__cxx03/__bit/countr.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 // TODO: __builtin_ctzg is available since Clang 19 and GCC 14. When support for older versions is dropped, we can
0010 //  refactor this code to exclusively use __builtin_ctzg.
0011
0012 #ifndef _LIBCPP___CXX03___BIT_COUNTR_H
0013 #define _LIBCPP___CXX03___BIT_COUNTR_H
0014
0015 #include <__cxx03/__bit/rotate.h>
0016 #include <__cxx03/__concepts/arithmetic.h>
0017 #include <__cxx03/__config>
0018 #include <__cxx03/limits>
0019
0020 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0021 #  pragma GCC system_header
0022 #endif
0023
0024 _LIBCPP_PUSH_MACROS
0025 #include <__cxx03/__undef_macros>
0026
0027 _LIBCPP_BEGIN_NAMESPACE_STD
0028
0029 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned __x) _NOEXCEPT {
0030   return __builtin_ctz(__x);
0031 }
0032
0033 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long __x) _NOEXCEPT {
0034   return __builtin_ctzl(__x);
0035 }
0036
0037 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long long __x) _NOEXCEPT {
0038   return __builtin_ctzll(__x);
0039 }
0040
0041 template <class _Tp>
0042 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countr_zero(_Tp __t) _NOEXCEPT {
0043 #if __has_builtin(__builtin_ctzg)
0044   return __builtin_ctzg(__t, numeric_limits<_Tp>::digits);
0045 #else  // __has_builtin(__builtin_ctzg)
0046   if (__t == 0)
0047     return numeric_limits<_Tp>::digits;
0048   if (sizeof(_Tp) <= sizeof(unsigned int))
0049     return std::__libcpp_ctz(static_cast<unsigned int>(__t));
0050   else if (sizeof(_Tp) <= sizeof(unsigned long))
0051     return std::__libcpp_ctz(static_cast<unsigned long>(__t));
0052   else if (sizeof(_Tp) <= sizeof(unsigned long long))
0053     return std::__libcpp_ctz(static_cast<unsigned long long>(__t));
0054   else {
0055     int __ret                      = 0;
0056     const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
0057     while (static_cast<unsigned long long>(__t) == 0uLL) {
0058       __ret += __ulldigits;
0059       __t >>= __ulldigits;
0060     }
0061     return __ret + std::__libcpp_ctz(static_cast<unsigned long long>(__t));
0062   }
0063 #endif // __has_builtin(__builtin_ctzg)
0064 }
0065
0066 #if _LIBCPP_STD_VER >= 20
0067
0068 template <__libcpp_unsigned_integer _Tp>
0069 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
0070   return std::__countr_zero(__t);
0071 }
0072
0073 template <__libcpp_unsigned_integer _Tp>
0074 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countr_one(_Tp __t) noexcept {
0075   return __t != numeric_limits<_Tp>::max() ? std::countr_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
0076 }
0077
0078 #endif // _LIBCPP_STD_VER >= 20
0079
0080 _LIBCPP_END_NAMESPACE_STD
0081
0082 _LIBCPP_POP_MACROS
0083
0084 #endif // _LIBCPP___CXX03___BIT_COUNTR_H