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___RANDOM_LOG2_H
10 #define _LIBCPP___RANDOM_LOG2_H
11 
12 #include <__config>
13 #include <__type_traits/conditional.h>
14 #include <cstddef>
15 
16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17 #  pragma GCC system_header
18 #endif
19 
20 _LIBCPP_BEGIN_NAMESPACE_STD
21 
22 template <class _UIntType, _UIntType _Xp, size_t _Rp>
23 struct __log2_imp;
24 
25 template <unsigned long long _Xp, size_t _Rp>
26 struct __log2_imp<unsigned long long, _Xp, _Rp> {
27   static const size_t value =
28       _Xp & ((unsigned long long)(1) << _Rp) ? _Rp : __log2_imp<unsigned long long, _Xp, _Rp - 1>::value;
29 };
30 
31 template <unsigned long long _Xp>
32 struct __log2_imp<unsigned long long, _Xp, 0> {
33   static const size_t value = 0;
34 };
35 
36 template <size_t _Rp>
37 struct __log2_imp<unsigned long long, 0, _Rp> {
38   static const size_t value = _Rp + 1;
39 };
40 
41 #ifndef _LIBCPP_HAS_NO_INT128
42 
43 template <__uint128_t _Xp, size_t _Rp>
44 struct __log2_imp<__uint128_t, _Xp, _Rp> {
45   static const size_t value =
46       (_Xp >> 64) ? (64 + __log2_imp<unsigned long long, (_Xp >> 64), 63>::value)
47                   : __log2_imp<unsigned long long, _Xp, 63>::value;
48 };
49 
50 #endif // _LIBCPP_HAS_NO_INT128
51 
52 template <class _UIntType, _UIntType _Xp>
53 struct __log2 {
54   static const size_t value = __log2_imp<
55 #ifndef _LIBCPP_HAS_NO_INT128
56       __conditional_t<sizeof(_UIntType) <= sizeof(unsigned long long), unsigned long long, __uint128_t>,
57 #else
58       unsigned long long,
59 #endif // _LIBCPP_HAS_NO_INT128
60       _Xp,
61       sizeof(_UIntType) * __CHAR_BIT__ - 1>::value;
62 };
63 
64 _LIBCPP_END_NAMESPACE_STD
65 
66 #endif // _LIBCPP___RANDOM_LOG2_H
67