c2 = false;
                }
                code = ((code << 8) | Char) & UintMask;
                range = (range << 8) & UintMask;
                low = (low << 8) & UintMask;
            }
        }

        // Debug
        public override System.String ToString()
        {
            StringBuilder buffer = new StringBuilder();
            buffer.Append("RangeCoder[");
            buffer.Append("\n  low=");
            buffer.Append(low);
            buffer.Append("\n  code=");
            buffer.Append(code);
            buffer.Append("\n  range=");
            buffer.Append(range);
            buffer.Append("\n  subrange=");
            buffer.Append(SubRange);
            buffer.Append("]");
            return buffer.ToString();
        }
    }

    internal class SubRange
    {
        // uint LowCount, HighCount, scale;
        private long lowCount, highCount, scale;

        internal void incScale(int dScale)
        {
            Scale = Scale + dScale;
        }

        internal long HighCount
        {
            get { return highCount; }

            set { this.highCount = value & RangeCoder.UintMask; }
        }

        internal long LowCount
        {
            get { return lowCount & RangeCoder.UintMask; }

            set { this.lowCount = value & RangeCoder.UintMask; }
        }

        internal long Scale
        {
            get { return scale; }

            set { this.scale = value & RangeCoder.UintMask; }
        }

        // Debug
        public override System.String ToString()
        {
            StringBuilder buffer = new StringBuilder();
            buffer.Append("SubRange[");
            buffer.Append("\n  lowCount=");
            buffer.Append(lowCount);
            buffer.Append("\n  highCount=");
            buffer.Append(highCount);
            buffer.Append("\n  scale=");
            buffer.Append(scale);
            buffer.Append("]");
            return buffer.ToString();
        }
    }
}