Re: [boost] Re: Boost.MathConstants: Review

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-04-22 07:15:26

From: "Ed Brey" <brey_at_[hidden]>

> AFAICT, it is impossible to have a single interface that works for both:
>   (a) compile-time computation of expressions, and
>   (b) custom-binary values, which are more accurate than the compiler
> can produce.

Here's my take on this:

// Documented interface

namespace boost
{
    float const pi_f;
    double const pi;
    long double const pi_l;
}

// Possible implementation 1

namespace boost
{
    double const pi = 3.141592653...;
}

// Possible implementation 2

namespace boost
{
    extern double const pi;
}

// Possible implementation 3

namespace boost
{
    unsigned char const _pi[] = { insert suitably non-portable values
here };
    double const & pi = *(double*)_pi;
}

The user can hardly tell the difference between 1), 2) and 3).

For generic code, this may be supplemented with a numeric_limits-like
template, although I think that a static_cast<T>(pi_l) would probably
suffice.

--
Peter Dimov
Multi Media Ltd.