compile time type hash

hash.cc

template <typename T>
constexpr uint64_t type_hash() {
    const char *name = __PRETTY_FUNCTION__;
    size_t len;
    for (len = 0; name[len]; len++);
    const uint64_t m = 0xc6a4a7935bd1e995ull;
    const int r = 47;
    const uint64_t seed = 0;
    uint64_t h = seed ^ (len * m);
    for (size_t j = 0; j < len / 8; ++j) {
        size_t i = j * 8;
        uint64_t k = ((uint64_t)(uint8_t)name[i]) | ((uint64_t)(uint8_t)name[i+1] << 8) |
            ((uint64_t)(uint8_t)name[i+2] << 16) | ((uint64_t)(uint8_t)name[i+3] << 24) |
            ((uint64_t)(uint8_t)name[i+4] << 32) | ((uint64_t)(uint8_t)name[i+5] << 40) |
            ((uint64_t)(uint8_t)name[i+6] << 48) | ((uint64_t)(uint8_t)name[i+7] << 56);
        k *= m;
        k ^= k >> r;
        k *= m;
        h ^= k;
        h *= m;
    }
    size_t i = len / 8 * 8;
    switch (len & 7) {
    case 7: h ^= ((uint64_t)(uint8_t)name[i+6]) << 48;
    case 6: h ^= ((uint64_t)(uint8_t)name[i+5]) << 40;
    case 5: h ^= ((uint64_t)(uint8_t)name[i+4]) << 32;
    case 4: h ^= ((uint64_t)(uint8_t)name[i+3]) << 24;
    case 3: h ^= ((uint64_t)(uint8_t)name[i+2]) << 16;
    case 2: h ^= ((uint64_t)(uint8_t)name[i+1]) << 8;
    case 1: h ^= ((uint64_t)(uint8_t)name[i+0]);
            h *= m;
    }
    h ^= h >> r;
    h *= m;
    h ^= h >> r;
    return h;
}