Re: Good hash for pointers

Am 23.05.2024 um 13:11 schrieb Malcolm McLean:

 What is a good hash function for pointers to use in portable ANSI C?
 The pointers are nodes of a tree, which are read only, and I want to associate read/write data with them. So potentially a lage number of pointers,and they might be consecutively ordered if they are taken from an array, or they might be returned from repeared calls to malloc() with small allocations. Obviously I have no control over pointer size or internal representation.
 

That's what std::hash<void *> maps to on libstdc++:
  template<typename _Tp>
    struct hash<_Tp*> : public __hash_base<size_t, _Tp*>
    {
      size_t
      operator()(_Tp* __p) const noexcept
      { return reinterpret_cast<size_t>(__p); }
    };
So if libstdc++ directly casts the pointer to a size_t ... ;-)