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 <__assert>
  14 #include <__config>
  15 #include <__type_traits/common_type.h>
  16 #include <__type_traits/is_integral.h>
  17 #include <__type_traits/is_same.h>
  18 #include <__type_traits/is_signed.h>
  19 #include <__type_traits/make_unsigned.h>
  20 #include <limits>
  21
  22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  23 #  pragma GCC system_header
  24 #endif
  25
  26 _LIBCPP_PUSH_MACROS
  27 #include <__undef_macros>
  28
  29 _LIBCPP_BEGIN_NAMESPACE_STD
  30
  31 #if _LIBCPP_STD_VER >= 17
  32
  33 template <typename _Result, typename _Source, bool _IsSigned = is_signed<_Source>::value> struct __ct_abs;
  34
  35 template <typename _Result, typename _Source>
  36 struct __ct_abs<_Result, _Source, true> {
  37     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  38     _Result operator()(_Source __t) const noexcept
  39     {
  40         if (__t >= 0) return __t;
  41         if (__t == numeric_limits<_Source>::min()) return -static_cast<_Result>(__t);
  42         return -__t;
  43     }
  44 };
  45
  46 template <typename _Result, typename _Source>
  47 struct __ct_abs<_Result, _Source, false> {
  48     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  49     _Result operator()(_Source __t) const noexcept { return __t; }
  50 };
  51
  52
  53 template<class _Tp>
  54 _LIBCPP_CONSTEXPR _LIBCPP_HIDDEN
  55 _Tp __gcd(_Tp __m, _Tp __n)
  56 {
  57     static_assert((!is_signed<_Tp>::value), "");
  58     return __n == 0 ? __m : _VSTD::__gcd<_Tp>(__n, __m % __n);
  59 }
  60
  61 template<class _Tp, class _Up>
  62 _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  63 common_type_t<_Tp,_Up>
  64 gcd(_Tp __m, _Up __n)
  65 {
  66     static_assert((is_integral<_Tp>::value && is_integral<_Up>::value), "Arguments to gcd must be integer types");
  67     static_assert((!is_same<__remove_cv_t<_Tp>, bool>::value), "First argument to gcd cannot be bool" );
  68     static_assert((!is_same<__remove_cv_t<_Up>, bool>::value), "Second argument to gcd cannot be bool" );
  69     using _Rp = common_type_t<_Tp,_Up>;
  70     using _Wp = make_unsigned_t<_Rp>;
  71     return static_cast<_Rp>(_VSTD::__gcd(
  72         static_cast<_Wp>(__ct_abs<_Rp, _Tp>()(__m)),
  73         static_cast<_Wp>(__ct_abs<_Rp, _Up>()(__n))));
  74 }
  75
  76 template<class _Tp, class _Up>
  77 _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
  78 common_type_t<_Tp,_Up>
  79 lcm(_Tp __m, _Up __n)
  80 {
  81     static_assert((is_integral<_Tp>::value && is_integral<_Up>::value), "Arguments to lcm must be integer types");
  82     static_assert((!is_same<__remove_cv_t<_Tp>, bool>::value), "First argument to lcm cannot be bool" );
  83     static_assert((!is_same<__remove_cv_t<_Up>, bool>::value), "Second argument to lcm cannot be bool" );
  84     if (__m == 0 || __n == 0)
  85         return 0;
  86
  87     using _Rp = common_type_t<_Tp,_Up>;
  88     _Rp __val1 = __ct_abs<_Rp, _Tp>()(__m) / _VSTD::gcd(__m, __n);
  89     _Rp __val2 = __ct_abs<_Rp, _Up>()(__n);
  90     _LIBCPP_ASSERT_UNCATEGORIZED((numeric_limits<_Rp>::max() / __val1 > __val2), "Overflow in lcm");
  91     return __val1 * __val2;
  92 }
  93
  94 #endif // _LIBCPP_STD_VER
  95
  96 _LIBCPP_END_NAMESPACE_STD
  97
  98 _LIBCPP_POP_MACROS
  99
 100 #endif // _LIBCPP___NUMERIC_GCD_LCM_H