hash of mpz_t and mpq_t

[Hans Åberg]

> On 16 Jun 2021, at 22:54, Marco Bodrato <bodrato at mail.dm.unipi.it> wrote:
> 
> Ciao Hans,
> 
> Il 2021-06-16 22:29 Hans Åberg ha scritto:
>> namespace std {
>>  template<> struct hash<gmp::integer> {
>>    size_t operator()(gmp::integer const& x) const {
>>      std::size_t h = 0;
>>      for (mp_size_t i = 0; i < mpz_size(x.value_); ++i)
>>        h ^= std::hash<mp_limb_t>()(mpz_getlimbn(x.value_, i));
>>      return h ^ std::hash<mp_size_t>()(x.value_->_mp_size);
>>    }
>>  };
>> } // namespace std
> 
> A micro-optimisation: you can avoid an operation if you don't initialise h with 0.
> 
> namespace std {
>  template<> struct hash<gmp::integer> {
>    size_t operator()(gmp::integer const& x) const {
>      std::size_t h = std::hash<mp_size_t>()(x.value_->_mp_size);
>      for (mp_size_t i = 0; i < mpz_size(x.value_); ++i)
>        h ^= std::hash<mp_limb_t>()(mpz_getlimbn(x.value_, i));
>      return h;
>    }
>  };
> } // namespace std

Yes, that is better. Thanks!

But one still has to call _mp_size, underneath the API.