BaseCodePageEncoding.cs source code in C# .NET

Source code for the .NET framework in C#

                        

Code:

/ Dotnetfx_Vista_SP2 / Dotnetfx_Vista_SP2 / 8.0.50727.4016 / DEVDIV / depot / DevDiv / releases / whidbey / NetFxQFE / ndp / clr / src / BCL / System / Text / BaseCodePageEncoding.cs / 1 / BaseCodePageEncoding.cs

                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
namespace System.Text
{ 
    using System; 
    using System.Globalization;
    using System.Runtime.InteropServices; 
    using System.Security;
    using System.Collections;
    using System.Runtime.CompilerServices;
    using System.Runtime.Serialization; 
    using System.Security.Permissions;
    using Microsoft.Win32.SafeHandles; 
 
    // Our input file data structures look like:
    // 
    // Header Structure Looks Like:
    //   struct NLSPlusHeader
    //   {
    //       WORD[16]    filename;       // 32 bytes 
    //       WORD[4]     version;        // 8 bytes = 40     // I.e: 3, 2, 0, 0
    //       WORD        count;          // 2 bytes = 42     // Number of code page index's that'll follow 
    //   } 
    //
    // Each code page section looks like: 
    //   struct NLSCodePageIndex
    //   {
    //       WORD[16]    codePageName;   // 32 bytes
    //       WORD        codePage;       // +2 bytes = 34 
    //       WORD        byteCount;      // +2 bytes = 36
    //       DWORD       offset;         // +4 bytes = 40    // Bytes from beginning of FILE. 
    //   } 
    //
    // Each code page then has its own header 
    //   struct NLSCodePage
    //   {
    //       WORD[16]    codePageName;   // 32 bytes
    //       WORD[4]     version;        // 8 bytes = 40     // I.e: 3.2.0.0 
    //       WORD        codePage;       // 2 bytes = 42
    //       WORD        byteCount;      // 2 bytes = 44     // 1 or 2 byte code page (SBCS or DBCS) 
    //       WORD        unicodeReplace; // 2 bytes = 46     // default replacement unicode character 
    //       WORD        byteReplace;    // 2 bytes = 48     // default replacement byte(s)
    //       BYTE[]      data;           // data section 
    //   }

    [Serializable()] internal abstract class BaseCodePageEncoding : EncodingNLS, ISerializable
    { 
        // Static & Const stuff
        internal const String CODE_PAGE_DATA_FILE_NAME = "codepages.nlp"; 
        [NonSerialized] 
        protected int dataTableCodePage;
 
        // Variables to help us allocate/mark our memory section correctly
        [NonSerialized]
        protected bool bFlagDataTable = true;
        [NonSerialized] 
        protected int iExtraBytes = 0;
 
        // Our private unicode to bytes best fit array and visa versa. 
        [NonSerialized]
        protected char[] arrayUnicodeBestFit = null; 
        [NonSerialized]
        protected char[] arrayBytesBestFit = null;

        // This is used to help ISCII, EUCJP and ISO2022 figure out they're MlangEncodings 
        [NonSerialized]
        protected bool m_bUseMlangTypeForSerialization = false; 
 
        //
        // This is the header for the native data table that we load from CODE_PAGE_DATA_FILE_NAME. 
        //
        // Explicit layout is used here since a syntax like char[16] can not be used in sequential layout.
        [StructLayout(LayoutKind.Explicit)]
        internal unsafe struct CodePageDataFileHeader 
        {
            [FieldOffset(0)] 
            internal char TableName;            // WORD[16] 
            [FieldOffset(0x20)]
            internal ushort Version;            // WORD[4] 
            [FieldOffset(0x28)]
            internal short CodePageCount;       // WORD
            [FieldOffset(0x2A)]
            internal short unused1;             // Add a unused WORD so that CodePages is aligned with DWORD boundary. 
                                                // Otherwise, 64-bit version will fail.
            [FieldOffset(0x2C)] 
            internal CodePageIndex CodePages;   // Start of code page index 
        }
 
        [StructLayout(LayoutKind.Explicit, Pack=2)]
        internal unsafe struct CodePageIndex
        {
            [FieldOffset(0)] 
            internal char CodePageName;     // WORD[16]
            [FieldOffset(0x20)] 
            internal short CodePage;        // WORD 
            [FieldOffset(0x22)]
            internal short ByteCount;       // WORD 
            [FieldOffset(0x24)]
            internal int Offset;            // DWORD
        }
 
        [StructLayout(LayoutKind.Explicit)]
        internal unsafe struct CodePageHeader 
        { 
            [FieldOffset(0)]
            internal char CodePageName;     // WORD[16] 
            [FieldOffset(0x20)]
            internal ushort VersionMajor;   // WORD
            [FieldOffset(0x22)]
            internal ushort VersionMinor;   // WORD 
            [FieldOffset(0x24)]
            internal ushort VersionRevision;// WORD 
            [FieldOffset(0x26)] 
            internal ushort VersionBuild;   // WORD
            [FieldOffset(0x28)] 
            internal short CodePage;        // WORD
            [FieldOffset(0x2a)]
            internal short ByteCount;       // WORD     // 1 or 2 byte code page (SBCS or DBCS)
            [FieldOffset(0x2c)] 
            internal char UnicodeReplace;   // WORD     // default replacement unicode character
            [FieldOffset(0x2e)] 
            internal ushort ByteReplace;    // WORD     // default replacement bytes 
            [FieldOffset(0x30)]
            internal short FirstDataWord;   // WORD[] 
        }

        // Initialize our global stuff
        unsafe static CodePageDataFileHeader* m_pCodePageFileHeader = 
            (CodePageDataFileHeader*)GlobalizationAssembly.GetGlobalizationResourceBytePtr(
                typeof(CharUnicodeInfo).Assembly, CODE_PAGE_DATA_FILE_NAME); 
 
        // Real variables
        [NonSerialized] 
        unsafe protected CodePageHeader* pCodePage = null;

        // Safe handle wrapper around section map view
        [NonSerialized] 
        protected SafeViewOfFileHandle safeMemorySectionHandle = null;
 
        // Safe handle wrapper around mapped file handle 
        [NonSerialized]
        protected SafeFileMappingHandle safeFileMappingHandle = null; 

        internal BaseCodePageEncoding(int codepage) : this(codepage, codepage)
        {
        } 

        internal BaseCodePageEncoding(int codepage, int dataCodePage) : 
            base(codepage == 0? Microsoft.Win32.Win32Native.GetACP(): codepage) 
        {
            // Remember number of code page that we'll be using the table for. 
            dataTableCodePage = dataCodePage;
            LoadCodePageTables();
        }
 
        // Constructor called by serialization.
        internal BaseCodePageEncoding(SerializationInfo info, StreamingContext context) : base(0) 
        { 
            // We cannot ever call this, we've proxied ourselved to CodePageEncoding
            throw new ArgumentNullException("this"); 
        }

        // ISerializable implementation
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.SerializationFormatter)] 
        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
        { 
            // Make sure to get teh base stuff too This throws if info is null 
            SerializeEncoding(info, context);
            BCLDebug.Assert(info!=null, "[BaseCodePageEncoding.GetObjectData] Expected null info to throw"); 

            // Just need Everett maxCharSize (BaseCodePageEncoding) or m_maxByteSize (MLangBaseCodePageEncoding)
            info.AddValue(m_bUseMlangTypeForSerialization ? "m_maxByteSize" : "maxCharSize",
                          this.IsSingleByte ? 1 : 2); 

            // Use this class or MLangBaseCodePageEncoding as our deserializer. 
            info.SetType(m_bUseMlangTypeForSerialization ? typeof(MLangCodePageEncoding) : 
                                                           typeof(CodePageEncoding));
        } 

        // We need to load tables for our code page
        private unsafe void LoadCodePageTables()
        { 
            CodePageHeader* pCodePage = FindCodePage(dataTableCodePage);
 
            // Make sure we have one 
            if (pCodePage == null)
            { 
                // Didn't have one
                throw new NotSupportedException(
                    Environment.GetResourceString("NotSupported_NoCodepageData", CodePage));
            } 

            // Remember our code page 
            this.pCodePage = pCodePage; 

            // We had it, so load it 
            LoadManagedCodePage();
        }

        // Look up the code page pointer 
        private static unsafe CodePageHeader* FindCodePage(int codePage)
        { 
            // We'll have to loop through all of the m_pCodePageIndex[] items to find our code page, this isn't 
            // binary or anything so its not monsterously fast.
            for (int i = 0; i < m_pCodePageFileHeader->CodePageCount; i++) 
            {
                CodePageIndex* pCodePageIndex = (&(m_pCodePageFileHeader->CodePages)) + i;

                if (pCodePageIndex->CodePage == codePage) 
                {
                    // Found it! 
                    CodePageHeader* pCodePage = 
                        (CodePageHeader*)((byte*)m_pCodePageFileHeader + pCodePageIndex->Offset);
                    return pCodePage; 
                }
            }

            // Couldn't find it 
            return null;
        } 
 
        // Get our code page byte count
        internal static unsafe int GetCodePageByteSize(int codePage) 
        {
            // Get our code page info
            CodePageHeader* pCodePage = FindCodePage(codePage);
 
            // If null return 0
            if (pCodePage == null) 
                return 0; 

            BCLDebug.Assert(pCodePage->ByteCount == 1 || pCodePage->ByteCount == 2, 
                "[BaseCodePageEncoding] Code page (" + codePage + ") has invalid byte size (" + pCodePage->ByteCount + ") in table");
            // Return what it says for byte count
            return pCodePage->ByteCount;
        } 

        // We have a managed code page entry, so load our tables 
        protected abstract unsafe void LoadManagedCodePage(); 

        // Allocate memory to load our code page 
        protected unsafe byte* GetSharedMemory(int iSize)
        {
            // Build our name
            String strName = GetMemorySectionName(); 

            IntPtr mappedFileHandle; 
 
            // This gets shared memory for our map.  If its can't, it gives us clean memory.
            Byte *pMemorySection = EncodingTable.nativeCreateOpenFileMapping(strName, iSize, out mappedFileHandle); 
            BCLDebug.Assert(pMemorySection != null,
                "[BaseCodePageEncoding.GetSharedMemory] Expected non-null memory section to be opened");

            // If that failed, we have to die. 
            if (pMemorySection == null)
                throw new OutOfMemoryException( 
                    Environment.GetResourceString("Arg_OutOfMemoryException")); 

            // if we have null file handle. this means memory was allocated after 
            // failing to open the mapped file.

            if (mappedFileHandle != IntPtr.Zero)
            { 
                safeMemorySectionHandle = new SafeViewOfFileHandle((IntPtr) pMemorySection, true);
                safeFileMappingHandle = new SafeFileMappingHandle(mappedFileHandle, true); 
            } 

            return pMemorySection; 
        }

        protected unsafe virtual String GetMemorySectionName()
        { 
            int iUseCodePage = this.bFlagDataTable ? dataTableCodePage : CodePage;
 
            String strName = String.Format(CultureInfo.InvariantCulture, "NLS_CodePage_{0}_{1}_{2}_{3}_{4}", 
                iUseCodePage, this.pCodePage->VersionMajor, this.pCodePage->VersionMinor,
                this.pCodePage->VersionRevision, this.pCodePage->VersionBuild); 

            return strName;
        }
 
        protected abstract unsafe void ReadBestFitTable();
 
        internal override char[] GetBestFitUnicodeToBytesData() 
        {
            // Read in our best fit table if necessary 
            if (arrayUnicodeBestFit == null) ReadBestFitTable();

            BCLDebug.Assert(arrayUnicodeBestFit != null,
                "[BaseCodePageEncoding.GetBestFitUnicodeToBytesData]Expected non-null arrayUnicodeBestFit"); 

            // Normally we don't have any best fit data. 
            return arrayUnicodeBestFit; 
        }
 
        internal override char[] GetBestFitBytesToUnicodeData()
        {
            // Read in our best fit table if necessary
            if (arrayUnicodeBestFit == null) ReadBestFitTable(); 

            BCLDebug.Assert(arrayBytesBestFit != null, 
                "[BaseCodePageEncoding.GetBestFitBytesToUnicodeData]Expected non-null arrayBytesBestFit"); 

            // Normally we don't have any best fit data. 
            return arrayBytesBestFit;
        }

        // During the AppDomain shutdown the Encoding class may already finalized and the memory section 
        // is invalid. so we detect that by validating the memory section handle then re-initialize the memory
        // section by calling LoadManagedCodePage() method and eventually the mapped file handle and 
        // the memory section pointer will get finalized one more time. 
        internal unsafe void CheckMemorySection()
        { 
            if (safeMemorySectionHandle != null && safeMemorySectionHandle.DangerousGetHandle() == IntPtr.Zero)
            {
                LoadManagedCodePage();
            } 
        }
    } 
} 


// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
namespace System.Text
{ 
    using System; 
    using System.Globalization;
    using System.Runtime.InteropServices; 
    using System.Security;
    using System.Collections;
    using System.Runtime.CompilerServices;
    using System.Runtime.Serialization; 
    using System.Security.Permissions;
    using Microsoft.Win32.SafeHandles; 
 
    // Our input file data structures look like:
    // 
    // Header Structure Looks Like:
    //   struct NLSPlusHeader
    //   {
    //       WORD[16]    filename;       // 32 bytes 
    //       WORD[4]     version;        // 8 bytes = 40     // I.e: 3, 2, 0, 0
    //       WORD        count;          // 2 bytes = 42     // Number of code page index's that'll follow 
    //   } 
    //
    // Each code page section looks like: 
    //   struct NLSCodePageIndex
    //   {
    //       WORD[16]    codePageName;   // 32 bytes
    //       WORD        codePage;       // +2 bytes = 34 
    //       WORD        byteCount;      // +2 bytes = 36
    //       DWORD       offset;         // +4 bytes = 40    // Bytes from beginning of FILE. 
    //   } 
    //
    // Each code page then has its own header 
    //   struct NLSCodePage
    //   {
    //       WORD[16]    codePageName;   // 32 bytes
    //       WORD[4]     version;        // 8 bytes = 40     // I.e: 3.2.0.0 
    //       WORD        codePage;       // 2 bytes = 42
    //       WORD        byteCount;      // 2 bytes = 44     // 1 or 2 byte code page (SBCS or DBCS) 
    //       WORD        unicodeReplace; // 2 bytes = 46     // default replacement unicode character 
    //       WORD        byteReplace;    // 2 bytes = 48     // default replacement byte(s)
    //       BYTE[]      data;           // data section 
    //   }

    [Serializable()] internal abstract class BaseCodePageEncoding : EncodingNLS, ISerializable
    { 
        // Static & Const stuff
        internal const String CODE_PAGE_DATA_FILE_NAME = "codepages.nlp"; 
        [NonSerialized] 
        protected int dataTableCodePage;
 
        // Variables to help us allocate/mark our memory section correctly
        [NonSerialized]
        protected bool bFlagDataTable = true;
        [NonSerialized] 
        protected int iExtraBytes = 0;
 
        // Our private unicode to bytes best fit array and visa versa. 
        [NonSerialized]
        protected char[] arrayUnicodeBestFit = null; 
        [NonSerialized]
        protected char[] arrayBytesBestFit = null;

        // This is used to help ISCII, EUCJP and ISO2022 figure out they're MlangEncodings 
        [NonSerialized]
        protected bool m_bUseMlangTypeForSerialization = false; 
 
        //
        // This is the header for the native data table that we load from CODE_PAGE_DATA_FILE_NAME. 
        //
        // Explicit layout is used here since a syntax like char[16] can not be used in sequential layout.
        [StructLayout(LayoutKind.Explicit)]
        internal unsafe struct CodePageDataFileHeader 
        {
            [FieldOffset(0)] 
            internal char TableName;            // WORD[16] 
            [FieldOffset(0x20)]
            internal ushort Version;            // WORD[4] 
            [FieldOffset(0x28)]
            internal short CodePageCount;       // WORD
            [FieldOffset(0x2A)]
            internal short unused1;             // Add a unused WORD so that CodePages is aligned with DWORD boundary. 
                                                // Otherwise, 64-bit version will fail.
            [FieldOffset(0x2C)] 
            internal CodePageIndex CodePages;   // Start of code page index 
        }
 
        [StructLayout(LayoutKind.Explicit, Pack=2)]
        internal unsafe struct CodePageIndex
        {
            [FieldOffset(0)] 
            internal char CodePageName;     // WORD[16]
            [FieldOffset(0x20)] 
            internal short CodePage;        // WORD 
            [FieldOffset(0x22)]
            internal short ByteCount;       // WORD 
            [FieldOffset(0x24)]
            internal int Offset;            // DWORD
        }
 
        [StructLayout(LayoutKind.Explicit)]
        internal unsafe struct CodePageHeader 
        { 
            [FieldOffset(0)]
            internal char CodePageName;     // WORD[16] 
            [FieldOffset(0x20)]
            internal ushort VersionMajor;   // WORD
            [FieldOffset(0x22)]
            internal ushort VersionMinor;   // WORD 
            [FieldOffset(0x24)]
            internal ushort VersionRevision;// WORD 
            [FieldOffset(0x26)] 
            internal ushort VersionBuild;   // WORD
            [FieldOffset(0x28)] 
            internal short CodePage;        // WORD
            [FieldOffset(0x2a)]
            internal short ByteCount;       // WORD     // 1 or 2 byte code page (SBCS or DBCS)
            [FieldOffset(0x2c)] 
            internal char UnicodeReplace;   // WORD     // default replacement unicode character
            [FieldOffset(0x2e)] 
            internal ushort ByteReplace;    // WORD     // default replacement bytes 
            [FieldOffset(0x30)]
            internal short FirstDataWord;   // WORD[] 
        }

        // Initialize our global stuff
        unsafe static CodePageDataFileHeader* m_pCodePageFileHeader = 
            (CodePageDataFileHeader*)GlobalizationAssembly.GetGlobalizationResourceBytePtr(
                typeof(CharUnicodeInfo).Assembly, CODE_PAGE_DATA_FILE_NAME); 
 
        // Real variables
        [NonSerialized] 
        unsafe protected CodePageHeader* pCodePage = null;

        // Safe handle wrapper around section map view
        [NonSerialized] 
        protected SafeViewOfFileHandle safeMemorySectionHandle = null;
 
        // Safe handle wrapper around mapped file handle 
        [NonSerialized]
        protected SafeFileMappingHandle safeFileMappingHandle = null; 

        internal BaseCodePageEncoding(int codepage) : this(codepage, codepage)
        {
        } 

        internal BaseCodePageEncoding(int codepage, int dataCodePage) : 
            base(codepage == 0? Microsoft.Win32.Win32Native.GetACP(): codepage) 
        {
            // Remember number of code page that we'll be using the table for. 
            dataTableCodePage = dataCodePage;
            LoadCodePageTables();
        }
 
        // Constructor called by serialization.
        internal BaseCodePageEncoding(SerializationInfo info, StreamingContext context) : base(0) 
        { 
            // We cannot ever call this, we've proxied ourselved to CodePageEncoding
            throw new ArgumentNullException("this"); 
        }

        // ISerializable implementation
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.SerializationFormatter)] 
        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
        { 
            // Make sure to get teh base stuff too This throws if info is null 
            SerializeEncoding(info, context);
            BCLDebug.Assert(info!=null, "[BaseCodePageEncoding.GetObjectData] Expected null info to throw"); 

            // Just need Everett maxCharSize (BaseCodePageEncoding) or m_maxByteSize (MLangBaseCodePageEncoding)
            info.AddValue(m_bUseMlangTypeForSerialization ? "m_maxByteSize" : "maxCharSize",
                          this.IsSingleByte ? 1 : 2); 

            // Use this class or MLangBaseCodePageEncoding as our deserializer. 
            info.SetType(m_bUseMlangTypeForSerialization ? typeof(MLangCodePageEncoding) : 
                                                           typeof(CodePageEncoding));
        } 

        // We need to load tables for our code page
        private unsafe void LoadCodePageTables()
        { 
            CodePageHeader* pCodePage = FindCodePage(dataTableCodePage);
 
            // Make sure we have one 
            if (pCodePage == null)
            { 
                // Didn't have one
                throw new NotSupportedException(
                    Environment.GetResourceString("NotSupported_NoCodepageData", CodePage));
            } 

            // Remember our code page 
            this.pCodePage = pCodePage; 

            // We had it, so load it 
            LoadManagedCodePage();
        }

        // Look up the code page pointer 
        private static unsafe CodePageHeader* FindCodePage(int codePage)
        { 
            // We'll have to loop through all of the m_pCodePageIndex[] items to find our code page, this isn't 
            // binary or anything so its not monsterously fast.
            for (int i = 0; i < m_pCodePageFileHeader->CodePageCount; i++) 
            {
                CodePageIndex* pCodePageIndex = (&(m_pCodePageFileHeader->CodePages)) + i;

                if (pCodePageIndex->CodePage == codePage) 
                {
                    // Found it! 
                    CodePageHeader* pCodePage = 
                        (CodePageHeader*)((byte*)m_pCodePageFileHeader + pCodePageIndex->Offset);
                    return pCodePage; 
                }
            }

            // Couldn't find it 
            return null;
        } 
 
        // Get our code page byte count
        internal static unsafe int GetCodePageByteSize(int codePage) 
        {
            // Get our code page info
            CodePageHeader* pCodePage = FindCodePage(codePage);
 
            // If null return 0
            if (pCodePage == null) 
                return 0; 

            BCLDebug.Assert(pCodePage->ByteCount == 1 || pCodePage->ByteCount == 2, 
                "[BaseCodePageEncoding] Code page (" + codePage + ") has invalid byte size (" + pCodePage->ByteCount + ") in table");
            // Return what it says for byte count
            return pCodePage->ByteCount;
        } 

        // We have a managed code page entry, so load our tables 
        protected abstract unsafe void LoadManagedCodePage(); 

        // Allocate memory to load our code page 
        protected unsafe byte* GetSharedMemory(int iSize)
        {
            // Build our name
            String strName = GetMemorySectionName(); 

            IntPtr mappedFileHandle; 
 
            // This gets shared memory for our map.  If its can't, it gives us clean memory.
            Byte *pMemorySection = EncodingTable.nativeCreateOpenFileMapping(strName, iSize, out mappedFileHandle); 
            BCLDebug.Assert(pMemorySection != null,
                "[BaseCodePageEncoding.GetSharedMemory] Expected non-null memory section to be opened");

            // If that failed, we have to die. 
            if (pMemorySection == null)
                throw new OutOfMemoryException( 
                    Environment.GetResourceString("Arg_OutOfMemoryException")); 

            // if we have null file handle. this means memory was allocated after 
            // failing to open the mapped file.

            if (mappedFileHandle != IntPtr.Zero)
            { 
                safeMemorySectionHandle = new SafeViewOfFileHandle((IntPtr) pMemorySection, true);
                safeFileMappingHandle = new SafeFileMappingHandle(mappedFileHandle, true); 
            } 

            return pMemorySection; 
        }

        protected unsafe virtual String GetMemorySectionName()
        { 
            int iUseCodePage = this.bFlagDataTable ? dataTableCodePage : CodePage;
 
            String strName = String.Format(CultureInfo.InvariantCulture, "NLS_CodePage_{0}_{1}_{2}_{3}_{4}", 
                iUseCodePage, this.pCodePage->VersionMajor, this.pCodePage->VersionMinor,
                this.pCodePage->VersionRevision, this.pCodePage->VersionBuild); 

            return strName;
        }
 
        protected abstract unsafe void ReadBestFitTable();
 
        internal override char[] GetBestFitUnicodeToBytesData() 
        {
            // Read in our best fit table if necessary 
            if (arrayUnicodeBestFit == null) ReadBestFitTable();

            BCLDebug.Assert(arrayUnicodeBestFit != null,
                "[BaseCodePageEncoding.GetBestFitUnicodeToBytesData]Expected non-null arrayUnicodeBestFit"); 

            // Normally we don't have any best fit data. 
            return arrayUnicodeBestFit; 
        }
 
        internal override char[] GetBestFitBytesToUnicodeData()
        {
            // Read in our best fit table if necessary
            if (arrayUnicodeBestFit == null) ReadBestFitTable(); 

            BCLDebug.Assert(arrayBytesBestFit != null, 
                "[BaseCodePageEncoding.GetBestFitBytesToUnicodeData]Expected non-null arrayBytesBestFit"); 

            // Normally we don't have any best fit data. 
            return arrayBytesBestFit;
        }

        // During the AppDomain shutdown the Encoding class may already finalized and the memory section 
        // is invalid. so we detect that by validating the memory section handle then re-initialize the memory
        // section by calling LoadManagedCodePage() method and eventually the mapped file handle and 
        // the memory section pointer will get finalized one more time. 
        internal unsafe void CheckMemorySection()
        { 
            if (safeMemorySectionHandle != null && safeMemorySectionHandle.DangerousGetHandle() == IntPtr.Zero)
            {
                LoadManagedCodePage();
            } 
        }
    } 
} 


// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
                        

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