time: restore support for large negative days in Date

CL 586257 converted days to uint32 which is usually fine but fails for
negative days close to cycle boundaries.

Fixes #68718

Change-Id: I8dc5b8fe0c7c1921beb204da1913b9a1ab39280d
Reviewed-on: https://go-review.googlesource.com/c/go/+/602815
Reviewed-by: Rob Pike <r@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/time/time.go b/src/time/time.go
index 54c4bfdba35f181689d49c790ff01692411deaa4..572ea64ccfcd88efa2c4f6e0432bc8952f5e4f45 100644 (file)
--- a/src/time/time.go
+++ b/src/time/time.go
@@ -591,6 +591,7 @@ type absJanFeb int
 
 // dateToAbsDays takes a standard year/month/day and returns the
 // number of days from the absolute epoch to that day.
+// The days argument can be out of range and in particular can be negative.
 func dateToAbsDays(year int64, month Month, day int) absDays {
        // See “Computations on Times” comment above.
        amonth := uint32(month)
@@ -626,7 +627,7 @@ func dateToAbsDays(year int64, month Month, day int) absDays {
        cday := 1461 * cyear / 4
        centurydays := 146097 * century / 4
 
-       return absDays(centurydays + uint64(cday+ayday+uint32(day)-1))
+       return absDays(centurydays + uint64(int64(cday+ayday)+int64(day)-1))
 }
 
 // days converts absolute seconds to absolute days.

diff --git a/src/time/time_test.go b/src/time/time_test.go
index bd2c01649fb46168b9cd3f907dbc9aa78d23c77d..e375d3f97340cbe1e5deb9fa10bad2f579251d6d 100644 (file)
--- a/src/time/time_test.go
+++ b/src/time/time_test.go
@@ -666,6 +666,9 @@ var dateTests = []struct {
        {2012, 1, -43, 7, 56, 35, 0, Local, 1321631795},                 // Jan -52 7:56:35 2012
        {2012, int(January - 2), 18, 7, 56, 35, 0, Local, 1321631795},   // (Jan-2) 18 7:56:35 2012
        {2010, int(December + 11), 18, 7, 56, 35, 0, Local, 1321631795}, // (Dec+11) 18 7:56:35 2010
+       {1970, 1, 15297, 7, 56, 35, 0, Local, 1321631795},               // large number of days
+
+       {1970, 1, -25508, 0, 0, 0, 0, Local, -2203948800}, // negative Unix time
 }
 
 func TestDate(t *testing.T) {
@@ -704,6 +707,13 @@ func TestAddDate(t *testing.T) {
                                time, t1)
                }
        }
+
+       t2 := Date(1899, 12, 31, 0, 0, 0, 0, UTC)
+       days := t2.Unix() / (24 * 60 * 60)
+       t3 := Unix(0, 0).AddDate(0, 0, int(days))
+       if !t2.Equal(t3) {
+               t.Errorf("Adddate(0, 0, %d) = %v, want %v", days, t3, t2)
+       }
 }
 
 var daysInTests = []struct {