hash of mpz_t and mpq_t

Marco Bodrato bodrato at mail.dm.unipi.it
Tue Jun 15 16:44:42 UTC 2021


Il 2021-06-15 14:56 Hans Åberg ha scritto:
>     size_t operator()(gmp::integer const& x) const {
>       std::size_t h = 0;
>       for (int i = 0; i < abs(x.value_->_mp_size); ++i)
>         h ^= std::hash<mp_limb_t>()(x.value_->_mp_d[i]);
>       return h;
>     }

> Possibly, it may not be stable because of calling GMP internals, so
> there might be a point in adding that.

I'd suggest to look at 
https://gmplib.org/manual/Integer-Special-Functions ,
looking in particular for mpz_size and mpz_getlimbn ;-) (or even 
I'm sure that the same function can be rewritten using only documented 
access to the GMP types :-P

You may also look at 
https://gmplib.org/manual/C_002b_002b-Interface-General ,
in particular the function mpz_t mpz_class::get_mpz_t (), if you want to 
use the mpz_class in C++.

Anyway, the features that different users may ask for a "hash" function 
are very different...


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