time: another bug in SecondsToUTC.

added random test to look for more.

Fixes #363.

R=r, cw
https://golang.org/cl/163071

diff --git a/src/pkg/time/time.go b/src/pkg/time/time.go
index 9a767b458e0268d3d8ec21fa930456ad155951d5..1418d521e60b108344642002e1a1028156d71944 100644 (file)
--- a/src/pkg/time/time.go
+++ b/src/pkg/time/time.go
@@ -113,16 +113,25 @@ func SecondsToUTC(sec int64) *Time {
 
        // Cut off 100-year cycles
        n = day / daysPer100Years;
+       if n > 3 {      // happens on last day of 400th year
+               n = 3
+       }
        year += 100 * n;
        day -= daysPer100Years * n;
 
        // Cut off 4-year cycles
        n = day / daysPer4Years;
+       if n > 24 {     // happens on last day of 100th year
+               n = 24
+       }
        year += 4 * n;
        day -= daysPer4Years * n;
 
        // Cut off non-leap years.
        n = day / 365;
+       if n > 3 {      // happens on last day of 4th year
+               n = 3
+       }
        year += n;
        day -= 365 * n;
 

diff --git a/src/pkg/time/time_test.go b/src/pkg/time/time_test.go
index da1c7cbf365caf666187d6c671744c9d73601f1e..88b16ee26a4e791cde9d2e194b56cd55b637a88e 100644 (file)
--- a/src/pkg/time/time_test.go
+++ b/src/pkg/time/time_test.go
@@ -7,6 +7,7 @@ package time_test
 import (
        "os";
        "testing";
+       "testing/quick";
        . "time";
 )
 
@@ -27,6 +28,8 @@ var utctests = []TimeTest{
        TimeTest{1221681866, Time{2008, 9, 17, 20, 4, 26, Wednesday, 0, "UTC"}},
        TimeTest{-1221681866, Time{1931, 4, 16, 3, 55, 34, Thursday, 0, "UTC"}},
        TimeTest{-11644473600, Time{1601, 1, 1, 0, 0, 0, Monday, 0, "UTC"}},
+       TimeTest{599529660, Time{1988, 12, 31, 0, 1, 0, Saturday, 0, "UTC"}},
+       TimeTest{978220860, Time{2000, 12, 31, 0, 1, 0, Sunday, 0, "UTC"}},
        TimeTest{1e18, Time{31688740476, 10, 23, 1, 46, 40, Friday, 0, "UTC"}},
        TimeTest{-1e18, Time{-31688736537, 3, 10, 22, 13, 20, Tuesday, 0, "UTC"}},
        TimeTest{0x7fffffffffffffff, Time{292277026596, 12, 4, 15, 30, 7, Sunday, 0, "UTC"}},
@@ -84,6 +87,20 @@ func TestSecondsToLocalTime(t *testing.T) {
        }
 }
 
+func TestSecondsToUTCAndBack(t *testing.T) {
+       f := func(sec int64) bool { return SecondsToUTC(sec).Seconds() == sec };
+       f32 := func(sec int32) bool { return f(int64(sec)) };
+       cfg := &quick.Config{MaxCount: 10000};
+
+       // Try a reasonable date first, then the huge ones.
+       if err := quick.Check(f32, cfg); err != nil {
+               t.Fatal(err)
+       }
+       if err := quick.Check(f, cfg); err != nil {
+               t.Fatal(err)
+       }
+}
+
 func BenchmarkSeconds(b *testing.B) {
        for i := 0; i < b.N; i++ {
                Seconds()