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 28 int __libcpp_clz(unsigned __x) _NOEXCEPT { return __builtin_clz(__x); } 29 30 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR 31 int __libcpp_clz(unsigned long __x) _NOEXCEPT { return __builtin_clzl(__x); } 32 33 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _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_NODISCARD_EXT _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_NODISCARD_EXT _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