System.Text.BaseCodePageEncoding.FindCodePage C# (CSharp) Method

        private unsafe bool FindCodePage(int codePage)
        {
            Debug.Assert(m_codePageHeader != null && m_codePageHeader.Length == CODEPAGE_HEADER_SIZE, "m_codePageHeader expected to match in size the struct CodePageHeader");

            // Loop through all of the m_pCodePageIndex[] items to find our code page
            byte[] codePageIndex = new byte[sizeof(CodePageIndex)];

            lock (s_streamLock)
            {
                // seek to the first CodePageIndex entry
                s_codePagesEncodingDataStream.Seek(CODEPAGE_DATA_FILE_HEADER_SIZE, SeekOrigin.Begin);

                int codePagesCount;
                fixed (byte* pBytes = s_codePagesDataHeader)
                {
                    CodePageDataFileHeader* pDataHeader = (CodePageDataFileHeader*)pBytes;
                    codePagesCount = pDataHeader->CodePageCount;
                }

                fixed (byte* pBytes = codePageIndex)
                {
                    CodePageIndex* pCodePageIndex = (CodePageIndex*)pBytes;
                    for (int i = 0; i < codePagesCount; i++)
                    {
                        s_codePagesEncodingDataStream.Read(codePageIndex, 0, codePageIndex.Length);

                        if (pCodePageIndex->CodePage == codePage)
                        {
                            // Found it!
                            long position = s_codePagesEncodingDataStream.Position;
                            s_codePagesEncodingDataStream.Seek((long)pCodePageIndex->Offset, SeekOrigin.Begin);
                            s_codePagesEncodingDataStream.Read(m_codePageHeader, 0, m_codePageHeader.Length);
                            m_firstDataWordOffset = (int)s_codePagesEncodingDataStream.Position; // stream now pointing to the codepage data

                            if (i == codePagesCount - 1) // last codepage
                            {
                                m_dataSize = (int)(s_codePagesEncodingDataStream.Length - pCodePageIndex->Offset - m_codePageHeader.Length);
                            }
                            else
                            {
                                // Read Next codepage data to get the offset and then calculate the size
                                s_codePagesEncodingDataStream.Seek(position, SeekOrigin.Begin);
                                int currentOffset = pCodePageIndex->Offset;
                                s_codePagesEncodingDataStream.Read(codePageIndex, 0, codePageIndex.Length);
                                m_dataSize = pCodePageIndex->Offset - currentOffset - m_codePageHeader.Length;
                            }

                            return true;
                        }
                    }
                }
            }

            // Couldn't find it
            return false;
        }

 internal unsafe static int GetCodePageByteSize(int codePage)
 {
     BaseCodePageEncoding.CodePageHeader *ptr = BaseCodePageEncoding.FindCodePage(codePage);
     if (ptr == null)
     {
         return(0);
     }
     return((int)ptr->ByteCount);
 }