Scale the calculations in mon-pick by 2520.

The algorithm was designed with values based at 10000 in mind so numbers
small enough to zero off were not a concern, they could be avoided by scaling
up the data in other users of that code, but it's probably better to get rid
of gotchas rather than to document them.

1 files changed, 3 insertions, 1 deletions

diff --git a/crawl-ref/source/random-pick.h b/crawl-ref/source/random-pick.h
index 028f03c081..3ebdb3447e 100644
--- a/crawl-ref/source/random-pick.h
+++ b/crawl-ref/source/random-pick.h
@@ -60,7 +60,9 @@ T random_picker<T, max>::pick(const random_pick_entry<T> *weights, int level,
         if (veto(pop->value))
             continue;
 
-        int rar = rarity_at(pop, level);
+        // 2520 is divisible by any number 1..10, and provides enough scale
+        // to make round-off errors even for degenerate distributions ok.
+        int rar = rarity_at(pop, level) * 2520;
         ASSERTM(rar > 0, "Rarity %d: %d at level %d", rar, pop->value, level);
 
         valid[nvalid].value = pop->value;