libcxx/include/__bit/rotate.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_ROTATE_H
  10 #define _LIBCPP___BIT_ROTATE_H
  11
  12 #include <__concepts/arithmetic.h>
  13 #include <__config>
  14 #include <__type_traits/is_unsigned_integer.h>
  15 #include <limits>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 // Writing two full functions for rotl and rotr makes it easier for the compiler
  24 // to optimize the code. On x86 this function becomes the ROL instruction and
  25 // the rotr function becomes the ROR instruction.
  26 template <class _Tp>
  27 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __rotl(_Tp __x, int __s) _NOEXCEPT {
  28   static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__rotl requires an unsigned integer type");
  29   const int __n = numeric_limits<_Tp>::digits;
  30   int __r       = __s % __n;
  31
  32   if (__r == 0)
  33     return __x;
  34
  35   if (__r > 0)
  36     return (__x << __r) | (__x >> (__n - __r));
  37
  38   return (__x >> -__r) | (__x << (__n + __r));
  39 }
  40
  41 template <class _Tp>
  42 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __rotr(_Tp __x, int __s) _NOEXCEPT {
  43   static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__rotr requires an unsigned integer type");
  44   const int __n = numeric_limits<_Tp>::digits;
  45   int __r       = __s % __n;
  46
  47   if (__r == 0)
  48     return __x;
  49
  50   if (__r > 0)
  51     return (__x >> __r) | (__x << (__n - __r));
  52
  53   return (__x << -__r) | (__x >> (__n + __r));
  54 }
  55
  56 #if _LIBCPP_STD_VER >= 20
  57
  58 template <__libcpp_unsigned_integer _Tp>
  59 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp rotl(_Tp __t, int __cnt) noexcept {
  60   return std::__rotl(__t, __cnt);
  61 }
  62
  63 template <__libcpp_unsigned_integer _Tp>
  64 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp rotr(_Tp __t, int __cnt) noexcept {
  65   return std::__rotr(__t, __cnt);
  66 }
  67
  68 #endif // _LIBCPP_STD_VER >= 20
  69
  70 _LIBCPP_END_NAMESPACE_STD
  71
  72 #endif // _LIBCPP___BIT_ROTATE_H