libcxx/include/__bit/popcount.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_popcountg 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_popcountg.
  11
  12 #ifndef _LIBCPP___BIT_POPCOUNT_H
  13 #define _LIBCPP___BIT_POPCOUNT_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 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_popcount(unsigned __x) _NOEXCEPT {
  30   return __builtin_popcount(__x);
  31 }
  32
  33 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_popcount(unsigned long __x) _NOEXCEPT {
  34   return __builtin_popcountl(__x);
  35 }
  36
  37 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_popcount(unsigned long long __x) _NOEXCEPT {
  38   return __builtin_popcountll(__x);
  39 }
  40
  41 #if _LIBCPP_STD_VER >= 20
  42
  43 template <__libcpp_unsigned_integer _Tp>
  44 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int popcount(_Tp __t) noexcept {
  45 #  if __has_builtin(__builtin_popcountg)
  46   return __builtin_popcountg(__t);
  47 #  else  // __has_builtin(__builtin_popcountg)
  48   if (sizeof(_Tp) <= sizeof(unsigned int))
  49     return std::__libcpp_popcount(static_cast<unsigned int>(__t));
  50   else if (sizeof(_Tp) <= sizeof(unsigned long))
  51     return std::__libcpp_popcount(static_cast<unsigned long>(__t));
  52   else if (sizeof(_Tp) <= sizeof(unsigned long long))
  53     return std::__libcpp_popcount(static_cast<unsigned long long>(__t));
  54   else {
  55     int __ret = 0;
  56     while (__t != 0) {
  57       __ret += std::__libcpp_popcount(static_cast<unsigned long long>(__t));
  58       __t >>= numeric_limits<unsigned long long>::digits;
  59     }
  60     return __ret;
  61   }
  62 #  endif // __has_builtin(__builtin_popcountg)
  63 }
  64
  65 #endif // _LIBCPP_STD_VER >= 20
  66
  67 _LIBCPP_END_NAMESPACE_STD
  68
  69 _LIBCPP_POP_MACROS
  70
  71 #endif // _LIBCPP___BIT_POPCOUNT_H