[boost] Re: Submission: Rational numbers

From: Andrew D Jewell (ajewell_at_[hidden])
Date: 1999-12-10 11:03:54

Back when I was writing rational number classes (in Ada of all 
things) I found that my integers would overflow with only the 
slightest provocation. The following changes would make the math less 
overflow prone, at the cost of some execution time.

in lcm, change
     return (n * m) / gcd(n, m);
to
     return (n * (m / gcd(n, m));

in += and -= change
         num = num * r.den + den * r.num;
         den *= r.den;
to
        newDen = lcm(den, r.den)
        num = num * (newDen / den) + r.num * (newDen / r.den)
        den = newDen;
        // it might be the case that the result is already normalised
        // in which case there is no extra cost.

I'm sure similar tricks could be used for *= and <, but I'm too lazy 
to figure them out again.

adj