# Hashing and Checksums

> StringZilla for C++

In C++, hashing is exposed as methods — `view.hash(seed = 0)`, `view.bytesum()`, and `view.hash_multiseed(seeds, hashes)` — and as the function object `sz::hash{}` together with `sz::equal_to{}`, which are convenient as template arguments for `std::unordered_map`/`std::unordered_set`.
`sz::fill_random(slice, nonce)` fills a mutable span with reproducible noise.

```cpp
#include <stringzilla/stringzilla.hpp>
#include <unordered_map>
#include <unordered_set>
#include <cassert>
namespace sz = ashvardanian::stringzilla;

int main() {
    // Drop the SIMD hash and equality into the STL containers as template arguments.
    std::unordered_map<std::string, int, sz::hash, sz::equal_to> counts;
    for (char const *word : {"apple", "banana", "apple"}) counts[word] += 1;
    assert(counts["apple"] == 2);
    assert(counts.size() == 2);

    // `sz::string_t` keys also work in the plain containers, via the bundled `std::hash` specialization.
    std::unordered_set<sz::string_t> uniq = {"apple", "banana"};
    assert(uniq.count("apple") == 1);

    sz::string_t noise(16, '\0');
    sz::fill_random(noise.span(), /*nonce*/ 7); // reproducible noise
    assert(noise.size() == 16);
    return 0;
}
```

`#include <stringzilla/stringzilla.hpp>`

## hash

Helper function-like object to hash string-view convertible objects with StringZilla.

```cpp
struct hash
```

Similar to `std::hash<std::string_view>`, but doesn't require including the heavy `<functional>` header. Can be used to combine STL classes with StringZilla logic, like: `std::unordered_map<std::string, int, sz::hash, sz::equal_to>`.

See also: std::hash: [https://en.cppreference.com/w/cpp/utility/functional/hash](https://en.cppreference.com/w/cpp/utility/functional/hash)