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Diffstat (limited to 'libgo/go/time/zoneinfo.go')
-rw-r--r-- | libgo/go/time/zoneinfo.go | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/libgo/go/time/zoneinfo.go b/libgo/go/time/zoneinfo.go new file mode 100644 index 0000000..aca56e7 --- /dev/null +++ b/libgo/go/time/zoneinfo.go @@ -0,0 +1,191 @@ +// Copyright 2011 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package time + +import "sync" + +// A Location maps time instants to the zone in use at that time. +// Typically, the Location represents the collection of time offsets +// in use in a geographical area, such as CEST and CET for central Europe. +type Location struct { + name string + zone []zone + tx []zoneTrans + + // Most lookups will be for the current time. + // To avoid the binary search through tx, keep a + // static one-element cache that gives the correct + // zone for the time when the Location was created. + // if cacheStart <= t <= cacheEnd, + // lookup can return cacheZone. + // The units for cacheStart and cacheEnd are seconds + // since January 1, 1970 UTC, to match the argument + // to lookup. + cacheStart int64 + cacheEnd int64 + cacheZone *zone +} + +// A zone represents a single time zone such as CEST or CET. +type zone struct { + name string // abbreviated name, "CET" + offset int // seconds east of UTC + isDST bool // is this zone Daylight Savings Time? +} + +// A zoneTrans represents a single time zone transition. +type zoneTrans struct { + when int64 // transition time, in seconds since 1970 GMT + index uint8 // the index of the zone that goes into effect at that time + isstd, isutc bool // ignored - no idea what these mean +} + +// UTC represents Universal Coordinated Time (UTC). +var UTC *Location = &utcLoc + +// utcLoc is separate so that get can refer to &utcLoc +// and ensure that it never returns a nil *Location, +// even if a badly behaved client has changed UTC. +var utcLoc = Location{name: "UTC"} + +// Local represents the system's local time zone. +var Local *Location = &localLoc + +// localLoc is separate so that initLocal can initialize +// it even if a client has changed Local. +var localLoc Location +var localOnce sync.Once + +func (l *Location) get() *Location { + if l == nil { + return &utcLoc + } + if l == &localLoc { + localOnce.Do(initLocal) + } + return l +} + +// String returns a descriptive name for the time zone information, +// corresponding to the argument to LoadLocation. +func (l *Location) String() string { + return l.get().name +} + +// FixedZone returns a Location that always uses +// the given zone name and offset (seconds east of UTC). +func FixedZone(name string, offset int) *Location { + l := &Location{ + name: name, + zone: []zone{{name, offset, false}}, + tx: []zoneTrans{{-1 << 63, 0, false, false}}, + cacheStart: -1 << 63, + cacheEnd: 1<<63 - 1, + } + l.cacheZone = &l.zone[0] + return l +} + +// lookup returns information about the time zone in use at an +// instant in time expressed as seconds since January 1, 1970 00:00:00 UTC. +// +// The returned information gives the name of the zone (such as "CET"), +// the start and end times bracketing sec when that zone is in effect, +// the offset in seconds east of UTC (such as -5*60*60), and whether +// the daylight savings is being observed at that time. +func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start, end int64) { + l = l.get() + + if len(l.tx) == 0 { + name = "UTC" + offset = 0 + isDST = false + start = -1 << 63 + end = 1<<63 - 1 + return + } + + if zone := l.cacheZone; zone != nil && l.cacheStart <= sec && sec < l.cacheEnd { + name = zone.name + offset = zone.offset + isDST = zone.isDST + start = l.cacheStart + end = l.cacheEnd + return + } + + // Binary search for entry with largest time <= sec. + // Not using sort.Search to avoid dependencies. + tx := l.tx + end = 1<<63 - 1 + for len(tx) > 1 { + m := len(tx) / 2 + lim := tx[m].when + if sec < lim { + end = lim + tx = tx[0:m] + } else { + tx = tx[m:] + } + } + zone := &l.zone[tx[0].index] + name = zone.name + offset = zone.offset + isDST = zone.isDST + start = tx[0].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) { + l = l.get() + for i := range l.zone { + zone := &l.zone[i] + if zone.name == name { + return zone.offset, zone.isDST, true + } + } + return +} + +// lookupOffset returns information about the time zone with +// the given offset (such as -5*60*60). +func (l *Location) lookupOffset(offset int) (name string, isDST bool, ok bool) { + l = l.get() + for i := range l.zone { + zone := &l.zone[i] + if zone.offset == offset { + return zone.name, zone.isDST, true + } + } + return +} + +// NOTE(rsc): Eventually we will need to accept the POSIX TZ environment +// syntax too, but I don't feel like implementing it today. + +// NOTE(rsc): Using the IANA names below means ensuring we have access +// to the database. Probably we will ship the files in $GOROOT/lib/zoneinfo/ +// and only look there if there are no system files available (such as on Windows). +// The files total 200 kB. + +// LoadLocation returns the Location with the given name. +// +// If the name is "" or "UTC", LoadLocation returns UTC. +// If the name is "Local", LoadLocation returns Local. +// +// Otherwise, the name is taken to be a location name corresponding to a file +// in the IANA Time Zone database, such as "America/New_York". +func LoadLocation(name string) (*Location, error) { + if name == "" || name == "UTC" { + return UTC, nil + } + if name == "Local" { + return Local, nil + } + return loadLocation(name) +} |