8 comments on “A brief tale of faster equality”

1. Stefan Wehr says:

   2010-10-19 at 08:35

   Hi Bryan,

   those numbers look very good! Thanks a lot!!

   Stefan

2. Johan Tibell says:

   2010-10-19 at 09:18

   This is great. Did you make similar changes to the Ord instance? It would matter a great deal in the common case of Map Text .

3. sfvisser says:

   2010-10-19 at 09:28

   Great news! Your library becomes faster without writing any code, my programs become faster without writing any code. Thanks a lot for this library.

4. Roman Leshchinskiy says:

   2010-10-19 at 15:17

   Did you find out what the performance problem in the stream fusion code was? I could bet it was mostly carrying two array indices instead of one. Also, did something like toUpper xs == toUpper ys get slower because of the change?

5. Bryan O'Sullivan says:

   2010-10-20 at 07:00

   Johan, I did Ord tonight, and it made a correspondingly large change to performance.

6. Bryan O'Sullivan says:

   2010-10-20 at 07:07

   Roman, I didn’t look for the source of the performance problem, but I doubt that it was caused by carrying two indices around. That’s what the compare implementation has to do, and it’s fast.

   As for your toUpper xs == toUpper ys question, that gets slower under GHC 7, but not 6. I’ve tried adding rewrite rules to catch these cases, but they’re not firing and I don’t know why.

   I have code that looks more or less like this:

   toLower :: Text -> Text
   toLower t = unstream (S.toLower (stream t))
   {-# INLINE toLower #-}

   oldCompare :: Text -> Text -> Ordering
   oldCompare a b = Stream.compare (stream a) (stream b)

   instance Ord Text where compare = oldCompare

   {-# RULES “TEXT compare fused” forall s1 s2.
   compare (unstream s1) (unstream s2) = Stream.compare s1 s2
   #-}

   That RULE doesn’t fire, and I don’t know why.

7. Roman Leshchinskiy says:

   2010-10-20 at 08:16

   Does adding {-# INLINE [1] compare #-} to the Ord instance help? Otherwise, compare could be inlined immediately, before the rule has had a chance to fire.

8. gwern says:

   2010-10-28 at 01:06

   This would have been more interesting with the code shown and differences explained. *What* 5-line change and why is it faster?

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1. teideal glic deisbhéalach » Blog Archive » text 0.10.0.0 is here says:

   2010-10-22 at 05:40

   […] Eq and Ord instances are also now very fast, up to 5x faster than before. They're now faster than the bytestring […]