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