rn2

rn2(x)
Probability mass function of rn2(10).
Distribution	uniform
Mean	$(x-1)/2$
Standard deviation	$\sqrt{(x^2-1)/12}$

rn2(x) is a pseudo-random number function used in NetHack when a result should be unweighted. The range of values is between 0 and x-1 inclusive (that is, 0 ≤ rn2(x) < x).

For example, to simulate a percentage chance:

if (rn2(100) < chance) { ... }

Also,

!rn2(x)

is true with a 1/x probability.

See also rn1.