Three Unlikely Successful Features of D

[H. S. Teoh]

On Tue, Mar 20, 2012 at 11:54:37PM -0600, Brad Anderson wrote:
[...]
> It's probably far too early to think about this with all the other
> important issues you're addressing but have you given much thought to
> improving the hashing function?  I haven't hit any issues with the
> speed of the current hasher but better performance is always welcome.
> MurmurHash seems to be all the rage these days with a lot of languages
> and systems adopting it <http://en.wikipedia.org/wiki/MurmurHash> (it
> compiles down to ~52 instructions on x86). It'd be interesting to see
> benchmarks with it.  I'm not sure where the current hashing function
> lives to see what it's like.
[...]

The current implementation actually has (at least) two different hash
functions:

- Paul Hsieh's SuperFastHash (rt.util.hash.hashOf)
- A custom hash for char[] and string: look in rt/typeinfo/ti_Ag.d for
  class TypeInfo_Aa, which has this:

        hash_t hash = 0;
        foreach (char c; s)
            hash = hash * 11 + c;

I'm going to benchmark both hash functions to see which is actually
faster. I suspect the custom hash is faster for small strings, though it
may not have good hash distribution.


T

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