xref: /openbsd-src/gnu/llvm/libcxx/include/__bit/countl.h (revision 4bdff4bed0e3d54e55670334c7d0077db4170f86)

//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#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

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_clz(unsigned __x)           _NOEXCEPT { return __builtin_clz(__x); }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_clz(unsigned long __x)      _NOEXCEPT { return __builtin_clzl(__x); }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_clz(unsigned long long __x) _NOEXCEPT { return __builtin_clzll(__x); }

#  ifndef _LIBCPP_HAS_NO_INT128
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_clz(__uint128_t __x) _NOEXCEPT {
  // 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 // _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 (__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::__rotr(__t, __ulldigits);
            if ((__iter = std::__countl_zero(static_cast<unsigned long long>(__t))) != __ulldigits)
                break;
            __ret += __iter;
            }
        return __ret + __iter;
    }
}

#if _LIBCPP_STD_VER >= 20

template <__libcpp_unsigned_integer _Tp>
_LIBCPP_HIDE_FROM_ABI constexpr int countl_zero(_Tp __t) noexcept {
  return std::__countl_zero(__t);
}

template <__libcpp_unsigned_integer _Tp>
_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