To be honest I didn't time it and it wasn't thread safe and I don't have the source any more so I can't answer that. It doesn't do a lot so I imagine it would b

To be honest I didn't time it and it wasn't thread safe and I don't have the source any more so I can't answer that. It doesn't do a lot so I imagine it would be relatively cheap. The function it performed to rebuild the DFA was to create an NFA for the new pattern stream (it worked on char *) and then walk both the existing master NFA and the merge them. Then it was converted from NFA to DFA via dragon book copy and paste algorithm (my discrete math isn't great). Both NFA and DFA were represented as a bunch of C structs tied together by pointers. Then a table generator walked the new DFA and generated a new state table. It was very naive but covered the common case where large parts of the byte stream to be matched were similar. I've got MacVim up and writing it again. May post it as a Show HN if I get the time to finish it.