ByteArrayRawHasher改进建议

[ZikangYuan]

目前的开源版本代码没有实现移动构造函数和移动赋值运算符。std::unordered_map 在内部（例如 rehash 时）会大量移动元素。没有移动语义，它会回退到（更慢的）拷贝操作，导致不必要的内存分配和复制。在最坏的情况下，不正确的隐式移动可能导致双重释放（double-free）错误。

建议修改成下述表达以避免隐患：

struct ByteArrayRaw {
    std::vector<uint8_t> data;
    static size_t size; 

    ByteArrayRaw() : data(size) {}

    bool operator==(const ByteArrayRaw &other) const {
        return data == other.data;
    }
};

struct ByteArrayRawHasher {
  size_t operator()(const ByteArrayRaw &arr) const {
    const size_t dataSize = arr.data.size();
    const uint8_t* raw_data = arr.data.data();

    const uint64_t seed = 0xc3a5c85c97cb3127ULL;
    const uint64_t m = 0xc6a4a7935bd1e995ULL;
    const int r = 47;

    size_t h = seed ^ (dataSize * m);

    const uint64_t *data = reinterpret_cast<const uint64_t *>(raw_data);
    const uint64_t *end = data + (dataSize / 8);

    while (data != end) {
        uint64_t k = *data++;
        k *= m; k ^= k >> r; k *= m;
        h ^= k; h *= m;
    }

    const unsigned char *tail = reinterpret_cast<const unsigned char *>(data);

    switch (dataSize & 7) {
    case 7: h ^= uint64_t(tail[6]) << 48;
    case 6: h ^= uint64_t(tail[5]) << 40;
    case 5: h ^= uint64_t(tail[4]) << 32;
    case 4: h ^= uint64_t(tail[3]) << 24;
    case 3: h ^= uint64_t(tail[2]) << 16;
    case 2: h ^= uint64_t(tail[1]) << 8;
    case 1: h ^= uint64_t(tail[0]); h *= m;
    }

    h ^= h >> r; h *= m; h ^= h >> r;
    return h;
  }
};

因为std::vector实现了移动语义