def _data_in_prefetch_buffers(self, offset):
k = [i for i in self._prefetch_data.keys() if i <= offset]<EOL>if len(k) == <NUM_LIT:0>:<EOL><INDENT>return None<EOL><DEDENT>index = max(k)<EOL>buf_offset = offset - index<EOL>if buf_offset >= len(self._prefetch_data[index]):<EOL><INDENT>return None<EOL><DEDENT>return index<EOL>
if a block of data is present in the prefetch buffers, at the given
offset, return the offset of the relevant prefetch buffer.  otherwise,
return None.  this guarantees nothing about the number of bytes
collected in the prefetch buffer so far.