[varStore] Micro-optimize storeDeltas()

Also speed up the test slightly by skipping rounding.

Lib/fontTools/varLib/varStore.py

@@ -95,6 +95,7 @@ class OnlineVarStoreBuilder(object):
         return base, self.storeDeltas(deltas, round=noRound)
 
     def storeDeltas(self, deltas, *, round=round):
+        if round != noRound:
             deltas = [round(d) for d in deltas]
         if len(deltas) == len(self._supports) + 1:
             deltas = tuple(deltas[1:])
@@ -121,6 +122,7 @@ class OnlineVarStoreBuilder(object):
 
 
 def VarData_addItem(self, deltas, *, round=round):
+    if round != noRound:
         deltas = [round(d) for d in deltas]
 
     countUs = self.VarRegionCount

Tests/varLib/varStore_test.py

@@ -1,6 +1,7 @@
 import pytest
 from io import StringIO
 from fontTools.misc.xmlWriter import XMLWriter
+from fontTools.misc.roundTools import noRound
 from fontTools.varLib.models import VariationModel
 from fontTools.varLib.varStore import OnlineVarStoreBuilder, VarStoreInstancer
 from fontTools.ttLib import TTFont, newTable
@@ -269,7 +270,7 @@ def test_optimize_overflow():
 
     for data in range(0, 0xFFFF * 2):
         data = [0, data]
-        builder.storeMasters(data)
+        builder.storeMasters(data, round=noRound)
 
     varStore = builder.finish()
     varStore.optimize()