checkAndSet works now in any case

1 files changed, 20 insertions, 4 deletions

diff --git a/satp/sequence-window.go b/satp/sequence-window.go
index f529231..9fa4385 100644
--- a/satp/sequence-window.go
+++ b/satp/sequence-window.go
@@ -139,7 +139,23 @@ func (w *SequenceWindow) checkAndSet(sequenceNumber uint32) bool {
 }
 
 func (w *SequenceWindow) advanceTop(newTop uint32) {
-	// TODO: implement this
+	oldIdx := int(w.top() / 32)
+	newIdx := int(newTop / 32)
+	diff := newIdx - oldIdx
+	if oldIdx > newIdx {
+		diff = oldIdx - newIdx
+	}
+	oldHeadSlice := uint32(w.head)
+	w.head = uint64(newTop) << 32
+	for i := len(w.body) - 1; i >= 0; i-- {
+		if i < (diff - 1) {
+			w.body[i] = 0
+		} else if i < diff {
+			w.body[i] = oldHeadSlice
+		} else {
+			w.body[i] = w.body[i-diff]
+		}
+	}
 }
 
 func (w *SequenceWindow) top() uint32 {
@@ -182,10 +198,10 @@ func (w *SequenceWindow) CheckAndSet(sequenceNumber uint32) bool {
 	if lt && d > uint32(w.size) {
 		return false
 	}
-	if lt || top/32 == sequenceNumber/32 {
-		return w.checkAndSet(sequenceNumber)
+	if lt || top/32 == (sequenceNumber+1)/32 {
+		result := w.checkAndSet(sequenceNumber)
+		return result
 	}
-
 	// TODO: only now we would need the writers lock
 	w.advanceTop(sequenceNumber + 1)
 	return w.checkAndSet(sequenceNumber)