Utils: Add SmallString

SmallString is a very simple utf8 string class. It's purpose is performance.
It uses a short string opimization which provides 31 bytes of heap free
memory to save a 30 bytes long string plus null terminator. If the string
gets larger heap is allocated. The grow strategy is 1.5 to improve reuse
of allocated memory.

It uses optionally constexpr to provide string literals.

Change-Id: I7757fb51abfeca200d074cbfce2f1d99edc0ecb0
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

1 files changed, 155 insertions, 0 deletions

diff --git a/src/libs/utils/smallstringiterator.h b/src/libs/utils/smallstringiterator.h
new file mode 100644
index 00000000000..d9425f21aa4
--- /dev/null
+++ b/src/libs/utils/smallstringiterator.h
@@ -0,0 +1,155 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <cstddef>
+#include <iterator>
+
+#pragma push_macro("noexcept")
+#ifndef __cpp_noexcept
+#define noexcept
+#endif
+
+namespace Utils {
+
+namespace Internal {
+
+template <class Category,
+          class Type,
+          typename DistanceType = ptrdiff_t,
+          typename Pointer = Type*,
+          typename Reference = Type&>
+struct SmallStringIterator : public  std::iterator<Category, Type, DistanceType, Pointer, Reference>
+{
+    SmallStringIterator() noexcept = default;
+
+    SmallStringIterator(Pointer ptr) : pointer_(ptr) noexcept
+    {
+    }
+
+    SmallStringIterator operator++() noexcept
+    {
+        return ++pointer_;
+    }
+    SmallStringIterator operator++(int) noexcept
+    {
+        return pointer_++;
+    }
+
+    SmallStringIterator operator--() noexcept
+    {
+        return --pointer_;
+    }
+
+    SmallStringIterator operator--(int) noexcept
+    {
+        return pointer_--;
+    }
+
+    SmallStringIterator operator+(DistanceType difference) const noexcept
+    {
+        return pointer_ + difference;
+    }
+
+    SmallStringIterator operator-(DistanceType difference) const noexcept
+    {
+        return pointer_ - difference;
+    }
+
+    SmallStringIterator operator+(std::size_t difference) const noexcept
+    {
+        return pointer_ + difference;
+    }
+
+    SmallStringIterator operator-(std::size_t difference) const noexcept
+    {
+        return pointer_ - difference;
+    }
+
+    DistanceType operator-(SmallStringIterator other) const noexcept
+    {
+        return pointer_ - other.data();
+    }
+
+    SmallStringIterator operator+=(DistanceType difference) noexcept
+    {
+        return pointer_ += difference;
+    }
+
+    SmallStringIterator operator-=(DistanceType difference) noexcept
+    {
+        return pointer_ -= difference;
+    }
+
+    Reference operator*() noexcept
+    {
+        return *pointer_;
+    }
+
+    const Reference operator*() const noexcept
+    {
+        return *pointer_;
+    }
+
+    Pointer operator->() noexcept
+    {
+        return pointer_;
+    }
+
+    const Pointer operator->() const noexcept
+    {
+        return pointer_;
+    }
+
+    bool operator==(SmallStringIterator other) const noexcept
+    {
+        return pointer_ == other.pointer_;
+    }
+
+    bool operator!=(SmallStringIterator other) const noexcept
+    {
+        return pointer_ != other.pointer_;
+    }
+
+    bool operator<(SmallStringIterator other) const noexcept
+    {
+        return pointer_ < other.pointer_;
+    }
+
+    Pointer data() noexcept
+    {
+        return pointer_;
+    }
+
+private:
+    Pointer pointer_ = nullptr;
+};
+
+} // namespace Internal
+
+} // namespace Utils
+
+#pragma pop_macro("noexcept")