lib/std: better policy for enlarging HashCollection

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/collection/hash_collection.nit b/lib/standard/collection/hash_collection.nit
index c2c8353..2def742 100644 (file)
--- a/lib/standard/collection/hash_collection.nit
+++ b/lib/standard/collection/hash_collection.nit
@@ -91,9 +91,13 @@ private abstract class HashCollection[K: Object, N: HashNode[Object]]
                # Enlarge if needed
                var l = _length
                _length = l + 1
-               l = (l + 5) * 3 / 2
+
+               # Magic values determined empirically
+               # We do not want to enlarge too much
+               # We also want a odd capacity so that the modulo is more distributive
+               l = (l + 5) * 2 + 1
                if l >= _capacity then
-                       enlarge(l * 2)
+                       enlarge(l * 3 / 2 + 1)
                end
        end