author Benoit Girard <>
Sat, 03 May 2014 20:35:47 -0400
changeset 193923 d572fe88d3eb7ae69a6f7da1f53af9678179cc42
parent 183777 7b8c2a48d08bf8642ee5cc5187b5b65e2ced1e24
child 198256 038794b1a5bc9886976d9eac1d626f7b31e027b3
permissions -rw-r--r--
Bug 1005298 - Add layout.display-list.dump Preference. r=mattwoodrow

/* -*- 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 */

/* 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 _MSC_VER
    * C++11 says char16_t is a distinct builtin type, but Windows's yvals.h
    * typedefs char16_t as an unsigned short. We would like to alias char16_t
    * to Windows's 16-bit wchar_t so we can declare UTF-16 literals as constant
    * expressions (and pass char16_t pointers to Windows APIs). We #define
    * _CHAR16T here in order to prevent yvals.h from overriding our char16_t
    * typedefs, which we set to wchar_t for C++ code.
    * In addition, #defining _CHAR16T will prevent yvals.h from defining a
    * char32_t type, so we have to undo that damage here and provide our own,
    * which is identical to the yvals.h type.
#  define MOZ_UTF16_HELPER(s) L##s
#  define _CHAR16T
   typedef wchar_t char16_t;
   typedef unsigned int char32_t;
   /* C++11 has a builtin char16_t type. */
#  define MOZ_UTF16_HELPER(s) u##s
    * This macro is used to distinguish when char16_t would be a distinct
    * typedef from wchar_t.
#  ifdef WIN32
#    define MOZ_USE_CHAR16_WRAPPER
#  endif

# include <string>
   * 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, but GCC
   * follows 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
    const char16_t* ptr;
    static_assert(sizeof(char16_t) == sizeof(wchar_t), "char16_t and wchar_t sizes differ");

    char16ptr_t(const char16_t* p) : ptr(p) {}
    char16ptr_t(const wchar_t* p) : ptr(reinterpret_cast<const char16_t*>(p)) {}

    /* Without this, nullptr assignment would be ambiguous. */
    constexpr char16ptr_t(decltype(nullptr)) : ptr(nullptr) {}

    operator const char16_t*() const {
      return ptr;
    operator const wchar_t*() const {
      return reinterpret_cast<const wchar_t*>(ptr);
    operator const void*() const {
      return ptr;
    operator bool() const {
      return ptr != nullptr;
    operator std::wstring() const {
      return std::wstring(static_cast<const wchar_t*>(*this));

    /* Explicit cast operators to allow things like (char16_t*)str. */
    explicit operator char16_t*() const {
      return const_cast<char16_t*>(ptr);
    explicit operator wchar_t*() const {
      return const_cast<wchar_t*>(static_cast<const wchar_t*>(*this));

     * 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*>(ptr);
    explicit operator const unsigned char*() const {
      return reinterpret_cast<const unsigned char*>(ptr);
    explicit operator unsigned char*() const {
      return const_cast<unsigned char*>(reinterpret_cast<const unsigned char*>(ptr));
    explicit operator void*() const {
      return const_cast<char16_t*>(ptr);

    /* Some operators used on pointers. */
    char16_t operator[](size_t i) const {
      return ptr[i];
    bool operator==(const char16ptr_t &x) const {
      return ptr == x.ptr;
    bool operator==(decltype(nullptr)) const {
      return ptr == nullptr;
    bool operator!=(const char16ptr_t &x) const {
      return ptr != x.ptr;
    bool operator!=(decltype(nullptr)) const {
      return ptr != nullptr;
    char16ptr_t operator+(size_t add) const {
      return char16ptr_t(ptr + add);
    ptrdiff_t operator-(const char16ptr_t &other) const {
      return ptr - other.ptr;

inline decltype((char*)0-(char*)0)
operator-(const char16_t* x, const char16ptr_t y) {
  return x - static_cast<const char16_t*>(y);


typedef const char16_t* char16ptr_t;


 * Macro arguments used in concatenation or stringification won't be expanded.
 * Therefore, in order for |MOZ_UTF16(FOO)| to work as expected (which is to
 * expand |FOO| before doing whatever |MOZ_UTF16| needs to do to it) a helper
 * macro, |MOZ_UTF16_HELPER| needs to be inserted in between to allow the macro
 * argument to expand. See "3.10.6 Separate Expansion of Macro Arguments" of the
 * CPP manual for a more accurate and precise explanation.
#define MOZ_UTF16(s) MOZ_UTF16_HELPER(s)

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(MOZ_UTF16('A')) == 2, "Is char literal 16 bits?");
static_assert(sizeof(MOZ_UTF16("")[0]) == 2, "Is string char 16 bits?");


#endif /* mozilla_Char16_h */