Commits on Apr 22, 2016

1. More improvements to the DFA's inner loop. …

   There were two important changes:
   
     1. self.at is used sparingly in favor of a local `let at` binding.
        This seems to convince the compiler to use a register.
     2. Switch the transition table from a `Vec<Box<[StatePtr]>>` to a
        row-major `Vec<StatePtr>`.
   
   (2) is the juicier of the two. It makes more efficient use of the cache.
   In particular, a critical aspect is that a StatePtr points to the start
   of a row in the table, which enables indexing in the inner loop with a
   single ADD instruction. (i.e., `si + byte` instead of
   `si * #classes + byte`.)

   

   BurntSushi committed Apr 22, 2016
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