tr1::hashtable::operator[]

[Paolo Carlini]

Paolo Carlini wrote:

> Joe Buck wrote:
>
>> There is wasted work because of the two lookups, but perhaps there's
>> a way to further improve the situation by exposing the common part
>> of find() and insert(), namely the hash computation.  If there were
>> a way to do the find(), and somehow reuse the hash computed by the
>> find() to do the insert() more quickly, then I think Peter's approach
>> would be an even bigger win.
>
> Definitely. That is exactly my point.

... and the below is a preview of my implementation of your (Joe's and 
Peter's) very helpful suggestions. As you can see, in a nutshell the 
idea is implementing insert with hint and calling it from operator[] (as 
per our std::map). In this case the hint is "special", we are not 
passing a regular iterator, because we have to convey somehow the info 
that the element is not present yet and in which bucket it will be 
inserted (assuming no rehashing occurs).

As-is the patch (*) already passes regtesting and a few additional 
simple tests, it would be nice if Peter could benchmark it, while I 
refine it to its final (hoepfully cleaner) shape...

Thanks,
Paolo.

(*) It includes trivial clean-ups, otherwise would be much smaller.

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