Ticket #1479 (new todo)
Improve random-ness of Parrot_range_rand
|Reported by:||Austin_Hastings||Owned by:|
Parrot_range_rand(min, max, ignored) returns a number between min and max, inclusive. However, it does so by computing a floating point number, multiplying that be the integer difference, and adding it to the min. The result of this, in C, is that truncating conversion introduces a bias away from max. Consider a call Parrot_range_rand(0, 10, 0) - the result is min (0 in our case) plus (max-min) (10-0, or 10) times a random number in the range 0.0 ... 1.0. But because of truncating conversion, 10*(rand) will convert to 0 about 10% of the time (0.000 ... 0.099), 1 about 10% of the time (0.100 ... 0.199), ..., and 9 about 10% of the time (0.900 ... 0.999). About 0% of the time (there is a change of hitting 1.0, but floats have a lot of decimal places...) the result will be 10.