// postcondition: bufferedLength >= _currentIndex + min(readAhead, AmountLeft(_stream))
private void Buffer(int readAhead)
{
var readAheadTo = _currentIndex + readAhead;
if (readAheadTo >= _bufferedCount)
{
// we're about to read past the end of the current chunk. Pull a new chunk from the stream
var keepSeenLength = _bookmarks.Count > 0
? Location - _bookmarks[0]
: 0;
var keepFrom = _currentIndex - keepSeenLength;
var keepLength = _bufferedCount - keepFrom;
var amountToRead = Math.Max(_bufferChunkSize, readAheadTo - keepFrom);
var newBufferLength = _bufferedCount + amountToRead;
// _currentIndex
// |
// | _bufferedCount
// keepFrom | |
// | | | readAheadTo
// | | | |
// abcdefghijklmnopqrstuvwxyz
// readAhead |-----------|
// keepSeenLength |------|
// keepLength |-------------|
// amountToRead |----|
// newBufferLength |------------------|
for (var i = 0; i < keepFrom; i++)
{
_bufferStartSourcePos = _posCalculator(_buffer[i], _bufferStartSourcePos);
}
if (newBufferLength > _buffer.Length)
{
// grow the buffer
var newBuffer = ArrayPool <TToken> .Shared.Rent(Math.Max(newBufferLength, _buffer.Length * 2));
Array.Copy(_buffer, keepFrom, newBuffer, 0, keepLength);
ArrayPool <TToken> .Shared.Return(_buffer);
_buffer = newBuffer;
}
else if (keepFrom != 0 && keepLength != 0)
{
// move the buffer's contents to the start
// todo: find out how expensive this Copy tends to be.
// Could prevent it by using a ring buffer, but might make reads slower
Array.Copy(_buffer, keepFrom, _buffer, 0, keepLength);
}
_bufferStartLocation += keepFrom;
_currentIndex = keepSeenLength;
_bufferedCount = keepLength;
_bufferedCount += _stream.ReadInto(_buffer, _bufferedCount, amountToRead);
}
}