
Boost : 
From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 20040229 06:52:09
Dear boosters,
I discovered something that at least was new to me. It's a simple way of
coding floating point
constants s.t.
1. no overhead at all
2. no order dependencies occur
3. the context in which the constant appears decides the precision of the
constants [important in template code]
4. whenever a narrowing or widening conversion is required, explicit action
must be taken by the programmer to determine what he wants
5. all precisions of the constants coexist, so there is no need for several
headers
Example:
#include "math_constant.hpp"
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
template< typename T >
void test();
int main()
{
cout << setprecision( 10 );
test<float>();
test<double>();
test<long double>();
// cout << pi; // ambiguous
cout << float( pi ) << " " << double( pi ) << " " << (long double)(
pi ); // ok
// int i = pi; // ambiguous
int i = float( pi ); // ok
cout << sqrt( float( pi ) );
}
template< typename T >
void test()
{
T two_pi = T(2) * pi;
two_pi = T(pi) + pi; // note: pi operator X() pi is ambiguous
T plus = T(1) + pi;
T minus = pi  T(1);
T divide = pi / T(2);
T all = pi + T(3)  T(pi) * pi / T(3); // also ambiguous
cout << T( pi ) << " ";
}
Any comments are more than welcome. I know there are several proposals for
defining math constants,
but I don't see what the big problems are (so please help me understand them
:) )
br
Thorsten
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