368faacac7
This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9, which were related to the original commit). As landed, 5aaefa51 had unintended consequences on some downstream bots and didn't have proper coverage upstream due to a few subtle things. Implementing this is something we should do in libc++, however we'll first need to address a few issues listed in https://reviews.llvm.org/D106124#3349710. Differential Revision: https://reviews.llvm.org/D120683
75 lines
2.0 KiB
C++
75 lines
2.0 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 <cstddef>
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#include <type_traits>
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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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{
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static const size_t value = _Xp & ((unsigned long long)(1) << _Rp) ? _Rp
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: __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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{
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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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{
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static const size_t value = _Rp + 1;
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};
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#ifndef _LIBCPP_HAS_NO_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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{
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static const size_t value = (_Xp >> 64)
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? (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_NO_INT128
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template <class _UIntType, _UIntType _Xp>
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struct __log2
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{
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static const size_t value = __log2_imp<
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#ifndef _LIBCPP_HAS_NO_INT128
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typename conditional<
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sizeof(_UIntType) <= sizeof(unsigned long long),
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unsigned long long,
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__uint128_t
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>::type,
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#else
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unsigned long long,
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#endif // _LIBCPP_HAS_NO_INT128
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_Xp, 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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