[#91] Fixed the behavior of checkedAdd when over/underflow

stats.go

@@ -80,7 +80,10 @@ func checkedAdd(a, b int64) int64 {
 		return naiveSum
 	}
 	// we did over/under flow, if the sign is negative we should return math.MaxInt64 otherwise math.MinInt64.
-	return math.MaxInt64 + ((naiveSum >> 63) ^ 1)
+	if naiveSum < 0 {
+		return math.MaxInt64
+	}
+	return math.MinInt64
 }
 
 func negativeToMax(v int64) int64 {

stats_test.go

@@ -17,6 +17,7 @@ package otter
 import (
 	"math"
 	"testing"
+	"unsafe"
 )
 
 func TestStats(t *testing.T) {
@@ -59,3 +60,29 @@ func TestStats(t *testing.T) {
 		t.Fatalf("not valid evicted cost. want %d, got %d", expected, s.EvictedCost())
 	}
 }
+
+func TestCheckedAdd_Overflow(t *testing.T) {
+	if unsafe.Sizeof(t) != 8 {
+		t.Skip()
+	}
+
+	a := int64(math.MaxInt64)
+	b := int64(23)
+
+	if got := checkedAdd(a, b); got != math.MaxInt64 {
+		t.Fatalf("wrong overflow in checkedAdd. want %d, got %d", math.MaxInt64, got)
+	}
+}
+
+func TestCheckedAdd_Underflow(t *testing.T) {
+	if unsafe.Sizeof(t) != 8 {
+		t.Skip()
+	}
+
+	a := int64(math.MinInt64 + 10)
+	b := int64(-23)
+
+	if got := checkedAdd(a, b); got != math.MinInt64 {
+		t.Fatalf("wrong underflow in checkedAdd. want %d, got %d", math.MinInt64, got)
+	}
+}