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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// TODO: __builtin_clzg is available since Clang 19 and GCC 14. When support for older versions is dropped, we can
// refactor this code to exclusively use __builtin_clzg.
#ifndef _LIBCPP___BIT_COUNTL_H
#define _LIBCPP___BIT_COUNTL_H
#include <__bit/rotate.h>
#include <__concepts/arithmetic.h>
#include <__config>
#include <__type_traits/is_unsigned_integer.h>
#include <limits>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_PUSH_MACROS
#include <__undef_macros>
_LIBCPP_BEGIN_NAMESPACE_STD
_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned __x) _NOEXCEPT {
return __builtin_clz(__x);
}
_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long __x) _NOEXCEPT {
return __builtin_clzl(__x);
}
_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(unsigned long long __x) _NOEXCEPT {
return __builtin_clzll(__x);
}
#ifndef _LIBCPP_HAS_NO_INT128
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_clz(__uint128_t __x) _NOEXCEPT {
# if __has_builtin(__builtin_clzg)
return __builtin_clzg(__x);
# else
// The function is written in this form due to C++ constexpr limitations.
// The algorithm:
// - Test whether any bit in the high 64-bits is set
// - No bits set:
// - The high 64-bits contain 64 leading zeros,
// - Add the result of the low 64-bits.
// - Any bits set:
// - The number of leading zeros of the input is the number of leading
// zeros in the high 64-bits.
return ((__x >> 64) == 0) ? (64 + __builtin_clzll(static_cast<unsigned long long>(__x)))
: __builtin_clzll(static_cast<unsigned long long>(__x >> 64));
# endif
}
#endif // _LIBCPP_HAS_NO_INT128
template <class _Tp>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countl_zero(_Tp __t) _NOEXCEPT {
static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__countl_zero requires an unsigned integer type");
#if __has_builtin(__builtin_clzg)
return __builtin_clzg(__t, numeric_limits<_Tp>::digits);
#else // __has_builtin(__builtin_clzg)
if (__t == 0)
return numeric_limits<_Tp>::digits;
if (sizeof(_Tp) <= sizeof(unsigned int))
return std::__libcpp_clz(static_cast<unsigned int>(__t)) -
(numeric_limits<unsigned int>::digits - numeric_limits<_Tp>::digits);
else if (sizeof(_Tp) <= sizeof(unsigned long))
return std::__libcpp_clz(static_cast<unsigned long>(__t)) -
(numeric_limits<unsigned long>::digits - numeric_limits<_Tp>::digits);
else if (sizeof(_Tp) <= sizeof(unsigned long long))
return std::__libcpp_clz(static_cast<unsigned long long>(__t)) -
(numeric_limits<unsigned long long>::digits - numeric_limits<_Tp>::digits);
else {
int __ret = 0;
int __iter = 0;
const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
while (true) {
__t = std::__rotl(__t, __ulldigits);
if ((__iter = std::__countl_zero(static_cast<unsigned long long>(__t))) != __ulldigits)
break;
__ret += __iter;
}
return __ret + __iter;
}
#endif // __has_builtin(__builtin_clzg)
}
#if _LIBCPP_STD_VER >= 20
template <__libcpp_unsigned_integer _Tp>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
return std::__countl_zero(__t);
}
template <__libcpp_unsigned_integer _Tp>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countl_one(_Tp __t) noexcept {
return __t != numeric_limits<_Tp>::max() ? std::countl_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
}
#endif // _LIBCPP_STD_VER >= 20
_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS
#endif // _LIBCPP___BIT_COUNTL_H
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