Test the quality of the random generator by using a histogram to visualise the distribution.
The quality of the built-in generator of random numbers fully depends on the algorithm the developers of the compiler used. As a user, you cannot do much to change the existing generator, but you can always test if it delivers numbers uniformly distributed across the whole interval.
In Perl 6, there is the
rand routine (see Task 32, Generating random numbers) that returns a floating-point number (actually, the value of the
Num type) between 0 and 1. We will run it 100,000 times, filling the histogram containing 10 cells. Each random number falls into one of them. For example, the numbers between 0 and 0.1 land in the first cell, the numbers between 0.1 and 0.2 in the second, and so on.
@histogram[10 * rand]++ for 1..100_000;
Examine the way the index for the
@histogram array is formed. A random integer between 0 and 1 is first multiplied by 10 and then an integer part of it is taken because the array indexing operator
[ ] needs integers only. It is also possible to do the conversion explicitly:
@histogram[(10 * rand).Int]++
Run the program a few times. Here’s the output of a couple of runs of the program, and it printed more or less equal numbers in each cell:
[10062 9818 10057 9922 10002 10118 9978 9959 10013 10071]
[9959 9957 9813 9933 10160 10030 10036 10032 10059 10021]