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
29inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_popcount(unsigned __x) _NOEXCEPT {
30 return __builtin_popcount(__x);
31}
32
33inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_popcount(unsigned long __x) _NOEXCEPT {
34 return __builtin_popcountl(__x);
35}
36
37inline _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
43template <__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
72