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64 lines
2.6 KiB
C
64 lines
2.6 KiB
C
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* Implements a UTF-16 character type. */
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#ifndef mozilla_Char16_h
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#define mozilla_Char16_h
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#include "mozilla/Assertions.h"
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/*
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* C11 and C++11 introduce a char16_t type and support for UTF-16 string and
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* character literals. C++11's char16_t is a distinct builtin type. C11's
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* char16_t is a typedef for uint_least16_t. Technically, char16_t is a 16-bit
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* code unit of a Unicode code point, not a "character".
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*
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* For now, Char16.h only supports C++ because we don't want mix different C
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* and C++ definitions of char16_t in the same code base.
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*/
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#ifdef _MSC_VER
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/*
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* C++11 says char16_t is a distinct builtin type, but Windows's yvals.h
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* typedefs char16_t as an unsigned short. We would like to alias char16_t
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* to Windows's 16-bit wchar_t so we can declare UTF-16 literals as constant
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* expressions (and pass char16_t pointers to Windows APIs). We #define our
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* char16_t as a macro to override yval.h's typedef of the same name.
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*/
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# define MOZ_UTF16_HELPER(s) L##s
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# include <yvals.h>
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# define char16_t wchar_t
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#elif defined(__cplusplus) && \
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(__cplusplus >= 201103L || defined(__GXX_EXPERIMENTAL_CXX0X__))
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/* C++11 has a builtin char16_t type. */
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# define MOZ_UTF16_HELPER(s) u##s
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/**
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* This macro is used to distinguish when char16_t would be a distinct
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* typedef from wchar_t.
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*/
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# define MOZ_CHAR16_IS_NOT_WCHAR
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#else
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# error "Char16.h requires C++11 (or something like it) for UTF-16 support."
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#endif
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/*
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* Macro arguments used in concatenation or stringification won't be expanded.
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* Therefore, in order for |MOZ_UTF16(FOO)| to work as expected (which is to
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* expand |FOO| before doing whatever |MOZ_UTF16| needs to do to it) a helper
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* macro, |MOZ_UTF16_HELPER| needs to be inserted in between to allow the macro
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* argument to expand. See "3.10.6 Separate Expansion of Macro Arguments" of the
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* CPP manual for a more accurate and precise explanation.
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*/
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#define MOZ_UTF16(s) MOZ_UTF16_HELPER(s)
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static_assert(sizeof(char16_t) == 2, "Is char16_t type 16 bits?");
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static_assert(char16_t(-1) > char16_t(0), "Is char16_t type unsigned?");
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static_assert(sizeof(MOZ_UTF16('A')) == 2, "Is char literal 16 bits?");
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static_assert(sizeof(MOZ_UTF16("")[0]) == 2, "Is string char 16 bits?");
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#endif /* mozilla_Char16_h */
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