ba87515fea
Currently, the library-internal feature test macros are only defined if the feature is not available, and always have the prefix `_LIBCPP_HAS_NO_`. This patch changes that, so that they are always defined and have the prefix `_LIBCPP_HAS_` instead. This changes the canonical use of these macros to `#if _LIBCPP_HAS_FEATURE`, which means that using an undefined macro (e.g. due to a missing include) is diagnosed now. While this is rather unlikely currently, a similar change in `<__configuration/availability.h>` caught a few bugs. This also improves readability, since it removes the double-negation of `#ifndef _LIBCPP_HAS_NO_FEATURE`. The current patch only touches the macros defined in `<__config>`. If people are happy with this approach, I'll make a follow-up PR to also change the macros defined in `<__config_site>`.
67 lines
1.9 KiB
C++
67 lines
1.9 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___RANDOM_LOG2_H
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#define _LIBCPP___RANDOM_LOG2_H
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#include <__config>
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#include <__type_traits/conditional.h>
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#include <cstddef>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class _UIntType, _UIntType _Xp, size_t _Rp>
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struct __log2_imp;
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template <unsigned long long _Xp, size_t _Rp>
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struct __log2_imp<unsigned long long, _Xp, _Rp> {
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static const size_t value =
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_Xp & ((unsigned long long)(1) << _Rp) ? _Rp : __log2_imp<unsigned long long, _Xp, _Rp - 1>::value;
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};
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template <unsigned long long _Xp>
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struct __log2_imp<unsigned long long, _Xp, 0> {
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static const size_t value = 0;
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};
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template <size_t _Rp>
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struct __log2_imp<unsigned long long, 0, _Rp> {
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static const size_t value = _Rp + 1;
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};
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#if _LIBCPP_HAS_INT128
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template <__uint128_t _Xp, size_t _Rp>
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struct __log2_imp<__uint128_t, _Xp, _Rp> {
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static const size_t value =
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(_Xp >> 64) ? (64 + __log2_imp<unsigned long long, (_Xp >> 64), 63>::value)
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: __log2_imp<unsigned long long, _Xp, 63>::value;
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};
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#endif // _LIBCPP_HAS_INT128
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template <class _UIntType, _UIntType _Xp>
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struct __log2 {
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static const size_t value = __log2_imp<
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#if _LIBCPP_HAS_INT128
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__conditional_t<sizeof(_UIntType) <= sizeof(unsigned long long), unsigned long long, __uint128_t>,
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#else
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unsigned long long,
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#endif // _LIBCPP_HAS_INT128
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_Xp,
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sizeof(_UIntType) * __CHAR_BIT__ - 1>::value;
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};
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___RANDOM_LOG2_H
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