public long AbsolutePosition()
{
// The number of bytes that the already-read characters need when encoded.
int numReadBytes = CurrentEncoding.GetByteCount(_charBuffer, 0, _charPos);
return(BaseStream.Position - _byteLen + numReadBytes);
}
public override int Read()
{
var ch = base.Read();
_position += CurrentEncoding.GetByteCount(new char[] { (char)ch });
return(ch);
}
public override string ReadLine()
{
string line = base.ReadLine();
if (line != null)
{
_position += CurrentEncoding.GetByteCount(line);
}
_position += CurrentEncoding.GetByteCount(Environment.NewLine);
return(line);
}
/// <summary>
/// Gets the actual position
/// </summary>
/// <returns></returns>
public long GetActualPosition()
{
//https://stackoverflow.com/questions/5404267/streamreader-and-seeking
var numBytesLeft = CurrentEncoding.GetByteCount(_charBuffer, _charPos, _charLen - _charPos);
// For variable-byte encodings, deal with partial chars at the end of the buffer
var numFragments = 0;
if (_byteLen <= 0 || CurrentEncoding.IsSingleByte)
{
return(BaseStream.Position - numBytesLeft - numFragments);
}
switch (CurrentEncoding.CodePage)
{
// UTF-8
case 65001:
{
byte byteCountMask = 0;
while (_byteBuffer[_byteLen - numFragments - 1] >> 6 == 2
) // if the byte is "10xx xxxx", it's a continuation-byte
{
byteCountMask |=
(byte)(1 << ++numFragments); // count bytes & build the "complete char" mask
}
if (_byteBuffer[_byteLen - numFragments - 1] >> 6 == 3
) // if the byte is "11xx xxxx", it starts a multi-byte char.
{
byteCountMask |=
(byte)(1 << ++numFragments); // count bytes & build the "complete char" mask
}
// see if we found as many bytes as the leading-byte says to expect
if (numFragments > 1 && _byteBuffer[_byteLen - numFragments] >> (7 - numFragments)
== byteCountMask)
{
numFragments = 0; // no partial-char in the byte-buffer to account for
}
break;
}
// UTF-16LE
case 1200:
{
if (_byteBuffer[_byteLen - 1] >= 0xd8) // high-surrogate
{
numFragments = 2; // account for the partial character
}
break;
}
// UTF-16BE
case 1201:
{
if (_byteBuffer[_byteLen - 2] >= 0xd8) // high-surrogate
{
numFragments = 2; // account for the partial character
}
break;
}
}
return(BaseStream.Position - numBytesLeft - numFragments);
}
