IntegerRange.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Iterator over ranges of integers */

#ifndef mozilla_IntegerRange_h
#define mozilla_IntegerRange_h

#include "mozilla/Assertions.h"
#include "mozilla/ReverseIterator.h"

#include <iterator>
#include <type_traits>

namespace mozilla {

namespace detail {

template <typename IntTypeT>
class IntegerIterator {
 public:
  // It is disputable whether these type definitions are correct, since
  // operator* doesn't return a reference at all. Also, the iterator_category
  // can be at most std::input_iterator_tag (rather than
  // std::bidrectional_iterator_tag, as it might seem), because it is a stashing
  // iterator. See also, e.g.,
  // https://stackoverflow.com/questions/50909701/what-should-be-iterator-category-for-a-stashing-iterator
  using value_type = const IntTypeT;
  using pointer = const value_type*;
  using reference = const value_type&;
  using difference_type = std::make_signed_t<IntTypeT>;
  using iterator_category = std::input_iterator_tag;

  template <typename IntType>
  explicit IntegerIterator(IntType aCurrent) : mCurrent(aCurrent) {}

  template <typename IntType>
  explicit IntegerIterator(const IntegerIterator<IntType>& aOther)
      : mCurrent(aOther.mCurrent) {}

  // This intentionally returns a value rather than a reference, to make
  // mozilla::ReverseIterator work with it. Still, std::reverse_iterator cannot
  // be used with IntegerIterator because it still is a "stashing iterator". See
  // Bug 1175485.
  IntTypeT operator*() const { return mCurrent; }

  /* Increment and decrement operators */

  IntegerIterator& operator++() {
    ++mCurrent;
    return *this;
  }
  IntegerIterator& operator--() {
    --mCurrent;
    return *this;
  }
  IntegerIterator operator++(int) {
    auto ret = *this;
    ++mCurrent;
    return ret;
  }
  IntegerIterator operator--(int) {
    auto ret = *this;
    --mCurrent;
    return ret;
  }

  /* Comparison operators */

  template <typename IntType1, typename IntType2>
  friend bool operator==(const IntegerIterator<IntType1>& aIter1,
                         const IntegerIterator<IntType2>& aIter2);
  template <typename IntType1, typename IntType2>
  friend bool operator!=(const IntegerIterator<IntType1>& aIter1,
                         const IntegerIterator<IntType2>& aIter2);
  template <typename IntType1, typename IntType2>
  friend bool operator<(const IntegerIterator<IntType1>& aIter1,
                        const IntegerIterator<IntType2>& aIter2);
  template <typename IntType1, typename IntType2>
  friend bool operator<=(const IntegerIterator<IntType1>& aIter1,
                         const IntegerIterator<IntType2>& aIter2);
  template <typename IntType1, typename IntType2>
  friend bool operator>(const IntegerIterator<IntType1>& aIter1,
                        const IntegerIterator<IntType2>& aIter2);
  template <typename IntType1, typename IntType2>
  friend bool operator>=(const IntegerIterator<IntType1>& aIter1,
                         const IntegerIterator<IntType2>& aIter2);

 private:
  IntTypeT mCurrent;
};

template <typename IntType1, typename IntType2>
bool operator==(const IntegerIterator<IntType1>& aIter1,
                const IntegerIterator<IntType2>& aIter2) {
  return aIter1.mCurrent == aIter2.mCurrent;
}

template <typename IntType1, typename IntType2>
bool operator!=(const IntegerIterator<IntType1>& aIter1,
                const IntegerIterator<IntType2>& aIter2) {
  return aIter1.mCurrent != aIter2.mCurrent;
}

template <typename IntType1, typename IntType2>
bool operator<(const IntegerIterator<IntType1>& aIter1,
               const IntegerIterator<IntType2>& aIter2) {
  return aIter1.mCurrent < aIter2.mCurrent;
}

template <typename IntType1, typename IntType2>
bool operator<=(const IntegerIterator<IntType1>& aIter1,
                const IntegerIterator<IntType2>& aIter2) {
  return aIter1.mCurrent <= aIter2.mCurrent;
}

template <typename IntType1, typename IntType2>
bool operator>(const IntegerIterator<IntType1>& aIter1,
               const IntegerIterator<IntType2>& aIter2) {
  return aIter1.mCurrent > aIter2.mCurrent;
}

template <typename IntType1, typename IntType2>
bool operator>=(const IntegerIterator<IntType1>& aIter1,
                const IntegerIterator<IntType2>& aIter2) {
  return aIter1.mCurrent >= aIter2.mCurrent;
}

template <typename IntTypeT>
class IntegerRange {
 public:
  typedef IntegerIterator<IntTypeT> iterator;
  typedef IntegerIterator<IntTypeT> const_iterator;
  typedef ReverseIterator<IntegerIterator<IntTypeT>> reverse_iterator;
  typedef ReverseIterator<IntegerIterator<IntTypeT>> const_reverse_iterator;

  template <typename IntType>
  explicit IntegerRange(IntType aEnd) : mBegin(0), mEnd(aEnd) {}

  template <typename IntType1, typename IntType2>
  IntegerRange(IntType1 aBegin, IntType2 aEnd) : mBegin(aBegin), mEnd(aEnd) {}

  iterator begin() const { return iterator(mBegin); }
  const_iterator cbegin() const { return begin(); }
  iterator end() const { return iterator(mEnd); }
  const_iterator cend() const { return end(); }
  reverse_iterator rbegin() const { return reverse_iterator(iterator(mEnd)); }
  const_reverse_iterator crbegin() const { return rbegin(); }
  reverse_iterator rend() const { return reverse_iterator(iterator(mBegin)); }
  const_reverse_iterator crend() const { return rend(); }

 private:
  IntTypeT mBegin;
  IntTypeT mEnd;
};

template <typename T, bool = std::is_unsigned_v<T>>
struct GeqZero {
  static bool isNonNegative(T t) { return t >= 0; }
};

template <typename T>
struct GeqZero<T, true> {
  static bool isNonNegative(T t) { return true; }
};

}  // namespace detail

template <typename IntType>
detail::IntegerRange<IntType> IntegerRange(IntType aEnd) {
  static_assert(std::is_integral_v<IntType>, "value must be integral");
  MOZ_ASSERT(detail::GeqZero<IntType>::isNonNegative(aEnd),
             "Should never have negative value here");
  return detail::IntegerRange<IntType>(aEnd);
}

template <typename IntType1, typename IntType2>
detail::IntegerRange<IntType2> IntegerRange(IntType1 aBegin, IntType2 aEnd) {
  static_assert(std::is_integral_v<IntType1> && std::is_integral_v<IntType2>,
                "values must both be integral");
  static_assert(std::is_signed_v<IntType1> == std::is_signed_v<IntType2>,
                "signed/unsigned mismatch");
  MOZ_ASSERT(aEnd >= aBegin, "End value should be larger than begin value");
  return detail::IntegerRange<IntType2>(aBegin, aEnd);
}

}  // namespace mozilla

#endif  // mozilla_IntegerRange_h