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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9// TODO: __builtin_ctzg is available since Clang 19 and GCC 14. When support for older versions is dropped, we can10// refactor this code to exclusively use __builtin_ctzg.11 12#ifndef _LIBCPP___CXX03___BIT_COUNTR_H13#define _LIBCPP___CXX03___BIT_COUNTR_H14 15#include <__cxx03/__bit/rotate.h>16#include <__cxx03/__config>17#include <__cxx03/limits>18 19#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)20# pragma GCC system_header21#endif22 23_LIBCPP_PUSH_MACROS24#include <__cxx03/__undef_macros>25 26_LIBCPP_BEGIN_NAMESPACE_STD27 28_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI int __libcpp_ctz(unsigned __x) _NOEXCEPT { return __builtin_ctz(__x); }29 30_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI int __libcpp_ctz(unsigned long __x) _NOEXCEPT {31 return __builtin_ctzl(__x);32}33 34_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI int __libcpp_ctz(unsigned long long __x) _NOEXCEPT {35 return __builtin_ctzll(__x);36}37 38template <class _Tp>39_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI int __countr_zero(_Tp __t) _NOEXCEPT {40#if __has_builtin(__builtin_ctzg)41 return __builtin_ctzg(__t, numeric_limits<_Tp>::digits);42#else // __has_builtin(__builtin_ctzg)43 if (__t == 0)44 return numeric_limits<_Tp>::digits;45 if (sizeof(_Tp) <= sizeof(unsigned int))46 return std::__libcpp_ctz(static_cast<unsigned int>(__t));47 else if (sizeof(_Tp) <= sizeof(unsigned long))48 return std::__libcpp_ctz(static_cast<unsigned long>(__t));49 else if (sizeof(_Tp) <= sizeof(unsigned long long))50 return std::__libcpp_ctz(static_cast<unsigned long long>(__t));51 else {52 int __ret = 0;53 const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;54 while (static_cast<unsigned long long>(__t) == 0uLL) {55 __ret += __ulldigits;56 __t >>= __ulldigits;57 }58 return __ret + std::__libcpp_ctz(static_cast<unsigned long long>(__t));59 }60#endif // __has_builtin(__builtin_ctzg)61}62 63_LIBCPP_END_NAMESPACE_STD64 65_LIBCPP_POP_MACROS66 67#endif // _LIBCPP___CXX03___BIT_COUNTR_H68