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Compute greatest common divisor to prevent unnecessary integer overflow.

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Fixes boost trac tickets #9662, #9778.
This commit is contained in:
Christopher Kohlhoff 2014-04-29 22:31:47 +10:00
parent d8240be4df
commit 3b2335010d
1 changed files with 15 additions and 2 deletions
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17
asio/include/asio/detail/chrono_time_traits.hpp
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@ -22,6 +22,13 @@
namespace asio {
namespace detail {
// Helper template to compute the greatest common divisor.
template <int64_t v1, int64_t v2>
struct gcd { enum { value = gcd<v2, v1 % v2>::value }; };
template <int64_t v1>
struct gcd<v1, 0> { enum { value = v1 }; };
// Adapts std::chrono clocks for use with a deadline timer.
template <typename Clock, typename WaitTraits>
struct chrono_time_traits
@ -146,8 +153,14 @@ struct chrono_time_traits
template <int64_t Num, int64_t Den>
int64_t duration_cast() const
{
const int64_t num = period_type::num * Den;
const int64_t den = period_type::den * Num;
const int64_t num1 = period_type::num / gcd<period_type::num, Num>::value;
const int64_t num2 = Num / gcd<period_type::num, Num>::value;
const int64_t den1 = period_type::den / gcd<period_type::den, Den>::value;
const int64_t den2 = Den / gcd<period_type::den, Den>::value;
const int64_t num = num1 * den2;
const int64_t den = num2 * den1;
if (num == 1 && den == 1)
return ticks();