ee7502ac
by Sergio Gelato
at 2020-06-22T17:27:30+00:00
ITS#8204 Remove bias towards the first record in RFC2782 shuffle implementation.
Prior to this change, given two records of weight 1 the algorithm would
return them in the order (0,1) with 100% probability instead of the
desired 50%. This was due to an off-by-one error in the range test.
srv_rand() returns a float in the range [0.0, 1.0[, so r is an integer in the
range [0, total[. The correct probability for record 0 to be chosen is
a[0].weight/total, not (a[0].weight+1)/total.
8006ee58
by Sergio Gelato
at 2020-06-22T17:27:30+00:00
ITS#8204 Improved RFC2782 shuffle when several, but not all, records have weight 0.
The fallback to a straight Fisher-Yates shuffle needs to occur whenever the
sum of the *remaining* weights is zero, or else the remaining records will
not be reordered. Testing only once at the beginning covers the case when
all weights are zero, and obviously no shuffling is needed when only one
weight is zero; but other weight combinations are possible, such as (1, 0, 0).