1 files changed, 192 insertions, 0 deletions
diff --git a/mfbt/IntegerRange.h b/mfbt/IntegerRange.h
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+++ b/mfbt/IntegerRange.h
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+/* -*- 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