> I need dictionaries indexed by ints which must be very fast. I'm
> afraid that there is an overhead in using Hashtbl.t such that the
> generic hash function must recognize that the value is immediate
> instead of using it as a hash directly.
> 
> Is it worth to do something with it? What to do? I could copy the first
> half of hashtbl.ml and replace all occurrences of the function hash by
> land'ing with 0x3FFFFFFF (so the value is nonnegative and mod gives
> nonnegative results). Any better idea?

No, no need to copy anything, just unleash the power of functors!

module IntHashtbl = Hashtbl.make(struct type t = int
                                        let equal = (==)
                                        let hash x = x land 0x3FFFFFFF
                                 end)

I'm not sure the performance gain is significant, but it's worth a try.

- Xavier Leroy
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