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diff --git a/mfbt/Char16.h b/mfbt/Char16.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/. */
+
+/* Implements a UTF-16 character type. */
+
+#ifndef mozilla_Char16_h
+#define mozilla_Char16_h
+
+#ifdef __cplusplus
+
+/*
+ * C++11 introduces a char16_t type and support for UTF-16 string and character
+ * literals. C++11's char16_t is a distinct builtin type. Technically, char16_t
+ * is a 16-bit code unit of a Unicode code point, not a "character".
+ */
+
+#ifdef WIN32
+# define MOZ_USE_CHAR16_WRAPPER
+# include <cstdint>
+ /**
+ * Win32 API extensively uses wchar_t, which is represented by a separated
+ * builtin type than char16_t per spec. It's not the case for MSVC prior to
+ * MSVC 2015, but other compilers follow the spec. We want to mix wchar_t and
+ * char16_t on Windows builds. This class is supposed to make it easier. It
+ * stores char16_t const pointer, but provides implicit casts for wchar_t as
+ * well. On other platforms, we simply use
+ * |typedef const char16_t* char16ptr_t|. Here, we want to make the class as
+ * similar to this typedef, including providing some casts that are allowed
+ * by the typedef.
+ */
+class char16ptr_t
+{
+private:
+ const char16_t* mPtr;
+ static_assert(sizeof(char16_t) == sizeof(wchar_t),
+ "char16_t and wchar_t sizes differ");
+
+public:
+ char16ptr_t(const char16_t* aPtr) : mPtr(aPtr) {}
+ char16ptr_t(const wchar_t* aPtr) :
+ mPtr(reinterpret_cast<const char16_t*>(aPtr))
+ {}
+
+ /* Without this, nullptr assignment would be ambiguous. */
+ constexpr char16ptr_t(decltype(nullptr)) : mPtr(nullptr) {}
+
+ operator const char16_t*() const
+ {
+ return mPtr;
+ }
+ operator const wchar_t*() const
+ {
+ return reinterpret_cast<const wchar_t*>(mPtr);
+ }
+ operator const void*() const
+ {
+ return mPtr;
+ }
+ operator bool() const
+ {
+ return mPtr != nullptr;
+ }
+
+ /* Explicit cast operators to allow things like (char16_t*)str. */
+ explicit operator char16_t*() const
+ {
+ return const_cast<char16_t*>(mPtr);
+ }
+ explicit operator wchar_t*() const
+ {
+ return const_cast<wchar_t*>(static_cast<const wchar_t*>(*this));
+ }
+ explicit operator int() const
+ {
+ return reinterpret_cast<intptr_t>(mPtr);
+ }
+ explicit operator unsigned int() const
+ {
+ return reinterpret_cast<uintptr_t>(mPtr);
+ }
+ explicit operator long() const
+ {
+ return reinterpret_cast<intptr_t>(mPtr);
+ }
+ explicit operator unsigned long() const
+ {
+ return reinterpret_cast<uintptr_t>(mPtr);
+ }
+ explicit operator long long() const
+ {
+ return reinterpret_cast<intptr_t>(mPtr);
+ }
+ explicit operator unsigned long long() const
+ {
+ return reinterpret_cast<uintptr_t>(mPtr);
+ }
+
+ /**
+ * Some Windows API calls accept BYTE* but require that data actually be
+ * WCHAR*. Supporting this requires explicit operators to support the
+ * requisite explicit casts.
+ */
+ explicit operator const char*() const
+ {
+ return reinterpret_cast<const char*>(mPtr);
+ }
+ explicit operator const unsigned char*() const
+ {
+ return reinterpret_cast<const unsigned char*>(mPtr);
+ }
+ explicit operator unsigned char*() const
+ {
+ return
+ const_cast<unsigned char*>(reinterpret_cast<const unsigned char*>(mPtr));
+ }
+ explicit operator void*() const
+ {
+ return const_cast<char16_t*>(mPtr);
+ }
+
+ /* Some operators used on pointers. */
+ char16_t operator[](size_t aIndex) const
+ {
+ return mPtr[aIndex];
+ }
+ bool operator==(const char16ptr_t& aOther) const
+ {
+ return mPtr == aOther.mPtr;
+ }
+ bool operator==(decltype(nullptr)) const
+ {
+ return mPtr == nullptr;
+ }
+ bool operator!=(const char16ptr_t& aOther) const
+ {
+ return mPtr != aOther.mPtr;
+ }
+ bool operator!=(decltype(nullptr)) const
+ {
+ return mPtr != nullptr;
+ }
+ char16ptr_t operator+(int aValue) const
+ {
+ return char16ptr_t(mPtr + aValue);
+ }
+ char16ptr_t operator+(unsigned int aValue) const
+ {
+ return char16ptr_t(mPtr + aValue);
+ }
+ char16ptr_t operator+(long aValue) const
+ {
+ return char16ptr_t(mPtr + aValue);
+ }
+ char16ptr_t operator+(unsigned long aValue) const
+ {
+ return char16ptr_t(mPtr + aValue);
+ }
+ char16ptr_t operator+(long long aValue) const
+ {
+ return char16ptr_t(mPtr + aValue);
+ }
+ char16ptr_t operator+(unsigned long long aValue) const
+ {
+ return char16ptr_t(mPtr + aValue);
+ }
+ ptrdiff_t operator-(const char16ptr_t& aOther) const
+ {
+ return mPtr - aOther.mPtr;
+ }
+};
+
+inline decltype((char*)0-(char*)0)
+operator-(const char16_t* aX, const char16ptr_t aY)
+{
+ return aX - static_cast<const char16_t*>(aY);
+}
+
+#else
+
+typedef const char16_t* char16ptr_t;
+
+#endif
+
+static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
+static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
+static_assert(sizeof(u'A') == 2, "Is unicode char literal 16 bits?");
+static_assert(sizeof(u""[0]) == 2, "Is unicode string char 16 bits?");
+
+#endif
+
+#endif /* mozilla_Char16_h */