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  private:
  37   const char16_t* mPtr;
  38   static_assert(sizeof(char16_t) == sizeof(wchar_t),
  39                 "char16_t and wchar_t sizes differ");
  40
  41  public:
  42   constexpr MOZ_IMPLICIT char16ptr_t(const char16_t* aPtr) : mPtr(aPtr) {}
  43   MOZ_IMPLICIT char16ptr_t(const wchar_t* aPtr)
  44       : mPtr(reinterpret_cast<const char16_t*>(aPtr)) {}
  45
  46   /* Without this, nullptr assignment would be ambiguous. */
  47   constexpr MOZ_IMPLICIT char16ptr_t(decltype(nullptr)) : mPtr(nullptr) {}
  48
  49   constexpr operator const char16_t*() const { return mPtr; }
  50   operator const wchar_t*() const {
  51     return reinterpret_cast<const wchar_t*>(mPtr);
  52   }
  53
  54   operator wchar_t*() {
  55     return const_cast<wchar_t*>(reinterpret_cast<const wchar_t*>(mPtr));
  56   }
  57
  58   constexpr operator const void*() const { return mPtr; }
  59   constexpr explicit operator bool() const { return mPtr != nullptr; }
  60
  61   /* Explicit cast operators to allow things like (char16_t*)str. */
  62   constexpr explicit operator char16_t*() const {
  63     return const_cast<char16_t*>(mPtr);
  64   }
  65   explicit operator wchar_t*() const {
  66     return const_cast<wchar_t*>(static_cast<const wchar_t*>(*this));
  67   }
  68   explicit operator int() const { return reinterpret_cast<intptr_t>(mPtr); }
  69   explicit operator unsigned int() const {
  70     return reinterpret_cast<uintptr_t>(mPtr);
  71   }
  72   explicit operator long() const { return reinterpret_cast<intptr_t>(mPtr); }
  73   explicit operator unsigned long() const {
  74     return reinterpret_cast<uintptr_t>(mPtr);
  75   }
  76   explicit operator long long() const {
  77     return reinterpret_cast<intptr_t>(mPtr);
  78   }
  79   explicit operator unsigned long long() const {
  80     return reinterpret_cast<uintptr_t>(mPtr);
  81   }
  82
  83   /**
  84    * Some Windows API calls accept BYTE* but require that data actually be
  85    * WCHAR*.  Supporting this requires explicit operators to support the
  86    * requisite explicit casts.
  87    */
  88   explicit operator const char*() const {
  89     return reinterpret_cast<const char*>(mPtr);
  90   }
  91   explicit operator const unsigned char*() const {
  92     return reinterpret_cast<const unsigned char*>(mPtr);
  93   }
  94   explicit operator unsigned char*() const {
  95     return const_cast<unsigned char*>(
  96         reinterpret_cast<const unsigned char*>(mPtr));
  97   }
  98   explicit operator void*() const { return const_cast<char16_t*>(mPtr); }
  99
 100   /* Some operators used on pointers. */
 101   char16_t operator[](size_t aIndex) const { return mPtr[aIndex]; }
 102   bool operator==(const char16ptr_t& aOther) const {
 103     return mPtr == aOther.mPtr;
 104   }
 105   bool operator==(decltype(nullptr)) const { return mPtr == nullptr; }
 106   bool operator!=(const char16ptr_t& aOther) const {
 107     return mPtr != aOther.mPtr;
 108   }
 109   bool operator!=(decltype(nullptr)) const { return mPtr != nullptr; }
 110   char16ptr_t operator+(int aValue) const { return char16ptr_t(mPtr + aValue); }
 111   char16ptr_t operator+(unsigned int aValue) const {
 112     return char16ptr_t(mPtr + aValue);
 113   }
 114   char16ptr_t operator+(long aValue) const {
 115     return char16ptr_t(mPtr + aValue);
 116   }
 117   char16ptr_t operator+(unsigned long aValue) const {
 118     return char16ptr_t(mPtr + aValue);
 119   }
 120   char16ptr_t operator+(long long aValue) const {
 121     return char16ptr_t(mPtr + aValue);
 122   }
 123   char16ptr_t operator+(unsigned long long aValue) const {
 124     return char16ptr_t(mPtr + aValue);
 125   }
 126   ptrdiff_t operator-(const char16ptr_t& aOther) const {
 127     return mPtr - aOther.mPtr;
 128   }
 129 };
 130
 131 inline decltype((char*)0 - (char*)0) operator-(const char16_t* aX,
 132                                                const char16ptr_t aY) {
 133   return aX - static_cast<const char16_t*>(aY);
 134 }
 135
 136 #  else
 137
 138 typedef const char16_t* char16ptr_t;
 139
 140 #  endif
 141
 142 static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
 143 static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
 144 static_assert(sizeof(u'A') == 2, "Is unicode char literal 16 bits?");
 145 static_assert(sizeof(u""[0]) == 2, "Is unicode string char 16 bits?");
 146
 147 #endif
 148
 149 #endif /* mozilla_Char16_h */