Random double

[Ali Çehreli]

On 04/23/2013 07:43 AM, qznc wrote:

 > I want to generate a random "double" value, excluding wierdos like NaN
 > and Infinity. However, std.random.uniform seems to be useless. I tried
 > things like
 >
 >    std.random.uniform( double.min, double.max);
 >    std.random.uniform(-double.max, double.max);
 >    std.random.uniform(0.0, double.max);

Since double.max is a valid double value, you may want to call uniform 
with a closed range:

   uniform!"[]"(-double.max, double.max)

However, that still produces double.inf. :)

 > Should that be considered a bug?

I would say yes, it is a bug.

 > Nevertheless, any ideas how to work around that issue?

Floating point numbers have this interesting property where the number 
of representable values in the range [double.min_normal, 1) is equal to 
the number of representable values in the range [1, double.max]. The 
number line on this article should help with what I am trying to say:

   http://dlang.org/d-floating-point.html

So, to workaround this problem I would suggest simply using the 
following range:

         uniform(-1.0, 1.0);

One benefit is, now the range is open ended: You don't need to provide 
!"[)" to leave 1 out, because it is the default. On the other hand, the 
width of the range is now 2.0 so you must keep that in mind when you 
scale the value:

Additionally, note that the random numbers in the range between 
[-double.min_normal, double.min_normal] and outside of those may have a 
different distribution. Test before using. :) (I have no experience with 
floating point random numbers.)

Ali