core: latticeData supports config change (#190)

* Add test for num of chains changes.
* Return error in latticeData.prepareBlock
* Compare two positions
* Modify chainStatus from height-based to index-based.
* Fix consensus to use round variable
* Remove sanity check in chainStatus
* Fixup: refine sanity check
 - verify if round switching is required or not by
   chainTip's config.
 - make the logic in sanity check more clear
 - pospone acking relationship checking, they
   are more expensive to check.

1 files changed, 8 insertions, 0 deletions

diff --git a/core/utils.go b/core/utils.go
index 3c1d211..ac95678 100644
--- a/core/utils.go
+++ b/core/utils.go
@@ -130,3 +130,11 @@ func HashConfigurationBlock(
 		prevHash[:],
 	)
 }
+
+// DiffUint64 calculates difference between two uint64.
+func DiffUint64(a, b uint64) uint64 {
+	if a > b {
+		return a - b
+	}
+	return b - a
+}