DecoderBestFitFallback.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Text / DecoderBestFitFallback.cs / 1 / DecoderBestFitFallback.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// DecoderBestFitFallback.cs
// 
// This is used internally to create best fit behavior as per the original windows best fit behavior. 
//
namespace System.Text 
{
    using System;
    using System.Text;
    using System.Threading; 

    [Serializable()] 
    internal sealed class InternalDecoderBestFitFallback : DecoderFallback 
    {
        // Our variables 
        internal Encoding encoding = null;
        internal char[]   arrayBestFit = null;
        internal char     cReplacement = '?';
 
        internal InternalDecoderBestFitFallback(Encoding encoding)
        { 
            // Need to load our replacement characters table. 
            this.encoding = encoding;
            this.bIsMicrosoftBestFitFallback = true; 
        }

        public override DecoderFallbackBuffer CreateFallbackBuffer()
        { 
            return new InternalDecoderBestFitFallbackBuffer(this);
        } 
 
        // Maximum number of characters that this instance of this fallback could return
        public override int MaxCharCount 
        {
            get
            {
                return 1; 
            }
        } 
 
        public override bool Equals(Object value)
        { 
            InternalDecoderBestFitFallback that = value as InternalDecoderBestFitFallback;
            if (that != null)
            {
                return (this.encoding.CodePage == that.encoding.CodePage); 
            }
            return (false); 
        } 

        public override int GetHashCode() 
        {
            return this.encoding.CodePage;
        }
    } 

    internal sealed class InternalDecoderBestFitFallbackBuffer : DecoderFallbackBuffer 
    { 
        // Our variables
        internal char                   cBestFit = '\0'; 
        internal int                    iCount = -1;
        internal int                    iSize;
        private InternalDecoderBestFitFallback  oFallback;
 
        // Private object for locking instead of locking on a public type for SQL reliability work.
        private static Object s_InternalSyncObject; 
        private static Object InternalSyncObject 
        {
            get 
            {
                if (s_InternalSyncObject == null)
                {
                    Object o = new Object(); 
                    Interlocked.CompareExchange(ref s_InternalSyncObject, o, null);
                } 
                return s_InternalSyncObject; 
            }
        } 

        // Constructor
        public InternalDecoderBestFitFallbackBuffer(InternalDecoderBestFitFallback fallback)
        { 
            this.oFallback = fallback;
 
            if (oFallback.arrayBestFit == null) 
            {
                // Lock so we don't confuse ourselves. 
                lock(InternalSyncObject)
                {
                    // Double check before we do it again.
                    if (oFallback.arrayBestFit == null) 
                        oFallback.arrayBestFit = fallback.encoding.GetBestFitBytesToUnicodeData();
                } 
            } 
        }
 
        // Fallback methods
        public override bool Fallback(byte[] bytesUnknown, int index)
        {
            // We expect no previous fallback in our buffer 
            BCLDebug.Assert(iCount < 1, "[DecoderReplacementFallbackBuffer.Fallback] Calling fallback without a previously empty buffer");
 
            cBestFit = TryBestFit(bytesUnknown); 
            if (cBestFit == '\0')
                cBestFit = oFallback.cReplacement; 

            iCount = iSize = 1;

            return true; 
        }
 
        // Default version is overridden in DecoderReplacementFallback.cs 
        public override char GetNextChar()
        { 
            // Just return cReturn, which is 0 if there's no best fit for it.
            return (iCount-- > 0) ? cBestFit : '\0';
        }
 
        public override bool MovePrevious()
        { 
            // Exception fallback doesn't have anywhere to back up to. 
            if (iCount >= 0)
                iCount++; 

            // Return true if we could do it.
            return (iCount >= 0 && iCount <= iSize);
        } 

        // How many characters left to output? 
        public override int Remaining 
        {
            get 
            {
                return (iCount > 0) ? iCount : 0;
            }
        } 

        // Clear the buffer 
        public override unsafe void Reset() 
        {
            iCount = -1; 
            byteStart = null;
        }

        // This version just counts the fallback and doesn't actually copy anything. 
        internal unsafe override int InternalFallback(byte[] bytes, byte* pBytes)
        // Right now this has both bytes and bytes[], since we might have extra bytes, hence the 
        // array, and we might need the index, hence the byte* 
        {
            // return our replacement string Length (always 1 for InternalDecoderBestFitFallback, either 
            // a best fit char or ?
            return 1;
        }
 
        // private helper methods
        private char TryBestFit(byte[] bytesCheck) 
        { 
            // Need to figure out our best fit character, low is beginning of array, high is 1 AFTER end of array
            int lowBound = 0; 
            int highBound = oFallback.arrayBestFit.Length;
            int index;
            char cCheck;
 
            // Check trivial case first (no best fit)
            if (highBound == 0) 
                return '\0'; 

            // If our array is too small or too big we can't check 
            if (bytesCheck.Length == 0 || bytesCheck.Length > 2)
                return '\0';

            if (bytesCheck.Length == 1) 
                cCheck = unchecked((char)bytesCheck[0]);
            else 
                cCheck = unchecked((char)((bytesCheck[0] << 8) + bytesCheck[1])); 

            // Check trivial out of range case 
            if (cCheck < oFallback.arrayBestFit[0] || cCheck > oFallback.arrayBestFit[highBound - 2])
                return '\0';

            // Binary search the array 
            int iDiff;
            while ((iDiff = (highBound - lowBound)) > 6) 
            { 
                // Look in the middle, which is complicated by the fact that we have 2 #s for each pair,
                // so we don't want index to be odd because it must be word aligned. 
                // Also note that index can never == highBound (because diff is rounded down)
                index = ((iDiff / 2) + lowBound) & 0xFFFE;

                char cTest = oFallback.arrayBestFit[index]; 
                if (cTest == cCheck)
                { 
                    // We found it 
                    BCLDebug.Assert(index + 1 < oFallback.arrayBestFit.Length,
                        "[InternalDecoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array"); 
                    return oFallback.arrayBestFit[index + 1];
                }
                else if (cTest < cCheck)
                { 
                    // We weren't high enough
                    lowBound = index; 
                } 
                else
                { 
                    // We weren't low enough
                    highBound = index;
                }
            } 

            for (index = lowBound; index < highBound; index += 2) 
            { 
                if (oFallback.arrayBestFit[index] == cCheck)
                { 
                    // We found it
                    BCLDebug.Assert(index + 1 < oFallback.arrayBestFit.Length,
                        "[InternalDecoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array");
                    return oFallback.arrayBestFit[index + 1]; 
                }
            } 
 
            // Char wasn't in our table
            return '\0'; 
        }
    }
}

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