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   explicit operator int() const
 109   {
 110     return reinterpret_cast<intptr_t>(mPtr);
 111   }
 112   explicit operator unsigned int() const
 113   {
 114     return reinterpret_cast<uintptr_t>(mPtr);
 115   }
 116   explicit operator long() const
 117   {
 118     return reinterpret_cast<intptr_t>(mPtr);
 119   }
 120   explicit operator unsigned long() const
 121   {
 122     return reinterpret_cast<uintptr_t>(mPtr);
 123   }
 124   explicit operator long long() const
 125   {
 126     return reinterpret_cast<intptr_t>(mPtr);
 127   }
 128   explicit operator unsigned long long() const
 129   {
 130     return reinterpret_cast<uintptr_t>(mPtr);
 131   }
 132
 133   /**
 134    * Some Windows API calls accept BYTE* but require that data actually be
 135    * WCHAR*.  Supporting this requires explicit operators to support the
 136    * requisite explicit casts.
 137    */
 138   explicit operator const char*() const
 139   {
 140     return reinterpret_cast<const char*>(mPtr);
 141   }
 142   explicit operator const unsigned char*() const
 143   {
 144     return reinterpret_cast<const unsigned char*>(mPtr);
 145   }
 146   explicit operator unsigned char*() const
 147   {
 148     return
 149       const_cast<unsigned char*>(reinterpret_cast<const unsigned char*>(mPtr));
 150   }
 151   explicit operator void*() const
 152   {
 153     return const_cast<char16_t*>(mPtr);
 154   }
 155
 156   /* Some operators used on pointers. */
 157   char16_t operator[](size_t aIndex) const
 158   {
 159     return mPtr[aIndex];
 160   }
 161   bool operator==(const char16ptr_t& aOther) const
 162   {
 163     return mPtr == aOther.mPtr;
 164   }
 165   bool operator==(decltype(nullptr)) const
 166   {
 167     return mPtr == nullptr;
 168   }
 169   bool operator!=(const char16ptr_t& aOther) const
 170   {
 171     return mPtr != aOther.mPtr;
 172   }
 173   bool operator!=(decltype(nullptr)) const
 174   {
 175     return mPtr != nullptr;
 176   }
 177   char16ptr_t operator+(int aValue) const
 178   {
 179     return char16ptr_t(mPtr + aValue);
 180   }
 181   char16ptr_t operator+(unsigned int aValue) const
 182   {
 183     return char16ptr_t(mPtr + aValue);
 184   }
 185   char16ptr_t operator+(long aValue) const
 186   {
 187     return char16ptr_t(mPtr + aValue);
 188   }
 189   char16ptr_t operator+(unsigned long aValue) const
 190   {
 191     return char16ptr_t(mPtr + aValue);
 192   }
 193   char16ptr_t operator+(long long aValue) const
 194   {
 195     return char16ptr_t(mPtr + aValue);
 196   }
 197   char16ptr_t operator+(unsigned long long aValue) const
 198   {
 199     return char16ptr_t(mPtr + aValue);
 200   }
 201   ptrdiff_t operator-(const char16ptr_t& aOther) const
 202   {
 203     return mPtr - aOther.mPtr;
 204   }
 205 };
 206
 207 inline decltype((char*)0-(char*)0)
 208 operator-(const char16_t* aX, const char16ptr_t aY)
 209 {
 210   return aX - static_cast<const char16_t*>(aY);
 211 }
 212
 213 #else
 214
 215 typedef const char16_t* char16ptr_t;
 216
 217 #endif
 218
 219 /*
 220  * Macro arguments used in concatenation or stringification won't be expanded.
 221  * Therefore, in order for |MOZ_UTF16(FOO)| to work as expected (which is to
 222  * expand |FOO| before doing whatever |MOZ_UTF16| needs to do to it) a helper
 223  * macro, |MOZ_UTF16_HELPER| needs to be inserted in between to allow the macro
 224  * argument to expand. See "3.10.6 Separate Expansion of Macro Arguments" of the
 225  * CPP manual for a more accurate and precise explanation.
 226  */
 227 #define MOZ_UTF16(s) MOZ_UTF16_HELPER(s)
 228
 229 static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
 230 static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
 231 static_assert(sizeof(MOZ_UTF16('A')) == 2, "Is char literal 16 bits?");
 232 static_assert(sizeof(MOZ_UTF16("")[0]) == 2, "Is string char 16 bits?");
 233
 234 #endif
 235
 236 #endif /* mozilla_Char16_h */