[Haskell-cafe] FPS lib

Donald Bruce Stewart dons at cse.unsw.edu.au
Tue Oct 18 20:07:37 EDT 2005

> Hello Guys,
> I tried my own version of PackedStrings and the results are very nice.
> It is entirely based on ByteArray# and Int#. I have made two tests:
> Elapsed time
> |     | FastPackedString | PackedString |
> +-----+------------------+--------------+
> |test1|           99.26s |        3.81s |
> |test2|          175.88s |        5.28s |
> Maximum Memory Residency
> |     | FastPackedString | PackedString |
> +-----+------------------+--------------+
> |test1|          40.60Mb |      36.25Mb |
> |test2|          91.58Mb |      33.94Mb |

Wow. Now this is really surprising. 

Firstly, I would point out that only testing pack and concat may be
slightly unrepresentative :)

However, on my machine:

    OpenBSD/Pentium-M 1.6G/ghc-6.5 -O
    Elapsed time:        FPS          Simon's PackedString   Krasimir's
    test1                1.966s (40M)      2.151s (36M)      2.235s (36M)
    test2                6.048s (24M)      3.160s (73M)      2.318s (39M)

Which is basically what I expected. Though perhaps I need to improve
concat (we currently do things a little strangely in concat, due to the
darcs legacy), but pack itself is nice and fast.

    Linux/Pentium 4 3.6G/ghc-6.4.1 -O
    test1               35.37s            30.97s             2.180s
    test2               90.93s            60.55s             1.916s

Ah!! So what's going on on Linux, I wonder. Could it be something about
6.4.1? Are we seeing the difference between ForeignPtrs from 6.4 to 6.5?
I will investigate.

I'd be very wary of switching entirely to non-portable ghc primop-based
code, as FPS already run ons hugs and I think nhc.

-- Don

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