writeBackReference method

@override void writeBackReference(int distance, int count)

Append count bytes copied from distance bytes before the current end of the stream (an LZ77 back-reference, as used by Inflate). Correctly handles overlapping copies where count > distance (e.g. RLE-style runs), reproducing the repeating pattern.

This default implementation is expressed in terms of subset and writeBytes; subclasses backed by a contiguous buffer should override it with a direct in-buffer copy to avoid per-iteration view allocations.

Implementation

@override
void writeBackReference(int distance, int count) {
  while (length + count > _buffer.length) {
    _expandBuffer((length + count) - _buffer.length);
  }
  final src = length - distance;
  if (distance >= count) {
    // Non-overlapping copy: bulk move is safe and fast.
    _buffer.setRange(length, length + count, _buffer, src);
  } else {
    // Overlapping copy (LZ77 run): copy forward byte-by-byte so the source
    // bytes written earlier in this same call are repeated correctly.
    var s = src;
    var d = length;
    final end = length + count;
    while (d < end) {
      _buffer[d++] = _buffer[s++];
    }
  }
  length += count;
}