libcxx/include/__bit/countr.h

   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_COUNTR_H
  10 #define _LIBCPP___BIT_COUNTR_H
  11
  12 #include <__bit/rotate.h>
  13 #include <__concepts/arithmetic.h>
  14 #include <__config>
  15 #include <limits>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_PUSH_MACROS
  22 #include <__undef_macros>
  23
  24 _LIBCPP_BEGIN_NAMESPACE_STD
  25
  26 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
  27 int __libcpp_ctz(unsigned __x)           _NOEXCEPT { return __builtin_ctz(__x); }
  28
  29 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
  30 int __libcpp_ctz(unsigned long __x)      _NOEXCEPT { return __builtin_ctzl(__x); }
  31
  32 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
  33 int __libcpp_ctz(unsigned long long __x) _NOEXCEPT { return __builtin_ctzll(__x); }
  34
  35 #if _LIBCPP_STD_VER >= 20
  36
  37 template <__libcpp_unsigned_integer _Tp>
  38 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
  39   if (__t == 0)
  40     return numeric_limits<_Tp>::digits;
  41
  42   if (sizeof(_Tp) <= sizeof(unsigned int))
  43     return std::__libcpp_ctz(static_cast<unsigned int>(__t));
  44   else if (sizeof(_Tp) <= sizeof(unsigned long))
  45     return std::__libcpp_ctz(static_cast<unsigned long>(__t));
  46   else if (sizeof(_Tp) <= sizeof(unsigned long long))
  47     return std::__libcpp_ctz(static_cast<unsigned long long>(__t));
  48   else {
  49     int __ret = 0;
  50     const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
  51     while (static_cast<unsigned long long>(__t) == 0uLL) {
  52       __ret += __ulldigits;
  53       __t >>= __ulldigits;
  54     }
  55     return __ret + std::__libcpp_ctz(static_cast<unsigned long long>(__t));
  56   }
  57 }
  58
  59 template <__libcpp_unsigned_integer _Tp>
  60 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int countr_one(_Tp __t) noexcept {
  61   return __t != numeric_limits<_Tp>::max() ? std::countr_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
  62 }
  63
  64 #endif // _LIBCPP_STD_VER >= 20
  65
  66 _LIBCPP_END_NAMESPACE_STD
  67
  68 _LIBCPP_POP_MACROS
  69
  70 #endif // _LIBCPP___BIT_COUNTR_H