EncoderBestFitFallback.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Text / EncoderBestFitFallback.cs / 1 / EncoderBestFitFallback.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// EncoderBestFitFallback.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.Globalization;
    using System.Text; 
    using System.Threading;
 
    [Serializable()] 
    internal class InternalEncoderBestFitFallback : EncoderFallback
    { 
        // Our variables
        internal Encoding encoding = null;
        internal char[]   arrayBestFit = null;
 
        internal InternalEncoderBestFitFallback(Encoding encoding)
        { 
            // Need to load our replacement characters table. 
            this.encoding = encoding;
            this.bIsMicrosoftBestFitFallback = true; 
        }

        public override EncoderFallbackBuffer CreateFallbackBuffer()
        { 
            return new InternalEncoderBestFitFallbackBuffer(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)
        { 
            InternalEncoderBestFitFallback that = value as InternalEncoderBestFitFallback;
            if (that != null)
            {
                return (this.encoding.CodePage == that.encoding.CodePage); 
            }
            return (false); 
        } 

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

    internal sealed class InternalEncoderBestFitFallbackBuffer : EncoderFallbackBuffer 
    { 
        // Our variables
        private char                    cBestFit = '\0'; 
        private InternalEncoderBestFitFallback  oFallback;
        private int                     iCount = -1;
        private int                     iSize;
 
        // 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 InternalEncoderBestFitFallbackBuffer(InternalEncoderBestFitFallback 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.GetBestFitUnicodeToBytesData();
                } 
            } 
        }
 
        // Fallback methods
        public override bool Fallback(char charUnknown, int index)
        {
            // If we had a buffer already we're being recursive, throw, it's probably at the suspect 
            // character in our array.
            // Shouldn't be able to get here for all of our code pages, table would have to be messed up. 
            BCLDebug.Assert(iCount < 1, "[InternalEncoderBestFitFallbackBuffer.Fallback(non surrogate)] Fallback char " + ((int)cBestFit).ToString("X4", CultureInfo.InvariantCulture) + " caused recursive fallback"); 

            iCount = iSize = 1; 
            cBestFit = TryBestFit(charUnknown);
            if (cBestFit == '\0')
                cBestFit = '?';
 
            return true;
        } 
 
        public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index)
        { 
            // Double check input surrogate pair
            if (!Char.IsHighSurrogate(charUnknownHigh))
                throw new ArgumentOutOfRangeException("charUnknownHigh",
                    Environment.GetResourceString("ArgumentOutOfRange_Range", 
                    0xD800, 0xDBFF));
 
            if (!Char.IsLowSurrogate(charUnknownLow)) 
                throw new ArgumentOutOfRangeException("CharUnknownLow",
                    Environment.GetResourceString("ArgumentOutOfRange_Range", 
                    0xDC00, 0xDFFF));

            // If we had a buffer already we're being recursive, throw, it's probably at the suspect
            // character in our array.  0 is processing last character, < 0 is not falling back 
            // Shouldn't be able to get here, table would have to be messed up.
            BCLDebug.Assert(iCount < 1, "[InternalEncoderBestFitFallbackBuffer.Fallback(surrogate)] Fallback char " + ((int)cBestFit).ToString("X4", CultureInfo.InvariantCulture) + " caused recursive fallback"); 
 
            // Go ahead and get our fallback, surrogates don't have best fit
            cBestFit = '?'; 
            iCount = iSize = 2;

            return true;
        } 

        // Default version is overridden in EncoderReplacementFallback.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; 
            charStart = null;
            bFallingBack = false;
        }
 
        // private helper methods
        private char TryBestFit(char cUnknown) 
        { 
            // 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;

            // 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 we want to be on word boundaries. 
                // Also note that index can never == highBound (because diff is rounded down)
                index = ((iDiff / 2) + lowBound) & 0xFFFE;

                char cTest = oFallback.arrayBestFit[index]; 
                if (cTest == cUnknown)
                { 
                    // We found it 
                    BCLDebug.Assert(index + 1 < oFallback.arrayBestFit.Length,
                        "[InternalEncoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array"); 
                    return oFallback.arrayBestFit[index + 1];
                }
                else if (cTest < cUnknown)
                { 
                    // 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] == cUnknown)
                { 
                    // We found it
                    BCLDebug.Assert(index + 1 < oFallback.arrayBestFit.Length,
                        "[InternalEncoderBestFitFallbackBuffer.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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EncoderBestFitFallback.cs source code in C# .NET

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