Ensure one of each

Co-authored-by: Matthew McPherrin <github@mcpherrin.ca>
Co-authored-by: Aaron Gable <aaron@aarongable.com>

Author: aarongable

ctpolicy/loglist/loglist.go

@@ -227,19 +227,19 @@ func (ll List) ForTime(expiry time.Time) List {
 }
 
 // Shuffle returns a new log list containing the exact same logs, but in a
-// nearly-randomly-shuffled order. If possible, it ensures that one of the first
-// two logs is a static-ct-api log, to boost the percentage of certs which
-// include an SCT from a static log.
+// nearly-randomly-shuffled order. If possible, it ensures that the first two
+// logs consist of one tiled log and one non-tiled log, to boost the percentage
+// of certs which include an SCT from a static log.
 func (ll List) Shuffle() List {
 	res := slices.Clone(ll)
 	rand.Shuffle(len(res), func(i int, j int) {
 		res[i], res[j] = res[j], res[i]
 	})
-	if len(res) > 2 && !res[0].Tiled && !res[1].Tiled {
-		// If we have more than two logs, and neither of the first two are tiled,
-		// try to bring a tiled log to the front of the list.
+	if len(res) > 2 && res[0].Tiled == res[1].Tiled {
+		// If we have more than two logs, and both are either tiled or not,
+		// try to bring another log to the front of the list.
 		for i := 2; i < len(res); i++ {
-			if res[i].Tiled {
+			if res[0].Tiled != res[i].Tiled {
 				res[0], res[i] = res[i], res[0]
 				break
 			}