Demonstrate error rate of reduced-precision HLLs
diff --git a/test/hyper_test.erl b/test/hyper_test.erl
index e6d4032..94590e7 100644
--- a/test/hyper_test.erl
+++ b/test/hyper_test.erl
@@ -59,12 +59,21 @@
reduce_precision_t() ->
- [?assertEqual(1, trunc(
- hyper:card(
- hyper:reduce_precision(4,
- hyper:insert(<<"1">>, hyper:new(6, Mod))))))
- %|| Mod <- backends()].
- || Mod <- [hyper_binary]].
+ random:seed(1, 2, 3),
+ Card = 1000,
+ Values = generate_unique(Card),
+ [begin
+ HighRes = hyper:insert_many(Values, hyper:new(16, Mod)),
+ lists:foreach(
+ fun (P) ->
+ Estimate = hyper:card(hyper:reduce_precision(P, HighRes)),
+ % accept error rate for one precision step less
+ M = trunc(math:pow(2, P-1)),
+ Error = 1.04 / math:sqrt(M),
+ ?assert(abs(Estimate - Card) < Card * Error)
+ end, lists:seq(4, 15))
+ %end || Mod <- backend()].
+ end || Mod <- [hyper_binary]].
backend_t() ->
