test: add test of NaN in map

R=iant, r
CC=golang-dev
https://golang.org/cl/5576071

test/map.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"math"
 	"strconv"
+	"time"
 )
 
 const count = 100
@@ -27,6 +28,12 @@ func P(a []string) string {
 }
 
 func main() {
+	testbasic()
+	testfloat()
+	testnan()
+}
+
+func testbasic() {
 	// Test a map literal.
 	mlit := map[string]int{"0": 0, "1": 1, "2": 2, "3": 3, "4": 4}
 	for i := 0; i < len(mlit); i++ {
@@ -489,8 +496,6 @@ func main() {
 	for _, _ = range mnil {
 		panic("range mnil")
 	}
-
-	testfloat()
 }
 
 func testfloat() {
@@ -646,3 +651,26 @@ func testfloat() {
 		}
 	}
 }
+
+func testnan() {
+	// Test that NaNs in maps don't go quadratic.
+	t := func(n int) time.Duration {
+		t0 := time.Now()
+		m := map[float64]int{}
+		nan := math.NaN()
+		for i := 0; i < n; i++ {
+			m[nan] = 1
+		}
+		if len(m) != n {
+			panic("wrong size map after nan insertion")
+		}
+		return time.Since(t0)
+	}
+
+	n := 30000 // 0.02 seconds on a MacBook Air
+	t1 := t(n)
+	t2 := t(2 * n)
+	if t2 > 3*t1 { // should be 2x (linear); allow up to 3x
+		fmt.Printf("too slow: %d inserts: %v; %d inserts: %v\n", n, t1, 2*n, t2)
+	}
+}