Using rand() % 3, the number 0 would be twice as likely to appear.
With a very large RNG range, the effect becomes less prevalent but
still present. This can be solved by modifying the range of the RNG
- to become a multiple of bound by dropping values above the a threshhold.
- In our example, threshhold == 4 - 3 = 1 % 3 == 1, so reject 0, thus
+ to become a multiple of bound by dropping values above the a threshold.
+ In our example, threshold == 4 - 3 = 1 % 3 == 1, so reject 0, thus
making the range 3 with no bias.
This loop looks dangerous, but will always terminate due to the
RNG's property of uniformity.
*/
- u32 threshhold = -bound % bound;
+ u32 threshold = -bound % bound;
u32 r;
- while ((r = next()) < threshhold)
+ while ((r = next()) < threshold)
;
return r % bound;