context: /*
    Copyright (C) 2002, 2004, 2005 Jeroen Frijters
  
    This software is provided 'as-is', without any express or implied
    warranty.  In no event will the authors be held liable for any damages
    arising from the use of this software.
  
    Permission is granted to anyone to use this software for any purpose,
    including commercial applications, and to alter it and redistribute it
    freely, subject to the following restrictions:
  
    1. The origin of this software must not be misrepresented; you must not
       claim that you wrote the original software. If you use this software
       in a product, an acknowledgment in the product documentation would be
       appreciated but is not required.
    2. Altered source versions must be plainly marked as such, and must not be
       misrepresented as being the original software.
    3. This notice may not be removed or altered from any source distribution.
  
    Jeroen Frijters
    jeroen@frijters.net
    
  */
  using System;
  using System.IO;
  
  sealed class BigEndianBinaryReader
  {
  	private byte[] buf;
  	private int pos;
  	private int end;
  
  	internal BigEndianBinaryReader(byte[] buf, int offset, int length)
  	{
  		this.buf = buf;
  		this.pos = offset;
  		this.end = checked(offset + length);
  		if(offset < 0 || length < 0 || buf.Length - offset < length)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  	}
  
  	internal BigEndianBinaryReader Section(uint length)
  	{
  		BigEndianBinaryReader br = new BigEndianBinaryReader(buf, pos, checked((int)length));
  		Skip(length);
  		return br;
  	}
  
  	internal bool IsAtEnd
  	{
  		get
  		{
  			return pos == end;
  		}
  	}
  
  	internal int Position
  	{
  		get
  		{
  			return pos;
  		}
  	}
  
  	internal void Skip(uint count)
  	{
  		if(end - pos < count)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  		checked
  		{
  			pos += (int)count;
  		}
  	}
  
  	internal byte ReadByte()
  	{
  		if(pos == end)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  		return buf[pos++];
  	}
  
  	internal sbyte ReadSByte()
  	{
  		if(pos == end)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  		return (sbyte)buf[pos++];
  	}
  
  	internal double ReadDouble()
  	{
  		return BitConverter.Int64BitsToDouble(ReadInt64());
  	}
  
  	internal short ReadInt16()
  	{
  		if(end - pos < 2)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  		short s = (short)((buf[pos] << 8) + buf[pos + 1]);
  		pos += 2;
  		return s;
  	}
  
  	internal int ReadInt32()
  	{
  		if(end - pos < 4)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  		int i = (int)((buf[pos] << 24) + (buf[pos + 1] << 16) + (buf[pos + 2] << 8) + buf[pos + 3]);
  		pos += 4;
  		return i;
  	}
  
  	internal long ReadInt64()
  	{
  		if(end - pos < 8)
  		{
  			throw new ClassFormatError("Truncated class file");
  		}
  		uint i1 = (uint)((buf[pos] << 24) + (buf[pos + 1] << 16) + (buf[pos + 2] << 8) + buf[pos + 3]);
  		uint i2 = (uint)((buf[pos + 4] << 24) + (buf[pos + 5] << 16) + (buf[pos + 6] << 8) + buf[pos + 7]);
  		long l = (((long)i1) << 32) + i2;
  		pos += 8;
  		return l;
  	}
  
  	internal float ReadSingle()
  	{
  		return BitConverter.ToSingle(BitConverter.GetBytes(ReadInt32()), 0);
  	}
  
  	internal string ReadString(string classFile)
  	{
  		int len = ReadUInt16();
  		if(end - pos < len)
  		{
  			throw new ClassFormatError("{0} (Truncated class file)", classFile);
  		}
  		// special code path for ASCII strings (which occur *very* frequently)
  		for(int j = 0; j < len; j++)
  		{
  			if(buf[pos + j] == 0 || buf[pos + j] >= 128)
  			{
  				// NOTE we *cannot* use System.Text.UTF8Encoding, because this is *not* compatible
  				// (esp. for embedded nulls)
  				char[] ch = new char[len];
  				int l = 0;
  				for(int i = 0; i < len; i++)
  				{
  					int c = buf[pos + i];
  					int char2, char3;
  					switch (c >> 4)
  					{
  						case 0:
  							if(c == 0)
  							{
  								throw new ClassFormatError("{0} (Illegal UTF8 string in constant pool)", classFile);
  							}
  							break;
  						case 1: case 2: case 3: case 4: case 5: case 6: case 7:
  							// 0xxxxxxx
  							break;
  						case 12: case 13:
  							// 110x xxxx   10xx xxxx
  							char2 = buf[pos + ++i];
  							if((char2 & 0xc0) != 0x80)
  							{
  								throw new ClassFormatError("{0} (Illegal UTF8 string in constant pool)", classFile);
  							}
  							c = (((c & 0x1F) << 6) | (char2 & 0x3F));
  							break;
  						case 14:
  							// 1110 xxxx  10xx xxxx  10xx xxxx
  							char2 = buf[pos + ++i];
  							char3 = buf[pos + ++i];
  							if((char2 & 0xc0) != 0x80 || (char3 & 0xc0) != 0x80)
  							{
  								throw new ClassFormatError("{0} (Illegal UTF8 string in constant pool)", classFile);
  							}
  							c = (((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0));
  							break;
  						default:
  							throw new ClassFormatError("{0} (Illegal UTF8 string in constant pool)", classFile);
  					}
  					ch[l++] = (char)c;
  				}
  				pos += len;
  				return new String(ch, 0, l);
  			}
  		}
  		string s = System.Text.ASCIIEncoding.ASCII.GetString(buf, pos, len);
  		pos += len;
  		return s;
  	}
  
  	internal ushort ReadUInt16()
  	{
  
gt: 		if(end - pos < 2)