mfbt/Char16.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* Implements a UTF-16 character type. */
   8
   9 #ifndef mozilla_Char16_h
  10 #define mozilla_Char16_h
  11
  12 #ifdef __cplusplus
  13
  14 /*
  15  * C++11 introduces a char16_t type and support for UTF-16 string and character
  16  * literals. C++11's char16_t is a distinct builtin type. Technically, char16_t
  17  * is a 16-bit code unit of a Unicode code point, not a "character".
  18  */
  19
  20 #ifdef _MSC_VER
  21    /*
  22     * C++11 says char16_t is a distinct builtin type, but Windows's yvals.h
  23     * typedefs char16_t as an unsigned short. We would like to alias char16_t
  24     * to Windows's 16-bit wchar_t so we can declare UTF-16 literals as constant
  25     * expressions (and pass char16_t pointers to Windows APIs). We #define
  26     * _CHAR16T here in order to prevent yvals.h from overriding our char16_t
  27     * typedefs, which we set to wchar_t for C++ code.
  28     *
  29     * In addition, #defining _CHAR16T will prevent yvals.h from defining a
  30     * char32_t type, so we have to undo that damage here and provide our own,
  31     * which is identical to the yvals.h type.
  32     */
  33 #  define MOZ_UTF16_HELPER(s) L##s
  34 #  define _CHAR16T
  35 typedef wchar_t char16_t;
  36 typedef unsigned int char32_t;
  37 #else
  38    /* C++11 has a builtin char16_t type. */
  39 #  define MOZ_UTF16_HELPER(s) u##s
  40    /**
  41     * This macro is used to distinguish when char16_t would be a distinct
  42     * typedef from wchar_t.
  43     */
  44 #  define MOZ_CHAR16_IS_NOT_WCHAR
  45 #  ifdef WIN32
  46 #    define MOZ_USE_CHAR16_WRAPPER
  47 #  endif
  48 #endif
  49
  50 #ifdef MOZ_USE_CHAR16_WRAPPER
  51 # include <string>
  52   /**
  53    * Win32 API extensively uses wchar_t, which is represented by a separated
  54    * builtin type than char16_t per spec. It's not the case for MSVC, but GCC
  55    * follows the spec. We want to mix wchar_t and char16_t on Windows builds.
  56    * This class is supposed to make it easier. It stores char16_t const pointer,
  57    * but provides implicit casts for wchar_t as well. On other platforms, we
  58    * simply use |typedef const char16_t* char16ptr_t|. Here, we want to make
  59    * the class as similar to this typedef, including providing some casts that
  60    * are allowed by the typedef.
  61    */
  62 class char16ptr_t
  63 {
  64 private:
  65   const char16_t* mPtr;
  66   static_assert(sizeof(char16_t) == sizeof(wchar_t),
  67                 "char16_t and wchar_t sizes differ");
  68
  69 public:
  70   char16ptr_t(const char16_t* aPtr) : mPtr(aPtr) {}
  71   char16ptr_t(const wchar_t* aPtr) :
  72     mPtr(reinterpret_cast<const char16_t*>(aPtr))
  73   {}
  74
  75   /* Without this, nullptr assignment would be ambiguous. */
  76   constexpr char16ptr_t(decltype(nullptr)) : mPtr(nullptr) {}
  77
  78   operator const char16_t*() const
  79   {
  80     return mPtr;
  81   }
  82   operator const wchar_t*() const
  83   {
  84     return reinterpret_cast<const wchar_t*>(mPtr);
  85   }
  86   operator const void*() const
  87   {
  88     return mPtr;
  89   }
  90   operator bool() const
  91   {
  92     return mPtr != nullptr;
  93   }
  94   operator std::wstring() const
  95   {
  96     return std::wstring(static_cast<const wchar_t*>(*this));
  97   }
  98
  99   /* Explicit cast operators to allow things like (char16_t*)str. */
 100   explicit operator char16_t*() const
 101   {
 102     return const_cast<char16_t*>(mPtr);
 103   }
 104   explicit operator wchar_t*() const
 105   {
 106     return const_cast<wchar_t*>(static_cast<const wchar_t*>(*this));
 107   }
 108
 109   /**
 110    * Some Windows API calls accept BYTE* but require that data actually be WCHAR*.
 111    * Supporting this requires explicit operators to support the requisite explicit
 112    * casts.
 113    */
 114   explicit operator const char*() const
 115   {
 116     return reinterpret_cast<const char*>(mPtr);
 117   }
 118   explicit operator const unsigned char*() const
 119   {
 120     return reinterpret_cast<const unsigned char*>(mPtr);
 121   }
 122   explicit operator unsigned char*() const
 123   {
 124     return const_cast<unsigned char*>(reinterpret_cast<const unsigned char*>(mPtr));
 125   }
 126   explicit operator void*() const
 127   {
 128     return const_cast<char16_t*>(mPtr);
 129   }
 130
 131   /* Some operators used on pointers. */
 132   char16_t operator[](size_t aIndex) const
 133   {
 134     return mPtr[aIndex];
 135   }
 136   bool operator==(const char16ptr_t &aOther) const
 137   {
 138     return mPtr == aOther.mPtr;
 139   }
 140   bool operator==(decltype(nullptr)) const
 141   {
 142     return mPtr == nullptr;
 143   }
 144   bool operator!=(const char16ptr_t &aOther) const
 145   {
 146     return mPtr != aOther.mPtr;
 147   }
 148   bool operator!=(decltype(nullptr)) const
 149   {
 150     return mPtr != nullptr;
 151   }
 152   char16ptr_t operator+(size_t aValue) const
 153   {
 154     return char16ptr_t(mPtr + aValue);
 155   }
 156   ptrdiff_t operator-(const char16ptr_t &aOther) const
 157   {
 158     return mPtr - aOther.mPtr;
 159   }
 160 };
 161
 162 inline decltype((char*)0-(char*)0)
 163 operator-(const char16_t* aX, const char16ptr_t aY)
 164 {
 165   return aX - static_cast<const char16_t*>(aY);
 166 }
 167
 168 #else
 169
 170 typedef const char16_t* char16ptr_t;
 171
 172 #endif
 173
 174 /*
 175  * Macro arguments used in concatenation or stringification won't be expanded.
 176  * Therefore, in order for |MOZ_UTF16(FOO)| to work as expected (which is to
 177  * expand |FOO| before doing whatever |MOZ_UTF16| needs to do to it) a helper
 178  * macro, |MOZ_UTF16_HELPER| needs to be inserted in between to allow the macro
 179  * argument to expand. See "3.10.6 Separate Expansion of Macro Arguments" of the
 180  * CPP manual for a more accurate and precise explanation.
 181  */
 182 #define MOZ_UTF16(s) MOZ_UTF16_HELPER(s)
 183
 184 static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
 185 static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
 186 static_assert(sizeof(MOZ_UTF16('A')) == 2, "Is char literal 16 bits?");
 187 static_assert(sizeof(MOZ_UTF16("")[0]) == 2, "Is string char 16 bits?");
 188
 189 #endif
 190
 191 #endif /* mozilla_Char16_h */