InternalDecoderBestFitFallbackBuffer.cs

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using System.Threading;
 
namespace System.Text;
 
internal sealed class InternalDecoderBestFitFallbackBuffer : DecoderFallbackBuffer
{
    internal char cBestFit;
 
    internal int iCount = -1;
 
    internal int iSize;
 
    private readonly InternalDecoderBestFitFallback _oFallback;
 
    private static object s_InternalSyncObject;
 
    private static object InternalSyncObject
    {
        get
        {
            if (s_InternalSyncObject == null)
            {
                object value = new object();
                Interlocked.CompareExchange<object>(ref s_InternalSyncObject, value, (object)null);
            }
            return s_InternalSyncObject;
        }
    }
 
    public override int Remaining
    {
        get
        {
            if (iCount <= 0)
            {
                return 0;
            }
            return iCount;
        }
    }
 
    public InternalDecoderBestFitFallbackBuffer(InternalDecoderBestFitFallback fallback)
    {
        _oFallback = fallback;
        if (_oFallback.arrayBestFit != null)
        {
            return;
        }
        lock (InternalSyncObject)
        {
            if (_oFallback.arrayBestFit == null)
            {
                _oFallback.arrayBestFit = fallback.encoding.GetBestFitBytesToUnicodeData();
            }
        }
    }
 
    public override bool Fallback(byte[] bytesUnknown, int index)
    {
        cBestFit = TryBestFit(bytesUnknown);
        if (cBestFit == '\0')
        {
            cBestFit = _oFallback.cReplacement;
        }
        iCount = (iSize = 1);
        return true;
    }
 
    public override char GetNextChar()
    {
        iCount--;
        if (iCount < 0)
        {
            return '\0';
        }
        if (iCount == int.MaxValue)
        {
            iCount = -1;
            return '\0';
        }
        return cBestFit;
    }
 
    public override bool MovePrevious()
    {
        if (iCount >= 0)
        {
            iCount++;
        }
        if (iCount >= 0)
        {
            return iCount <= iSize;
        }
        return false;
    }
 
    public override void Reset()
    {
        iCount = -1;
    }
 
    private char TryBestFit(byte[] bytesCheck)
    {
        int num = 0;
        int num2 = _oFallback.arrayBestFit.Length;
        if (num2 == 0)
        {
            return '\0';
        }
        if (bytesCheck.Length == 0 || bytesCheck.Length > 2)
        {
            return '\0';
        }
        char c = ((bytesCheck.Length != 1) ? ((char)((bytesCheck[0] << 8) + bytesCheck[1])) : ((char)bytesCheck[0]));
        if (c < _oFallback.arrayBestFit[0] || c > _oFallback.arrayBestFit[num2 - 2])
        {
            return '\0';
        }
        int num3;
        while ((num3 = num2 - num) > 6)
        {
            int num4 = (num3 / 2 + num) & 0xFFFE;
            char c2 = _oFallback.arrayBestFit[num4];
            if (c2 == c)
            {
                return _oFallback.arrayBestFit[num4 + 1];
            }
            if (c2 < c)
            {
                num = num4;
            }
            else
            {
                num2 = num4;
            }
        }
        for (int num4 = num; num4 < num2; num4 += 2)
        {
            if (_oFallback.arrayBestFit[num4] == c)
            {
                return _oFallback.arrayBestFit[num4 + 1];
            }
        }
        return '\0';
    }
}