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// ==++==
//
// 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;
using System.Diagnostics.Contracts;
[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<Object>(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
Contract.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()
{
// We want it to get < 0 because == 0 means that the current/last character is a fallback
// and we need to detect recursion. We could have a flag but we already have this counter.
iCount--;
// Do we have anything left? 0 is now last fallback char, negative is nothing left
if (iCount < 0)
return '\0';
// Need to get it out of the buffer.
// Make sure it didn't wrap from the fast count-- path
if (iCount == int.MaxValue)
{
iCount = -1;
return '\0';
}
// Return the best fit character
return cBestFit;
}
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
[System.Security.SecuritySafeCritical] // overrides public transparent member
public override unsafe void Reset()
{
iCount = -1;
byteStart = null;
}
// This version just counts the fallback and doesn't actually copy anything.
[System.Security.SecurityCritical] // auto-generated
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
Contract.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
Contract.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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