mstl_hash.hpp

#pragma once

// weird hacky fix for hashes not working when passing to functions as an arg / etc. fuck you msvc
// always use this for your compile-time hashes.
#define HASH( str ) \
       []() { \
           constexpr hash_t ret = hash::fnv1a_ct( str ); \
           return ret; \
       }() \

using hash_t = uint32_t;

namespace hash {
    enum MagicNumbers : uint32_t {
        FNV1A_PRIME = 16777619u,
        FNV1A_BIAS = 2166136261u
    };

    // run-time FNV-1a hash.
    __forceinline hash_t fnv1a(const void *data, size_t len) {
        hash_t  out;
        uint8_t *enc;

        if (!data || !len)
            return hash_t{};

        // setup vars.
        out = FNV1A_BIAS;
        enc = (uint8_t *) data;

        // make hash.
        for (size_t i{}; i < len; ++i) {
            out ^= enc[i];
            out *= FNV1A_PRIME;
        }

        return out;
    }

    // run-time FNV-1a string hash.
    __forceinline hash_t fnv1a(const std::string &str) {
        return fnv1a(str.c_str(), str.length());
    }

    // compile-time FNV-1a string hash.
    constexpr hash_t fnv1a_ct(const char *str, hash_t start = FNV1A_BIAS) {
        return (*str != '\0') ? fnv1a_ct(str + 1, (*str ^ start) * FNV1A_PRIME) : start;
    }
};