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 WIN32
  21 # define MOZ_USE_CHAR16_WRAPPER
  22 # include <cstdint>
  23 # include "mozilla/Attributes.h"
  24   /**
  25    * Win32 API extensively uses wchar_t, which is represented by a separated
  26    * builtin type than char16_t per spec. It's not the case for MSVC prior to
  27    * MSVC 2015, but other compilers follow the spec. We want to mix wchar_t and
  28    * char16_t on Windows builds. This class is supposed to make it easier. It
  29    * stores char16_t const pointer, but provides implicit casts for wchar_t as
  30    * well. On other platforms, we simply use
  31    * |typedef const char16_t* char16ptr_t|. Here, we want to make the class as
  32    * similar to this typedef, including providing some casts that are allowed
  33    * by the typedef.
  34    */
  35 class char16ptr_t
  36 {
  37 private:
  38   const char16_t* mPtr;
  39   static_assert(sizeof(char16_t) == sizeof(wchar_t),
  40                 "char16_t and wchar_t sizes differ");
  41
  42 public:
  43   MOZ_IMPLICIT char16ptr_t(const char16_t* aPtr) : mPtr(aPtr) {}
  44   MOZ_IMPLICIT char16ptr_t(const wchar_t* aPtr) :
  45     mPtr(reinterpret_cast<const char16_t*>(aPtr))
  46   {}
  47
  48   /* Without this, nullptr assignment would be ambiguous. */
  49   constexpr MOZ_IMPLICIT char16ptr_t(decltype(nullptr)) : mPtr(nullptr) {}
  50
  51   operator const char16_t*() const
  52   {
  53     return mPtr;
  54   }
  55   operator const wchar_t*() const
  56   {
  57     return reinterpret_cast<const wchar_t*>(mPtr);
  58   }
  59
  60   operator wchar_t*()
  61   {
  62     return const_cast<wchar_t*>(reinterpret_cast<const wchar_t*>(mPtr));
  63   }
  64
  65   operator const void*() const
  66   {
  67     return mPtr;
  68   }
  69   explicit operator bool() const
  70   {
  71     return mPtr != nullptr;
  72   }
  73
  74   /* Explicit cast operators to allow things like (char16_t*)str. */
  75   explicit operator char16_t*() const
  76   {
  77     return const_cast<char16_t*>(mPtr);
  78   }
  79   explicit operator wchar_t*() const
  80   {
  81     return const_cast<wchar_t*>(static_cast<const wchar_t*>(*this));
  82   }
  83   explicit operator int() const
  84   {
  85     return reinterpret_cast<intptr_t>(mPtr);
  86   }
  87   explicit operator unsigned int() const
  88   {
  89     return reinterpret_cast<uintptr_t>(mPtr);
  90   }
  91   explicit operator long() const
  92   {
  93     return reinterpret_cast<intptr_t>(mPtr);
  94   }
  95   explicit operator unsigned long() const
  96   {
  97     return reinterpret_cast<uintptr_t>(mPtr);
  98   }
  99   explicit operator long long() const
 100   {
 101     return reinterpret_cast<intptr_t>(mPtr);
 102   }
 103   explicit operator unsigned long long() const
 104   {
 105     return reinterpret_cast<uintptr_t>(mPtr);
 106   }
 107
 108   /**
 109    * Some Windows API calls accept BYTE* but require that data actually be
 110    * WCHAR*.  Supporting this requires explicit operators to support the
 111    * requisite explicit casts.
 112    */
 113   explicit operator const char*() const
 114   {
 115     return reinterpret_cast<const char*>(mPtr);
 116   }
 117   explicit operator const unsigned char*() const
 118   {
 119     return reinterpret_cast<const unsigned char*>(mPtr);
 120   }
 121   explicit operator unsigned char*() const
 122   {
 123     return
 124       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+(int aValue) const
 153   {
 154     return char16ptr_t(mPtr + aValue);
 155   }
 156   char16ptr_t operator+(unsigned int aValue) const
 157   {
 158     return char16ptr_t(mPtr + aValue);
 159   }
 160   char16ptr_t operator+(long aValue) const
 161   {
 162     return char16ptr_t(mPtr + aValue);
 163   }
 164   char16ptr_t operator+(unsigned long aValue) const
 165   {
 166     return char16ptr_t(mPtr + aValue);
 167   }
 168   char16ptr_t operator+(long long aValue) const
 169   {
 170     return char16ptr_t(mPtr + aValue);
 171   }
 172   char16ptr_t operator+(unsigned long long aValue) const
 173   {
 174     return char16ptr_t(mPtr + aValue);
 175   }
 176   ptrdiff_t operator-(const char16ptr_t& aOther) const
 177   {
 178     return mPtr - aOther.mPtr;
 179   }
 180 };
 181
 182 inline decltype((char*)0-(char*)0)
 183 operator-(const char16_t* aX, const char16ptr_t aY)
 184 {
 185   return aX - static_cast<const char16_t*>(aY);
 186 }
 187
 188 #else
 189
 190 typedef const char16_t* char16ptr_t;
 191
 192 #endif
 193
 194 static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
 195 static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
 196 static_assert(sizeof(u'A') == 2, "Is unicode char literal 16 bits?");
 197 static_assert(sizeof(u""[0]) == 2, "Is unicode string char 16 bits?");
 198
 199 #endif
 200
 201 #endif /* mozilla_Char16_h */