calibre/src/perfect-hashing/frozen/string.h

/*
 * Frozen
 * Copyright 2016 QuarksLab
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

#ifndef FROZEN_LETITGO_STRING_H
#define FROZEN_LETITGO_STRING_H

#include "frozen/bits/elsa.h"
#include "frozen/bits/version.h"
#include "frozen/bits/defines.h"

#include <functional>

#ifdef FROZEN_LETITGO_HAS_STRING_VIEW
#include <string_view>
#endif

namespace frozen {

template <typename _CharT>
class basic_string {
  using chr_t = _CharT;

  chr_t const *data_;
  std::size_t size_;

public:
  template <std::size_t N>
  constexpr basic_string(chr_t const (&data)[N])
      : data_(data), size_(N - 1) {}
  constexpr basic_string(chr_t const *data, std::size_t size)
      : data_(data), size_(size) {}

#ifdef FROZEN_LETITGO_HAS_STRING_VIEW
  constexpr basic_string(std::basic_string_view<chr_t> data)
      : data_(data.data()), size_(data.size()) {}
#endif

  constexpr basic_string(const basic_string &) noexcept = default;
  constexpr basic_string &operator=(const basic_string &) noexcept = default;

  constexpr std::size_t size() const { return size_; }

  constexpr chr_t operator[](std::size_t i) const { return data_[i]; }

  constexpr bool operator==(basic_string other) const {
    if (size_ != other.size_)
      return false;
    for (std::size_t i = 0; i < size_; ++i)
      if (data_[i] != other.data_[i])
        return false;
    return true;
  }

  constexpr bool operator<(const basic_string &other) const {
    unsigned i = 0;
    while (i < size() && i < other.size()) {
      if ((*this)[i] < other[i]) {
        return true;
      }
      if ((*this)[i] > other[i]) {
        return false;
      }
      ++i;
    }
    return size() < other.size();
  }

  constexpr const chr_t *data() const { return data_; }
};

template <typename _CharT> struct elsa<basic_string<_CharT>> {
  constexpr std::size_t operator()(basic_string<_CharT> value) const {
    std::size_t d = 5381;
    for (std::size_t i = 0; i < value.size(); ++i)
      d = d * 33 + static_cast<size_t>(value[i]);
    return d;
  }
  // https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
  // With the lowest bits removed, based on experimental setup.
  constexpr std::size_t operator()(basic_string<_CharT> value, std::size_t seed) const {
    std::size_t d =  (0x811c9dc5 ^ seed) * static_cast<size_t>(0x01000193);
    for (std::size_t i = 0; i < value.size(); ++i)
      d = (d ^ static_cast<size_t>(value[i])) * static_cast<size_t>(0x01000193);
    return d >> 8 ;
  }
};

using string = basic_string<char>;
using wstring = basic_string<wchar_t>;
using u16string = basic_string<char16_t>;
using u32string = basic_string<char32_t>;

#ifdef FROZEN_LETITGO_HAS_CHAR8T
using u8string = basic_string<char8_t>;
#endif

namespace string_literals {

constexpr string operator"" _s(const char *data, std::size_t size) {
  return {data, size};
}

constexpr wstring operator"" _s(const wchar_t *data, std::size_t size) {
  return {data, size};
}

constexpr u16string operator"" _s(const char16_t *data, std::size_t size) {
  return {data, size};
}

constexpr u32string operator"" _s(const char32_t *data, std::size_t size) {
  return {data, size};
}

#ifdef FROZEN_LETITGO_HAS_CHAR8T
constexpr u8string operator"" _s(const char8_t *data, std::size_t size) {
  return {data, size};
}
#endif

} // namespace string_literals

} // namespace frozen

namespace std {
template <typename _CharT> struct hash<frozen::basic_string<_CharT>> {
  size_t operator()(frozen::basic_string<_CharT> s) const {
    return frozen::elsa<frozen::basic_string<_CharT>>{}(s);
  }
};
} // namespace std

#endif