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SFINAE out duration converting constructor if the constructor would otherwise cause a ratio compile-time overflow. This fixes LWG 2094.

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git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@189722 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Howard Hinnant
2013-08-31 16:51:56 +00:00
parent 9e9d076879
commit 713f4db2e5
3 changed files with 39 additions and 3 deletions
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36
include/chrono
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@@ -409,6 +409,37 @@ class _LIBCPP_TYPE_VIS_ONLY duration
static_assert(!__is_duration<_Rep>::value, "A duration representation can not be a duration");
static_assert(__is_ratio<_Period>::value, "Second template parameter of duration must be a std::ratio");
static_assert(_Period::num > 0, "duration period must be positive");
template <class _R1, class _R2>
struct __no_overflow
{
private:
static const intmax_t __gcd_n1_n2 = __static_gcd<_R1::num, _R2::num>::value;
static const intmax_t __gcd_d1_d2 = __static_gcd<_R1::den, _R2::den>::value;
static const intmax_t __n1 = _R1::num / __gcd_n1_n2;
static const intmax_t __d1 = _R1::den / __gcd_d1_d2;
static const intmax_t __n2 = _R2::num / __gcd_n1_n2;
static const intmax_t __d2 = _R2::den / __gcd_d1_d2;
static const intmax_t max = -((intmax_t(1) << (sizeof(intmax_t) * CHAR_BIT - 1)) + 1);
template <intmax_t _Xp, intmax_t _Yp, bool __overflow>
struct __mul // __overflow == false
{
static const intmax_t value = _Xp * _Yp;
};
template <intmax_t _Xp, intmax_t _Yp>
struct __mul<_Xp, _Yp, true>
{
static const intmax_t value = 1;
};
public:
static const bool value = (__n1 <= max / __d2) && (__n2 <= max / __d1);
typedef ratio<__mul<__n1, __d2, !value>::value,
__mul<__n2, __d1, !value>::value> type;
};
public:
typedef _Rep rep;
typedef _Period period;
@@ -440,9 +471,10 @@ public:
duration(const duration<_Rep2, _Period2>& __d,
typename enable_if
<
__no_overflow<_Period2, period>::value && (
treat_as_floating_point<rep>::value ||
(ratio_divide<_Period2, period>::type::den == 1 &&
!treat_as_floating_point<_Rep2>::value)
(__no_overflow<_Period2, period>::type::den == 1 &&
!treat_as_floating_point<_Rep2>::value))
>::type* = 0)
: __rep_(_VSTD::chrono::duration_cast<duration>(__d).count()) {}