From 17b31925feb6e14159c9583f4ac9d26c01f3e16c Mon Sep 17 00:00:00 2001
From: Trevor Pounds <trevor.pounds@gmail.com>
Date: Thu, 23 Apr 2015 09:23:33 -0700
Subject: [PATCH] Prevent negative hashcodes for all set operations.

---
 helper/schema/set.go      | 18 ++++++++++++------
 helper/schema/set_test.go |  4 ++++
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/helper/schema/set.go b/helper/schema/set.go
index a10c2b8d95..fbfd789874 100644
--- a/helper/schema/set.go
+++ b/helper/schema/set.go
@@ -34,7 +34,7 @@ func (s *Set) Add(item interface{}) {
 
 // Contains checks if the set has the given item.
 func (s *Set) Contains(item interface{}) bool {
-	_, ok := s.m[s.F(item)]
+	_, ok := s.m[s.hash(item)]
 	return ok
 }
 
@@ -122,10 +122,7 @@ func (s *Set) init() {
 func (s *Set) add(item interface{}) int {
 	s.once.Do(s.init)
 
-	code := s.F(item)
-	if code < 0 {
-		code *= -1
-	}
+	code := s.hash(item)
 	if _, ok := s.m[code]; !ok {
 		s.m[code] = item
 	}
@@ -133,8 +130,17 @@ func (s *Set) add(item interface{}) int {
 	return code
 }
 
+func (s *Set) hash(item interface{}) int {
+	code := s.F(item)
+	// Always return a nonnegative hashcode.
+	if code < 0 {
+		return -code
+	}
+	return code
+}
+
 func (s *Set) index(item interface{}) int {
-	return sort.SearchInts(s.listCode(), s.F(item))
+	return sort.SearchInts(s.listCode(), s.hash(item))
 }
 
 func (s *Set) listCode() []int {
diff --git a/helper/schema/set_test.go b/helper/schema/set_test.go
index 9688c5f715..8717735550 100644
--- a/helper/schema/set_test.go
+++ b/helper/schema/set_test.go
@@ -35,6 +35,7 @@ func TestSetAdd_negative(t *testing.T) {
 func TestSetContains(t *testing.T) {
 	s := &Set{F: testSetInt}
 	s.Add(5)
+	s.Add(-5)
 
 	if s.Contains(2) {
 		t.Fatal("should not contain")
@@ -42,6 +43,9 @@ func TestSetContains(t *testing.T) {
 	if !s.Contains(5) {
 		t.Fatal("should contain")
 	}
+	if !s.Contains(-5) {
+		t.Fatal("should contain")
+	}
 }
 
 func TestSetDifference(t *testing.T) {