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 /*
  13  * C11 and C++11 introduce a char16_t type and support for UTF-16 string and
  14  * character literals. C++11's char16_t is a distinct builtin type. C11's
  15  * char16_t is a typedef for uint_least16_t. Technically, char16_t is a 16-bit
  16  * code unit of a Unicode code point, not a "character".
  17  */
  18
  19 #ifdef _MSC_VER
  20    /*
  21     * C++11 says char16_t is a distinct builtin type, but Windows's yvals.h
  22     * typedefs char16_t as an unsigned short. We would like to alias char16_t
  23     * to Windows's 16-bit wchar_t so we can declare UTF-16 literals as constant
  24     * expressions (and pass char16_t pointers to Windows APIs). We #define
  25     * _CHAR16T here in order to prevent yvals.h from overriding our char16_t
  26     * typedefs, which we set to wchar_t for C++ code and to unsigned short for
  27     * 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 #  ifdef __cplusplus
  36      typedef wchar_t char16_t;
  37 #  else
  38      typedef unsigned short char16_t;
  39 #  endif
  40    typedef unsigned int char32_t;
  41 #elif defined(__cplusplus) && \
  42       (__cplusplus >= 201103L || defined(__GXX_EXPERIMENTAL_CXX0X__))
  43    /* C++11 has a builtin char16_t type. */
  44 #  define MOZ_UTF16_HELPER(s) u##s
  45    /**
  46     * This macro is used to distinguish when char16_t would be a distinct
  47     * typedef from wchar_t.
  48     */
  49 #  define MOZ_CHAR16_IS_NOT_WCHAR
  50 #elif !defined(__cplusplus)
  51 #  if defined(WIN32)
  52 #    include <yvals.h>
  53      typedef wchar_t char16_t;
  54 #  else
  55      /**
  56       * We can't use the stdint.h uint16_t type here because including
  57       * stdint.h will break building some of our C libraries, such as
  58       * sqlite.
  59       */
  60      typedef unsigned short char16_t;
  61 #  endif
  62 #else
  63 #  error "Char16.h requires C++11 (or something like it) for UTF-16 support."
  64 #endif
  65
  66 /* This is a temporary hack until bug 927728 is fixed. */
  67 #define __PRUNICHAR__
  68 typedef char16_t PRUnichar;
  69
  70 /*
  71  * Macro arguments used in concatenation or stringification won't be expanded.
  72  * Therefore, in order for |MOZ_UTF16(FOO)| to work as expected (which is to
  73  * expand |FOO| before doing whatever |MOZ_UTF16| needs to do to it) a helper
  74  * macro, |MOZ_UTF16_HELPER| needs to be inserted in between to allow the macro
  75  * argument to expand. See "3.10.6 Separate Expansion of Macro Arguments" of the
  76  * CPP manual for a more accurate and precise explanation.
  77  */
  78 #define MOZ_UTF16(s) MOZ_UTF16_HELPER(s)
  79
  80 #if defined(__cplusplus) && \
  81     (__cplusplus >= 201103L || defined(__GXX_EXPERIMENTAL_CXX0X__))
  82 static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
  83 static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
  84 static_assert(sizeof(MOZ_UTF16('A')) == 2, "Is char literal 16 bits?");
  85 static_assert(sizeof(MOZ_UTF16("")[0]) == 2, "Is string char 16 bits?");
  86 #endif
  87
  88 #endif /* mozilla_Char16_h */