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113 lines
4.1 KiB
C++
113 lines
4.1 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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// TODO: __builtin_clzg is available since Clang 19 and GCC 14. When support for older versions is dropped, we can
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// refactor this code to exclusively use __builtin_clzg.
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#ifndef _LIBCPP___BIT_COUNTL_H
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#define _LIBCPP___BIT_COUNTL_H
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#include <__bit/rotate.h>
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#include <__concepts/arithmetic.h>
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#include <__config>
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#include <__type_traits/is_unsigned_integer.h>
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#include <limits>
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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_PUSH_MACROS
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#include <__undef_macros>
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_LIBCPP_BEGIN_NAMESPACE_STD
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_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned __x) _NOEXCEPT {
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return __builtin_clz(__x);
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}
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_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long __x) _NOEXCEPT {
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return __builtin_clzl(__x);
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}
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_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long long __x) _NOEXCEPT {
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return __builtin_clzll(__x);
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}
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#ifndef _LIBCPP_HAS_NO_INT128
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inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(__uint128_t __x) _NOEXCEPT {
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# if __has_builtin(__builtin_clzg)
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return __builtin_clzg(__x);
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# else
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// The function is written in this form due to C++ constexpr limitations.
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// The algorithm:
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// - Test whether any bit in the high 64-bits is set
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// - No bits set:
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// - The high 64-bits contain 64 leading zeros,
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// - Add the result of the low 64-bits.
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// - Any bits set:
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// - The number of leading zeros of the input is the number of leading
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// zeros in the high 64-bits.
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return ((__x >> 64) == 0) ? (64 + __builtin_clzll(static_cast<unsigned long long>(__x)))
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: __builtin_clzll(static_cast<unsigned long long>(__x >> 64));
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# endif
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}
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#endif // _LIBCPP_HAS_NO_INT128
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template <class _Tp>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countl_zero(_Tp __t) _NOEXCEPT {
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static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__countl_zero requires an unsigned integer type");
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#if __has_builtin(__builtin_clzg)
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return __builtin_clzg(__t, numeric_limits<_Tp>::digits);
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#else // __has_builtin(__builtin_clzg)
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if (__t == 0)
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return numeric_limits<_Tp>::digits;
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if (sizeof(_Tp) <= sizeof(unsigned int))
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return std::__libcpp_clz(static_cast<unsigned int>(__t)) -
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(numeric_limits<unsigned int>::digits - numeric_limits<_Tp>::digits);
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else if (sizeof(_Tp) <= sizeof(unsigned long))
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return std::__libcpp_clz(static_cast<unsigned long>(__t)) -
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(numeric_limits<unsigned long>::digits - numeric_limits<_Tp>::digits);
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else if (sizeof(_Tp) <= sizeof(unsigned long long))
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return std::__libcpp_clz(static_cast<unsigned long long>(__t)) -
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(numeric_limits<unsigned long long>::digits - numeric_limits<_Tp>::digits);
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else {
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int __ret = 0;
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int __iter = 0;
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const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
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while (true) {
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__t = std::__rotl(__t, __ulldigits);
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if ((__iter = std::__countl_zero(static_cast<unsigned long long>(__t))) != __ulldigits)
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break;
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__ret += __iter;
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}
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return __ret + __iter;
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}
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#endif // __has_builtin(__builtin_clzg)
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}
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#if _LIBCPP_STD_VER >= 20
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template <__libcpp_unsigned_integer _Tp>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
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return std::__countl_zero(__t);
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}
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template <__libcpp_unsigned_integer _Tp>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countl_one(_Tp __t) noexcept {
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return __t != numeric_limits<_Tp>::max() ? std::countl_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
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}
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#endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_END_NAMESPACE_STD
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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___BIT_COUNTL_H
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