libcxx/include/__numeric/gcd_lcm.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___NUMERIC_GCD_LCM_H
  11 #define _LIBCPP___NUMERIC_GCD_LCM_H
  12
  13 #include <__config>
  14 #include <__debug>
  15 #include <limits>
  16 #include <type_traits>
  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 #if _LIBCPP_STD_VER > 14
  28
  29 template <typename _Result, typename _Source, bool _IsSigned = is_signed<_Source>::value> struct __ct_abs;
  30
  31 template <typename _Result, typename _Source>
  32 struct __ct_abs<_Result, _Source, true> {
  33     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  34     _Result operator()(_Source __t) const noexcept
  35     {
  36         if (__t >= 0) return __t;
  37         if (__t == numeric_limits<_Source>::min()) return -static_cast<_Result>(__t);
  38         return -__t;
  39     }
  40 };
  41
  42 template <typename _Result, typename _Source>
  43 struct __ct_abs<_Result, _Source, false> {
  44     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  45     _Result operator()(_Source __t) const noexcept { return __t; }
  46 };
  47
  48
  49 template<class _Tp>
  50 _LIBCPP_CONSTEXPR _LIBCPP_HIDDEN
  51 _Tp __gcd(_Tp __m, _Tp __n)
  52 {
  53     static_assert((!is_signed<_Tp>::value), "");
  54     return __n == 0 ? __m : _VSTD::__gcd<_Tp>(__n, __m % __n);
  55 }
  56
  57 template<class _Tp, class _Up>
  58 _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  59 common_type_t<_Tp,_Up>
  60 gcd(_Tp __m, _Up __n)
  61 {
  62     static_assert((is_integral<_Tp>::value && is_integral<_Up>::value), "Arguments to gcd must be integer types");
  63     static_assert((!is_same<typename remove_cv<_Tp>::type, bool>::value), "First argument to gcd cannot be bool" );
  64     static_assert((!is_same<typename remove_cv<_Up>::type, bool>::value), "Second argument to gcd cannot be bool" );
  65     using _Rp = common_type_t<_Tp,_Up>;
  66     using _Wp = make_unsigned_t<_Rp>;
  67     return static_cast<_Rp>(_VSTD::__gcd(
  68         static_cast<_Wp>(__ct_abs<_Rp, _Tp>()(__m)),
  69         static_cast<_Wp>(__ct_abs<_Rp, _Up>()(__n))));
  70 }
  71
  72 template<class _Tp, class _Up>
  73 _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  74 common_type_t<_Tp,_Up>
  75 lcm(_Tp __m, _Up __n)
  76 {
  77     static_assert((is_integral<_Tp>::value && is_integral<_Up>::value), "Arguments to lcm must be integer types");
  78     static_assert((!is_same<typename remove_cv<_Tp>::type, bool>::value), "First argument to lcm cannot be bool" );
  79     static_assert((!is_same<typename remove_cv<_Up>::type, bool>::value), "Second argument to lcm cannot be bool" );
  80     if (__m == 0 || __n == 0)
  81         return 0;
  82
  83     using _Rp = common_type_t<_Tp,_Up>;
  84     _Rp __val1 = __ct_abs<_Rp, _Tp>()(__m) / _VSTD::gcd(__m, __n);
  85     _Rp __val2 = __ct_abs<_Rp, _Up>()(__n);
  86     _LIBCPP_ASSERT((numeric_limits<_Rp>::max() / __val1 > __val2), "Overflow in lcm");
  87     return __val1 * __val2;
  88 }
  89
  90 #endif // _LIBCPP_STD_VER
  91
  92 _LIBCPP_END_NAMESPACE_STD
  93
  94 _LIBCPP_POP_MACROS
  95
  96 #endif // _LIBCPP___NUMERIC_GCD_LCM_H