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