libcxx/include/__bit/countr.h

   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___BIT_COUNTR_H
  13 #define _LIBCPP___BIT_COUNTR_H
  14
  15 #include <__bit/rotate.h>
  16 #include <__concepts/arithmetic.h>
  17 #include <__config>
  18 #include <limits>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_PUSH_MACROS
  25 #include <__undef_macros>
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned __x) _NOEXCEPT {
  30   return __builtin_ctz(__x);
  31 }
  32
  33 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long __x) _NOEXCEPT {
  34   return __builtin_ctzl(__x);
  35 }
  36
  37 [[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_ctz(unsigned long long __x) _NOEXCEPT {
  38   return __builtin_ctzll(__x);
  39 }
  40
  41 template <class _Tp>
  42 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countr_zero(_Tp __t) _NOEXCEPT {
  43 #if __has_builtin(__builtin_ctzg)
  44   return __builtin_ctzg(__t, numeric_limits<_Tp>::digits);
  45 #else  // __has_builtin(__builtin_ctzg)
  46   if (__t == 0)
  47     return numeric_limits<_Tp>::digits;
  48   if (sizeof(_Tp) <= sizeof(unsigned int))
  49     return std::__libcpp_ctz(static_cast<unsigned int>(__t));
  50   else if (sizeof(_Tp) <= sizeof(unsigned long))
  51     return std::__libcpp_ctz(static_cast<unsigned long>(__t));
  52   else if (sizeof(_Tp) <= sizeof(unsigned long long))
  53     return std::__libcpp_ctz(static_cast<unsigned long long>(__t));
  54   else {
  55     int __ret                      = 0;
  56     const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
  57     while (static_cast<unsigned long long>(__t) == 0uLL) {
  58       __ret += __ulldigits;
  59       __t >>= __ulldigits;
  60     }
  61     return __ret + std::__libcpp_ctz(static_cast<unsigned long long>(__t));
  62   }
  63 #endif // __has_builtin(__builtin_ctzg)
  64 }
  65
  66 #if _LIBCPP_STD_VER >= 20
  67
  68 template <__libcpp_unsigned_integer _Tp>
  69 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
  70   return std::__countr_zero(__t);
  71 }
  72
  73 template <__libcpp_unsigned_integer _Tp>
  74 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countr_one(_Tp __t) noexcept {
  75   return __t != numeric_limits<_Tp>::max() ? std::countr_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
  76 }
  77
  78 #endif // _LIBCPP_STD_VER >= 20
  79
  80 _LIBCPP_END_NAMESPACE_STD
  81
  82 _LIBCPP_POP_MACROS
  83
  84 #endif // _LIBCPP___BIT_COUNTR_H