time: use 1e9 rather than 1e-9 in Duration calculations

1e-9 has a 1 in the last place, causing some Duration calculations to
have unnecessary rounding errors.  1e9 does not, so use that instead.

Change-Id: I96334a2c47e7a014b532eb4b8a3ef9550e7ed057
Reviewed-on: https://go-review.googlesource.com/33116
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/time/time.go

@@ -603,21 +603,21 @@ func (d Duration) Nanoseconds() int64 { return int64(d) }
 func (d Duration) Seconds() float64 {
 	sec := d / Second
 	nsec := d % Second
-	return float64(sec) + float64(nsec)*1e-9
+	return float64(sec) + float64(nsec)/1e9
 }
 
 // Minutes returns the duration as a floating point number of minutes.
 func (d Duration) Minutes() float64 {
 	min := d / Minute
 	nsec := d % Minute
-	return float64(min) + float64(nsec)*(1e-9/60)
+	return float64(min) + float64(nsec)/(60*1e9)
 }
 
 // Hours returns the duration as a floating point number of hours.
 func (d Duration) Hours() float64 {
 	hour := d / Hour
 	nsec := d % Hour
-	return float64(hour) + float64(nsec)*(1e-9/60/60)
+	return float64(hour) + float64(nsec)/(60*60*1e9)
 }
 
 // Add returns the time t+d.

src/time/time_test.go

@@ -1003,6 +1003,21 @@ func TestDurationNanoseconds(t *testing.T) {
 	}
 }
 
+var secDurationTests = []struct {
+	d    Duration
+	want float64
+}{
+	{Duration(300000000), 0.3},
+}
+
+func TestDurationSeconds(t *testing.T) {
+	for _, tt := range secDurationTests {
+		if got := tt.d.Seconds(); got != tt.want {
+			t.Errorf("d.Seconds() = %g; want: %g", got, tt.want)
+		}
+	}
+}
+
 var minDurationTests = []struct {
 	d    Duration
 	want float64
@@ -1011,6 +1026,7 @@ var minDurationTests = []struct {
 	{Duration(-1), -1 / 60e9},
 	{Duration(1), 1 / 60e9},
 	{Duration(60000000000), 1},
+	{Duration(3000), 5e-8},
 }
 
 func TestDurationMinutes(t *testing.T) {
@@ -1029,6 +1045,7 @@ var hourDurationTests = []struct {
 	{Duration(-1), -1 / 3600e9},
 	{Duration(1), 1 / 3600e9},
 	{Duration(3600000000000), 1},
+	{Duration(36), 1e-11},
 }
 
 func TestDurationHours(t *testing.T) {