xref: /freebsd/contrib/llvm-project/libcxx/include/__bit/countl.h (revision 7ef62cebc2f965b0f640263e179276928885e33d)
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 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
28 int __libcpp_clz(unsigned __x)           _NOEXCEPT { return __builtin_clz(__x); }
29 
30 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
31 int __libcpp_clz(unsigned long __x)      _NOEXCEPT { return __builtin_clzl(__x); }
32 
33 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
34 int __libcpp_clz(unsigned long long __x) _NOEXCEPT { return __builtin_clzll(__x); }
35 
36 #  ifndef _LIBCPP_HAS_NO_INT128
37 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
38 int __libcpp_clz(__uint128_t __x) _NOEXCEPT {
39   // The function is written in this form due to C++ constexpr limitations.
40   // The algorithm:
41   // - Test whether any bit in the high 64-bits is set
42   // - No bits set:
43   //   - The high 64-bits contain 64 leading zeros,
44   //   - Add the result of the low 64-bits.
45   // - Any bits set:
46   //   - The number of leading zeros of the input is the number of leading
47   //     zeros in the high 64-bits.
48   return ((__x >> 64) == 0)
49            ? (64 + __builtin_clzll(static_cast<unsigned long long>(__x)))
50            : __builtin_clzll(static_cast<unsigned long long>(__x >> 64));
51 }
52 #  endif // _LIBCPP_HAS_NO_INT128
53 
54 template<class _Tp>
55 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
56 int __countl_zero(_Tp __t) _NOEXCEPT
57 {
58     static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__countl_zero requires an unsigned integer type");
59     if (__t == 0)
60         return numeric_limits<_Tp>::digits;
61 
62     if      (sizeof(_Tp) <= sizeof(unsigned int))
63         return std::__libcpp_clz(static_cast<unsigned int>(__t))
64               - (numeric_limits<unsigned int>::digits - numeric_limits<_Tp>::digits);
65     else if (sizeof(_Tp) <= sizeof(unsigned long))
66         return std::__libcpp_clz(static_cast<unsigned long>(__t))
67               - (numeric_limits<unsigned long>::digits - numeric_limits<_Tp>::digits);
68     else if (sizeof(_Tp) <= sizeof(unsigned long long))
69         return std::__libcpp_clz(static_cast<unsigned long long>(__t))
70               - (numeric_limits<unsigned long long>::digits - numeric_limits<_Tp>::digits);
71     else
72     {
73         int __ret = 0;
74         int __iter = 0;
75         const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
76         while (true) {
77             __t = std::__rotr(__t, __ulldigits);
78             if ((__iter = std::__countl_zero(static_cast<unsigned long long>(__t))) != __ulldigits)
79                 break;
80             __ret += __iter;
81             }
82         return __ret + __iter;
83     }
84 }
85 
86 #if _LIBCPP_STD_VER >= 20
87 
88 template <__libcpp_unsigned_integer _Tp>
89 _LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
90   return std::__countl_zero(__t);
91 }
92 
93 template <__libcpp_unsigned_integer _Tp>
94 _LIBCPP_HIDE_FROM_ABI constexpr int countl_one(_Tp __t) noexcept {
95   return __t != numeric_limits<_Tp>::max() ? std::countl_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
96 }
97 
98 #endif // _LIBCPP_STD_VER >= 20
99 
100 _LIBCPP_END_NAMESPACE_STD
101 
102 _LIBCPP_POP_MACROS
103 
104 #endif // _LIBCPP___BIT_COUNTL_H
105