Re: DT_GNU_HASH: ~ 50% dynamic linking improvement

["djamel anonymous" <djam8193ah at hotmail dot com>]

first thank you for replying to my post.

> I see absolutely no benefit at all in any of this.  The second hash
> table with the required second memory load would kill all the
> performance advantage.  It's sole purpose would be to not compare the
> chain list elements at all.  But:
>
> - it has to be pessimistic.  I.e., for the first table there are also
>   collisions and when they happen, the search must be made
in fact this second hash table is playing a role of a filter before the 
original table; a search
will be done into the original table if and only if the the corresponding 
bit is set in the new hash table .

> - each element in your second hash table must point to the beginning of
>   a chain.  So here the huge overhead in the hash table sizing is
>   costing a lot.  Furthermore, the division is nowadays no problem at
this new additional hash table will occupy on average nsymbols*8 bits which 
is nsymbols bytes; this is because we need only 1 bit per bucket; if this 
bit is set we continue the search into the original table otherwise the 
search is stopped after only one memory access and without doing actual 
division.

>   costing a lot.  Furthermore, the division is nowadays no problem at
>   all anymore.  It's fast.  If you really care, modify your linker to
>   size the hash table with a power of two and change the dynamic linker
>   to optimize that case.  It's easy enough to do.  The linker already
>   has a function to size the table more intelligently if requested.

the second hash table has in fact a smaller size than the original table, 
this is why its size is less important than the original one.the search into 
the original table will be done if and only if
the search into the new hash table is succesfull, and only then an actual 
division will be done to compute the bucket number into the original table 
.but this division will have much less impact on performance because it is 
done only in unlikely case of a succesfull search into the first hash table.
best reagrds.

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