mirror of
https://github.com/llvm/llvm-project.git
synced 2025-04-28 06:56:06 +00:00
d78ca7324c
This "bug" was probably not noticed because it doesn't affect any integer type we currently support. It requires integers with more than 2x the size of `unsigned long long`. However, with such types, the algorithm used to break down the large integer into groups of size `unsigned long long` didn't work because we rotated in the wrong direction. For example, the 256 bit number (1 << 255) would yield the wrong answer when used with the algorithm before this patch. In particular, note that the current rotation happens to work for 128 bit integers because it just swaps the halves in this case. Differential Revision: https://reviews.llvm.org/D134625 Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
60 lines
1.8 KiB
C++
60 lines
1.8 KiB
C++
//===----------------------------------------------------------------------===//
|
|
//
|
|
// 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_ROTATE_H
|
|
#define _LIBCPP___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_BEGIN_NAMESPACE_STD
|
|
|
|
template <class _Tp>
|
|
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __rotr(_Tp __t, int __cnt) _NOEXCEPT {
|
|
static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__rotr requires an unsigned integer type");
|
|
const unsigned int __dig = numeric_limits<_Tp>::digits;
|
|
if ((__cnt % __dig) == 0)
|
|
return __t;
|
|
|
|
if (__cnt < 0) {
|
|
__cnt *= -1;
|
|
return (__t << (__cnt % __dig)) | (__t >> (__dig - (__cnt % __dig))); // rotr with negative __cnt is similar to rotl
|
|
}
|
|
|
|
return (__t >> (__cnt % __dig)) | (__t << (__dig - (__cnt % __dig)));
|
|
}
|
|
|
|
template <class _Tp>
|
|
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __rotl(_Tp __t, int __cnt) _NOEXCEPT {
|
|
return std::__rotr(__t, -__cnt);
|
|
}
|
|
|
|
#if _LIBCPP_STD_VER >= 20
|
|
|
|
template <__libcpp_unsigned_integer _Tp>
|
|
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp rotl(_Tp __t, int __cnt) noexcept {
|
|
return std::__rotl(__t, __cnt);
|
|
}
|
|
|
|
template <__libcpp_unsigned_integer _Tp>
|
|
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp rotr(_Tp __t, int __cnt) noexcept {
|
|
return std::__rotr(__t, __cnt);
|
|
}
|
|
|
|
#endif // _LIBCPP_STD_VER >= 20
|
|
|
|
_LIBCPP_END_NAMESPACE_STD
|
|
|
|
#endif // _LIBCPP___BIT_ROTATE_H
|