hashing.h

// =====================================================================================================================
//  fennec, a free and open source game engine
//  Copyright © 2025  Medusa Slockbower
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
// =====================================================================================================================
 
#ifndef FENNEC_LANG_HASHING_H
#define FENNEC_LANG_HASHING_H
 
#include <fennec/lang/types.h>
#include <fennec/lang/type_traits.h>
#include <fennec/lang/bits.h>
 
namespace fennec
{
 
template<typename Key> struct hash;
 
// Murmur3 Hash for 64-bit ints
template<>
struct hash<uint64_t> {
    using type_t = uint64_t;
    constexpr size_t operator()(uint64_t x) const {
        // Murmur3
        x ^= x >> 33U;
        x *= 0xff51afd7ed558ccd;
        x ^= x >> 33U;
        x *= 0xc4ceb9fe1a85ec53;
        x ^= x >> 33U;
        return x;
    }
};
 
// Wrapper for casting ints
template<typename IntT>
    requires is_integral_v<IntT>
struct hash<IntT> : hash<uint64_t> {
    using type_t = IntT;
};
 
// Wrapper for pointers
template<typename PtrT>
struct hash<PtrT*> : hash<uintptr_t> {
    constexpr size_t operator()(PtrT* ptr) const {
        return hash<uintptr_t>::operator()((uintptr_t)(const void*)ptr);
    }
};
 
// Float
template<>
struct hash<float> : hash<uint32_t> {
    constexpr size_t operator()(float x) const {
        return hash<uint32_t>::operator()(bit_cast<uint32_t>(x));
    }
};
 
template<>
struct hash<double> : hash<uint64_t> {
    constexpr size_t operator()(double x) const {
        return hash<uint64_t>::operator()(bit_cast<uint64_t>(x));
    }
};
 
 
constexpr size_t pair_hash(size_t x, size_t y) {
    // Szudzik Pairing
    return (x >= y ? (x * x) + x + y : (y * y) + x);
}
 
}
 
#endif // FENNEC_LANG_HASHING_H