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_clzg 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_clzg.
11
12#ifndef _LIBCPP___BIT_COUNTL_H
13#define _LIBCPP___BIT_COUNTL_H
14
15#include <__bit/rotate.h>
16#include <__concepts/arithmetic.h>
17#include <__config>
18#include <__type_traits/is_unsigned_integer.h>
19#include <limits>
20
21#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
22# pragma GCC system_header
23#endif
24
25_LIBCPP_PUSH_MACROS
26#include <__undef_macros>
27
28_LIBCPP_BEGIN_NAMESPACE_STD
29
30_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned __x) _NOEXCEPT {
31 return __builtin_clz(__x);
32}
33
34_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long __x) _NOEXCEPT {
35 return __builtin_clzl(__x);
36}
37
38_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long long __x) _NOEXCEPT {
39 return __builtin_clzll(__x);
40}
41
42#ifndef _LIBCPP_HAS_NO_INT128
43inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(__uint128_t __x) _NOEXCEPT {
44# if __has_builtin(__builtin_clzg)
45 return __builtin_clzg(__x);
46# else
47 // The function is written in this form due to C++ constexpr limitations.
48 // The algorithm:
49 // - Test whether any bit in the high 64-bits is set
50 // - No bits set:
51 // - The high 64-bits contain 64 leading zeros,
52 // - Add the result of the low 64-bits.
53 // - Any bits set:
54 // - The number of leading zeros of the input is the number of leading
55 // zeros in the high 64-bits.
56 return ((__x >> 64) == 0) ? (64 + __builtin_clzll(static_cast<unsigned long long>(__x)))
57 : __builtin_clzll(static_cast<unsigned long long>(__x >> 64));
58# endif
59}
60#endif // _LIBCPP_HAS_NO_INT128
61
62template <class _Tp>
63_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countl_zero(_Tp __t) _NOEXCEPT {
64 static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__countl_zero requires an unsigned integer type");
65#if __has_builtin(__builtin_clzg)
66 return __builtin_clzg(__t, numeric_limits<_Tp>::digits);
67#else // __has_builtin(__builtin_clzg)
68 if (__t == 0)
69 return numeric_limits<_Tp>::digits;
70
71 if (sizeof(_Tp) <= sizeof(unsigned int))
72 return std::__libcpp_clz(static_cast<unsigned int>(__t)) -
73 (numeric_limits<unsigned int>::digits - numeric_limits<_Tp>::digits);
74 else if (sizeof(_Tp) <= sizeof(unsigned long))
75 return std::__libcpp_clz(static_cast<unsigned long>(__t)) -
76 (numeric_limits<unsigned long>::digits - numeric_limits<_Tp>::digits);
77 else if (sizeof(_Tp) <= sizeof(unsigned long long))
78 return std::__libcpp_clz(static_cast<unsigned long long>(__t)) -
79 (numeric_limits<unsigned long long>::digits - numeric_limits<_Tp>::digits);
80 else {
81 int __ret = 0;
82 int __iter = 0;
83 const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
84 while (true) {
85 __t = std::__rotl(__t, __ulldigits);
86 if ((__iter = std::__countl_zero(static_cast<unsigned long long>(__t))) != __ulldigits)
87 break;
88 __ret += __iter;
89 }
90 return __ret + __iter;
91 }
92#endif // __has_builtin(__builtin_clzg)
93}
94
95#if _LIBCPP_STD_VER >= 20
96
97template <__libcpp_unsigned_integer _Tp>
98[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
99 return std::__countl_zero(__t);
100}
101
102template <__libcpp_unsigned_integer _Tp>
103[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countl_one(_Tp __t) noexcept {
104 return __t != numeric_limits<_Tp>::max() ? std::countl_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
105}
106
107#endif // _LIBCPP_STD_VER >= 20
108
109_LIBCPP_END_NAMESPACE_STD
110
111_LIBCPP_POP_MACROS
112
113#endif // _LIBCPP___BIT_COUNTL_H
114