Add CheckedRange<> and its test

util/numeric/checked_range.h

Index: util/numeric/checked_range.h
diff --git a/util/numeric/checked_range.h b/util/numeric/checked_range.h
new file mode 100644
index 0000000000000000000000000000000000000000..83e87d20e422260255e6602cd7fb3528beeaf4df
--- /dev/null
+++ b/util/numeric/checked_range.h
@@ -0,0 +1,116 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed 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 CRASHPAD_UTIL_NUMERIC_CHECKED_RANGE_H_
+#define CRASHPAD_UTIL_NUMERIC_CHECKED_RANGE_H_
+
+#include <limits>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/numerics/safe_conversions.h"
+#include "base/numerics/safe_math.h"
+
+namespace crashpad {
+
+//! \brief Ensures that a range, composed of a base and size, does not overflow
+//!     its data type.
+template <typename ValueType, typename SizeType = ValueType>
+class CheckedRange {
+ public:
+  CheckedRange(ValueType base, SizeType size) {
+    COMPILE_ASSERT(!std::numeric_limits<SizeType>::is_signed,
+                   SizeType_must_be_unsigned);
+    SetRange(base, size);
+  }
+
+  //! \brief Sets the range’s base and size to \a base and \a size,
+  //!     respectively.
+  void SetRange(ValueType base, SizeType size) {
+    base_ = base;
+    size_ = size;
+  }
+
+  //! \brief The range’s base.
+  ValueType base() const { return base_; }
+
+  //! \brief The range’s size.
+  SizeType size() const { return size_; }
+
+  //! \brief The range’s end, its base plus its size.
+  ValueType end() const { return base_ + size_; }
+
+  //! \brief Returns the validity of the range.
+  //!
+  //! \return `true` if the range is valid, `false` otherwise.
+  //!
+  //! A range is valid if its size can be converted to the range’s data type
+  //! without data loss, and if its end (base plus size) can be computed without
+  //! overflowing its data type.
+  bool IsValid() const {
+    base::CheckedNumeric<ValueType> checked_base_(base_);

[Robert Sesek, 2014/08/14 20:55:52]

No underscore at the end of checked_base_, or on line 66.

+    if (!base::IsValueInRangeForNumericType<ValueType, SizeType>(size_)) {
+      return false;
+    }
+    base::CheckedNumeric<ValueType> checked_end_(checked_base_ +
+                                                 static_cast<ValueType>(size_));

[Robert Sesek, 2014/08/14 20:55:52]

This read "fishy" for me for me, so I spent 10 minutes looking at this line. I
think you can more succinctly write this function, and have it read safer, as:

  bool IsValid() const {
    if (!base::IsValueInRangeForNumericType<ValueType, SizeType>(size_)) {
      return false;
    }
    base::CheckedNumeric<ValueType> checked_end(base_);
    checked_end += static_cast<ValueType>(size_);
    return checked_end.IsValid();
  }

[Mark Mentovai, 2014/08/14 23:12:01]

rsesek wrote:
Yup, that’s better!

+    return checked_end_.IsValid();
+  }
+
+  //! \brief Returns whether the range contains another value.
+  //!
+  //! \param[in] value The (possibly) contained value.
+  //!
+  //! \return `true` if the range contains \a value, `false` otherwise.
+  //!
+  //! A range contains a value if the value is greater than or equal to its
+  //! base, and less than its end (base plus size).
+  //!
+  //! This method must only be called if IsValid() would return `true`.
+  bool ContainsValue(ValueType value) const {
+    DCHECK(IsValid());
+
+    return value >= base_ && value < end();

[Robert Sesek, 2014/08/14 20:55:52]

Why base_ but end() ?

+  }
+
+  //! \brief Returns whether the range contains another range.
+  //!
+  //! \param[in] that The (possibly) contained range.
+  //!
+  //! \return `true` if `this` range, the containing range, contains \a that,
+  //!     the contained range. `false` otherwise.
+  //!
+  //! A range contains another range when the contained range’s base is greater
+  //! than or equal to the containing range’s base, and the contained range’s
+  //! end is less than or equal to the containing range’s end.
+  //!
+  //! This method must only be called if IsValid() would return `true` for both
+  //! CheckedRange objects involved.
+  bool ContainsRange(const CheckedRange<ValueType, SizeType>& that) const {
+    DCHECK(IsValid());
+    DCHECK(that.IsValid());
+
+    return that.base_ >= base_ && that.end() <= end();

[Robert Sesek, 2014/08/14 20:55:52]

Same.

+  }
+
+ private:
+  ValueType base_;
+  SizeType size_;
+
+  DISALLOW_COPY_AND_ASSIGN(CheckedRange);
+};
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_NUMERIC_CHECKED_RANGE_H_