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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 // TODO: __builtin_ctzg is available since Clang 19 and GCC 14. When support for older versions is dropped, we can 10 // refactor this code to exclusively use __builtin_ctzg. 11 12 #ifndef _LIBCPP___CXX03___BIT_COUNTR_H 13 #define _LIBCPP___CXX03___BIT_COUNTR_H 14 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_header 21 #endif 22 23 _LIBCPP_PUSH_MACROS 24 #include <__cxx03/__undef_macros> 25 26 _LIBCPP_BEGIN_NAMESPACE_STD 27 __libcpp_ctz(unsigned __x)28_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI int __libcpp_ctz(unsigned __x) _NOEXCEPT { return __builtin_ctz(__x); } 29 __libcpp_ctz(unsigned long __x)30_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI int __libcpp_ctz(unsigned long __x) _NOEXCEPT { 31 return __builtin_ctzl(__x); 32 } 33 __libcpp_ctz(unsigned long long __x)34_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI int __libcpp_ctz(unsigned long long __x) _NOEXCEPT { 35 return __builtin_ctzll(__x); 36 } 37 38 template <class _Tp> __countr_zero(_Tp __t)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_STD 64 65 _LIBCPP_POP_MACROS 66 67 #endif // _LIBCPP___CXX03___BIT_COUNTR_H 68