libcxx/include/__bit/countl.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_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::__rotl(__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