[Random] bug in uniform_int or uniform_smallint

From: Douglas Gregor (gregod_at_[hidden])
Date: 2002-03-07 16:51:24

This code in uniform_int:
 120     if(_brange / _range > 4 /* quantization_cutoff */ ) {
 121       // the new range is vastly smaller than the source range,
 122       // so quantization effects are not relevant
 123       return uniform_smallint<base_type,result_type>(_rng, _min, _max)();
 124     } else {

will make uniform_smallint do very bad things when _max-_min+1 is large 
enough to make 32*_range*_range (where _range = _max-_min+1 at line 95 of 
uniform_smallint.hpp) overflow and become negative. Then we get stuck in the 
following loop forever (uniform_smallint.hpp):

  95     const base_result r = 32*_range*_range;
  96     for(; r_base >= r; _factor *= 2)
  97       r_base /= 2;

I don't know enough about this to know if uniform_int should take care of 
this (and not deflect to uniform_smallint if it would overflow), or if 
uniform_smallint should deal with this overflow itself.

        Doug