hashfn.hpp

/*
MIT License

Copyright (c) 2023 Max Goren - root@uniqueptr.com, www.maxgcoding.com

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
#ifndef hashfn_hpp
#define hashfn_hpp
#include <string>
#include <cstring>
using std::string;
using std::strlen;
using std::size_t;
using std::pair;
using std::make_pair;
//combined bernsteins hash with knuths cyclic shift
size_t __string_hash(const string& s) {
    unsigned long h = s.length();
    for (char c : s) {
        h = (h << 27) | (h >> 5);
        h = (33*h+int(c));
    }
    return h;
}

size_t __string_hash(char* str) {
    unsigned long h = strlen(str);
    for (int i = 0; str[i] != '\0'; i++) {
        h = (h << 27) | (h >> 5);
        h = (33 * h + int(str[i]));
    }
    return h;
}

template <typename K>
struct hashfn { };

template<> struct hashfn<string> {
    size_t operator()(string& s) {
        return __string_hash(s);
    }
};

template<> struct hashfn<const string> {
    size_t operator()(const string& s) {
        return __string_hash(s);
    }
};

template<> struct hashfn<char> {
    size_t operator()(char c) {
        return size_t(c);
    }
};

template<> struct hashfn<short> {
    size_t operator()(short c) {
        return size_t(c);
    }
};

template<> struct hashfn<int> {
    size_t operator()(int c) {
        return size_t(c);
    }
};

template<> struct hashfn<long> {
    size_t operator()(long c) {
        return size_t(c);
    }
};

template<> struct hashfn<unsigned char> {
    size_t operator()(unsigned char c) {
        return size_t(c);
    }
};

template<> struct hashfn<unsigned int> {
    size_t operator()(unsigned int c) {
        return size_t(c);
    }
};

template<> struct hashfn<unsigned short> {
    size_t operator()(unsigned short c) {
        return size_t(c);
    }
};

template<> struct hashfn<unsigned long> {
    size_t operator()(unsigned int c) {
        return size_t(c);
    }
};

template<> struct hashfn<unsigned long long> {
    size_t operator()(unsigned int c) {
        return size_t(c);
    }
};

#endif