1 files changed, 31 insertions, 8 deletions

diff --git a/src/pkg/time/zoneinfo.go b/src/pkg/time/zoneinfo.go
index 3c5774404..c44477f47 100644
--- a/src/pkg/time/zoneinfo.go
+++ b/src/pkg/time/zoneinfo.go
@@ -123,35 +123,58 @@ func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start
 	// Not using sort.Search to avoid dependencies.
 	tx := l.tx
 	end = 1<<63 - 1
-	for len(tx) > 1 {
-		m := len(tx) / 2
+	lo := 0
+	hi := len(tx)
+	for hi-lo > 1 {
+		m := lo + (hi-lo)/2
 		lim := tx[m].when
 		if sec < lim {
 			end = lim
-			tx = tx[0:m]
+			hi = m
 		} else {
-			tx = tx[m:]
+			lo = m
 		}
 	}
-	zone := &l.zone[tx[0].index]
+	zone := &l.zone[tx[lo].index]
 	name = zone.name
 	offset = zone.offset
 	isDST = zone.isDST
-	start = tx[0].when
+	start = tx[lo].when
 	// end = maintained during the search
 	return
 }
 
 // lookupName returns information about the time zone with
-// the given name (such as "EST").
-func (l *Location) lookupName(name string) (offset int, isDST bool, ok bool) {
+// the given name (such as "EST") at the given pseudo-Unix time
+// (what the given time of day would be in UTC).
+func (l *Location) lookupName(name string, unix int64) (offset int, isDST bool, ok bool) {
 	l = l.get()
+
+	// First try for a zone with the right name that was actually
+	// in effect at the given time. (In Sydney, Australia, both standard
+	// and daylight-savings time are abbreviated "EST". Using the
+	// offset helps us pick the right one for the given time.
+	// It's not perfect: during the backward transition we might pick
+	// either one.)
+	for i := range l.zone {
+		zone := &l.zone[i]
+		if zone.name == name {
+			nam, offset, isDST, _, _ := l.lookup(unix - int64(zone.offset))
+			if nam == zone.name {
+				return offset, isDST, true
+			}
+		}
+	}
+
+	// Otherwise fall back to an ordinary name match.
 	for i := range l.zone {
 		zone := &l.zone[i]
 		if zone.name == name {
 			return zone.offset, zone.isDST, true
 		}
 	}
+
+	// Otherwise, give up.
 	return
 }