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>
  34 struct __ct_abs;
  35
  36 template <typename _Result, typename _Source>
  37 struct __ct_abs<_Result, _Source, true> {
  38   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _Result operator()(_Source __t) const noexcept {
  39     if (__t >= 0)
  40       return __t;
  41     if (__t == numeric_limits<_Source>::min())
  42       return -static_cast<_Result>(__t);
  43     return -__t;
  44   }
  45 };
  46
  47 template <typename _Result, typename _Source>
  48 struct __ct_abs<_Result, _Source, false> {
  49   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _Result operator()(_Source __t) const noexcept { return __t; }
  50 };
  51
  52 template <class _Tp>
  53 _LIBCPP_CONSTEXPR _LIBCPP_HIDDEN _Tp __gcd(_Tp __m, _Tp __n) {
  54   static_assert((!is_signed<_Tp>::value), "");
  55   return __n == 0 ? __m : std::__gcd<_Tp>(__n, __m % __n);
  56 }
  57
  58 template <class _Tp, class _Up>
  59 _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI common_type_t<_Tp, _Up> gcd(_Tp __m, _Up __n) {
  60   static_assert((is_integral<_Tp>::value && is_integral<_Up>::value), "Arguments to gcd must be integer types");
  61   static_assert((!is_same<__remove_cv_t<_Tp>, bool>::value), "First argument to gcd cannot be bool");
  62   static_assert((!is_same<__remove_cv_t<_Up>, bool>::value), "Second argument to gcd cannot be bool");
  63   using _Rp = common_type_t<_Tp, _Up>;
  64   using _Wp = make_unsigned_t<_Rp>;
  65   return static_cast<_Rp>(
  66       std::__gcd(static_cast<_Wp>(__ct_abs<_Rp, _Tp>()(__m)), static_cast<_Wp>(__ct_abs<_Rp, _Up>()(__n))));
  67 }
  68
  69 template <class _Tp, class _Up>
  70 _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI common_type_t<_Tp, _Up> lcm(_Tp __m, _Up __n) {
  71   static_assert((is_integral<_Tp>::value && is_integral<_Up>::value), "Arguments to lcm must be integer types");
  72   static_assert((!is_same<__remove_cv_t<_Tp>, bool>::value), "First argument to lcm cannot be bool");
  73   static_assert((!is_same<__remove_cv_t<_Up>, bool>::value), "Second argument to lcm cannot be bool");
  74   if (__m == 0 || __n == 0)
  75     return 0;
  76
  77   using _Rp  = common_type_t<_Tp, _Up>;
  78   _Rp __val1 = __ct_abs<_Rp, _Tp>()(__m) / std::gcd(__m, __n);
  79   _Rp __val2 = __ct_abs<_Rp, _Up>()(__n);
  80   _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN((numeric_limits<_Rp>::max() / __val1 > __val2), "Overflow in lcm");
  81   return __val1 * __val2;
  82 }
  83
  84 #endif // _LIBCPP_STD_VER
  85
  86 _LIBCPP_END_NAMESPACE_STD
  87
  88 _LIBCPP_POP_MACROS
  89
  90 #endif // _LIBCPP___NUMERIC_GCD_LCM_H