prog: fix corner case in normalizePrio

Based on twitter bug report:
https://twitter.com/panicaII/status/1035058001269248000

2 files changed, 31 insertions, 0 deletions

diff --git a/prog/prio.go b/prog/prio.go
index 0e726f702..95713392e 100644
--- a/prog/prio.go
+++ b/prog/prio.go
@@ -175,6 +175,9 @@ func normalizePrio(prios [][]float32) {
 		if nzero != 0 {
 			min /= 2 * float32(nzero)
 		}
+		if min == max {
+			max = 0
+		}
 		for i, p := range prio {
 			if max == 0 {
 				prio[i] = 1
diff --git a/prog/prio_test.go b/prog/prio_test.go
new file mode 100644
index 000000000..06a72f75b
--- /dev/null
+++ b/prog/prio_test.go
@@ -0,0 +1,28 @@
+// Copyright 2018 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package prog
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestNormalizePrio(t *testing.T) {
+	prios := [][]float32{
+		{2, 2, 2},
+		{1, 2, 4},
+		{1, 2, 0},
+	}
+	want := [][]float32{
+		{1, 1, 1},
+		{0.1, 0.4, 1},
+		{0.4, 1, 0.1},
+	}
+	t.Logf("had:  %+v", prios)
+	normalizePrio(prios)
+	if !reflect.DeepEqual(prios, want) {
+		t.Logf("got:  %+v", prios)
+		t.Errorf("want: %+v", want)
+	}
+}