Re: [boost] [multiprecision] Bug in double to cpp_bin_float conversion?

Subject: Re: [boost] [multiprecision] Bug in double to cpp_bin_float conversion?
From: Peter Dimov (lists_at_[hidden])
Date: 2016-04-13 17:44:13

Rob Conde wrote:
> Consider the following code:
>
> #include <boost/multiprecision/cpp_bin_float.hpp>
> #include <iostream>
>
> int main()
> {
>     typedef boost::multiprecision::cpp_bin_float_quad float128_t;
>
>     float128_t f1(1e-9);
>     float128_t f2("1e-9");
>
>     std::cout << 
> std::setprecision(std::numeric_limits<float128_t>::max_digits10);
>
>     std::cout << f1 << std::endl;
>     std::cout << f2 << std::endl;
>
>     return 0;
> }
>
> I'm getting as output:
>
> 1.000000000000000062281591457779856419e-09
> 9.999999999999999999999999999999999325e-10
>
> The conversion of the double literal is not as expected.
>
> On wand box: http://melpon.org/wandbox/permlink/uSGNQZAEEytmb3ao
>
> Is this a bug? If not, what would be the correct way to get my expected 
> behavior?

What behavior do you expect?