std::hash for __uint128_t

Question

I am facing an issue hashing __uint128_t. Following is my code:

#include <iostream> int main () { __uint128_t var = 1; std::cout << std::hash<__uint128_t> () (var) << "\n"; return 0; }

I am getting the error as:

test.cpp: In function ‘int main()’: test.cpp:5:40: error: use of deleted function ‘std::hash<__int128 unsigned>::hash()’ 5 | size_t h = std::hash<__uint128_t> () (var); | ^

How can I get the hash for __uint128_t? (Probably a very basic question but I have been stuck here for a while). Also, I would like to know the meaning of the error. Thanks in advance.

You can separate it into two 64-bit values and combine their hashes. — interjay
– interjay, Commented Apr 3, 2021 at 12:38
__uint128_t is not a standard type so std::hash is not required to support it. — interjay
– interjay, Commented Apr 3, 2021 at 14:52

ceorron · Accepted Answer · 2021-04-03 12:38:08Z

Taking a look at the docs on https://en.cppreference.com/w/cpp/utility/hash. You will have to write your own.

Here is some code for what a basic __uint128_t hash function might look like:

namespace std { template<> struct hash<__uint128_t> { size_t operator()(__uint128_t var) const { return std::hash<uint64_t>{}((uint64_t)var ^ (uint64_t)(var >> 64)); } }; }

Note not tested or compiled.

Plus one. Could you further include the referenced hash_combine function instead of a simple xor?

Collectives™ on Stack Overflow

std::hash for __uint128_t

1 Answer 1

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Linked

Related