

DIRECTORY
BasicTime USING [DayOfWeek, ExtendedGMT, minutesPerHour, MonthOfYear, nullGMT, Pulses, secondsPerMinute, Unpacked, UnpackedPeriod, unspecifiedTP, unspecifiedZone, Zone, ZoneAndDST],
BasicTimeBackdoor,
HostTime USING [ExtendedGMTFromHostTime, GetTime, GetZoneAndDST, TimeToMicroseconds];

BasicTimeImpl: CEDAR MONITOR
IMPORTS HostTime
EXPORTS BasicTime, BasicTimeBackdoor
= { OPEN BasicTime;
knownTP: ZoneAndDST;
knownTPValid: BOOL м FALSE;
OutOfRange: PUBLIC ERROR = CODE;

TimeNotKnown: PUBLIC ERROR = CODE;

TimeParametersNotKnown: PUBLIC ERROR = CODE;

GetClockPulses: PUBLIC PROC RETURNS [CARD] = TRUSTED {
RETURN[HostTime.TimeToMicroseconds[HostTime.GetTime[]]]
};

PulsesToMicroseconds: PUBLIC PROC [p: Pulses] RETURNS [CARD] = {
RETURN [p];
};

PulsesToSeconds: PUBLIC PROC [p: Pulses] RETURNS [s: REAL] = {
RETURN [p*1.0e-6];
};

MicrosecondsToPulses: PUBLIC PROC [m: CARD] RETURNS [Pulses] = {
RETURN [m];
};

GMT: PUBLIC TYPE = INT;

gmtBaseYear: CARDINAL = 1968;

gmtOrigin: GMT = 0; -- representation for midnight, January 1st 1968 GMT

alto1968: CARD = -- our time origin in Alto/Pup format --
LONG[ (gmtBaseYear-1901) * 365 + (gmtBaseYear-1901)/4 ] * 24 * 60 * 60;

altoExpiry: CARD = LAST[CARD] - alto1968;

gmtExpiry: INT = -- intersection of Alto expiry and 31 bits, minus "nullGMT" representation --
CARD[gmtOrigin] + 
(IF altoExpiry > CARD[LAST[INT]] THEN LAST[INT] - gmtOrigin - 1 
ELSE MIN[altoExpiry, CARD[LAST[INT]] - CARD[gmtOrigin] - 1]) 
- 1;

earliestGMT: PUBLIC GMT м gmtOrigin + LONG[LAST[Zone]] * 60;

latestGMT: PUBLIC GMT м gmtExpiry;

nullGMT: GMT ~ BasicTime.nullGMT;


Now: PUBLIC PROC RETURNS [gmt: GMT] = TRUSTED {
gmt м HostTime.ExtendedGMTFromHostTime[HostTime.GetTime[]].gmt;
};

ExtendedNow: PUBLIC PROC RETURNS [egmt: ExtendedGMT] = TRUSTED {
egmt м HostTime.ExtendedGMTFromHostTime[HostTime.GetTime[]];
};

Period: PUBLIC PROC [from, to: GMT] RETURNS [INT] = {
RETURN [to-from];
};

Update: PUBLIC PROC [base: GMT, period: INT] RETURNS [GMT] = {
IF period IN [gmtOrigin-base .. gmtExpiry-base]
THEN RETURN [base+period]
ELSE ERROR OutOfRange;
};

ToPupTime: PUBLIC PROC [g: GMT] RETURNS [ CARD ] = {
RETURN [alto1968+CARD[g-gmtOrigin]];
};

ToNSTime: PUBLIC PROC [g: GMT] RETURNS [ CARD ] = {
RETURN [alto1968+CARD[g-gmtOrigin]];
};

FromPupTime: PUBLIC PROC [p: CARD] RETURNS [ GMT ] = {
IF p >= alto1968 THEN RETURN [(p-alto1968)+gmtOrigin] ELSE ERROR OutOfRange;
};

FromNSTime: PUBLIC PROC [p: CARD] RETURNS [ GMT ] = {
IF p >= alto1968 THEN RETURN [(p-alto1968)+gmtOrigin] ELSE ERROR OutOfRange;
};


monthTable: ARRAY MonthOfYear OF CARDINAL =
[0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366];

startWeekday: DayOfWeek = Monday; -- January 1st 1968 was a Monday

UnpackZ: PUBLIC PROC [time: GMT, tp: ZoneAndDST] RETURNS [ unpacked: Unpacked ] = {
secs, mins, hrs: CARD;
IF time < earliestGMT OR time > latestGMT THEN ERROR OutOfRange[];
secs м time - gmtOrigin;
mins м secs / 60 -
(IF tp.zone = unspecifiedZone THEN 0 ELSE tp.zone);
hrs м mins / 60;
unpacked.second м secs MOD 60;
unpacked.minute м mins MOD 60;
unpacked.zone м (IF tp.zone = unspecifiedZone THEN 0 ELSE tp.zone);
unpacked.dst м no;
DO -- once if not dst, twice if dst
daysSinceBase: CARDINAL = hrs / 24;
daysInFourYears: CARDINAL = ( 3*365 + 366 );
fourYears: CARDINAL = daysSinceBase / daysInFourYears;
daysBeyondFourYears: CARDINAL = daysSinceBase MOD daysInFourYears;
pseudoDaysBeyond: CARDINAL = -- corrected as if every year had 366 days
daysBeyondFourYears + (MAX[31+29,daysBeyondFourYears]-(31+29))/365;
oddYears: [0..4) = pseudoDaysBeyond / 366;
dayOfYear: CARDINAL = (pseudoDaysBeyond MOD 366)+1; -- one's origin, 366-day year
unpacked.year м gmtBaseYear + 4*fourYears + oddYears;
unpacked.weekday м startWeekday;
THROUGH [0..daysSinceBase MOD 7)
DO unpacked.weekday м SUCC[unpacked.weekday];
IF unpacked.weekday = unspecified
THEN unpacked.weekday м FIRST[DayOfWeek];
ENDLOOP;
FOR month: MonthOfYear IN MonthOfYear[January..December] DO
IF dayOfYear <= monthTable[SUCC[month]] THEN {unpacked.month м month; EXIT};
REPEAT FINISHED => ERROR
ENDLOOP;
unpacked.day м dayOfYear-monthTable[unpacked.month];
unpacked.hour м hrs MOD 24;
{
yearStart: CARDINAL = fourYears * daysInFourYears +
(IF oddYears = 0 THEN 0 ELSE 366 + (oddYears-1)*365);
unpacked.daysThisYear м daysSinceBase - yearStart;
unpacked.secondsThisYear м secs - ((LONG[yearStart] * 24) * 60) * 60;
};
IF unpacked.dst = yes
OR tp.zone = unspecifiedZone
OR NOT CheckDateGE[unpacked, tp.beginDST, 2]
OR CheckDateGE[unpacked, tp.endDST, 1]
THEN EXIT;
hrs м hrs+1;
unpacked.dst м yes;
ENDLOOP;
};

Unpack: PUBLIC PROC [time: GMT] RETURNS [Unpacked] = {
RETURN [UnpackZ[time, GetZoneAndDST[]]];
};

Pack: PUBLIC PROC [unpacked: Unpacked] RETURNS [ time: GMT ] = {
tp: ZoneAndDST = GetZoneAndDST[];
daysInFourYears: CARDINAL = ( 3*365 + 366 );
yearsSinceBase: CARDINAL = IF unpacked.year < gmtBaseYear
THEN ERROR OutOfRange
ELSE unpacked.year - gmtBaseYear;
oddYears: [0..4) = yearsSinceBase MOD 4;
day: CARDINAL = -- day number in year --
monthTable[unpacked.month] + unpacked.day - 1--adjust to zero origin--
- -- monthTable assumes all February's have 29 days, so correct for that --
(IF oddYears#0 AND unpacked.month NOT IN [January..February] THEN 1 ELSE 0);
daysSinceBase: CARDINAL =
(yearsSinceBase/4) * daysInFourYears
+ oddYears * 365 + day
+ (IF oddYears # 0 THEN 1 ELSE 0) --leap day--;
zone: [-720-60..+721] м
IF unpacked.zone # unspecifiedZone
THEN unpacked.zone
ELSE IF tp.zone # unspecifiedZone
THEN tp.zone
ELSE ERROR TimeParametersNotKnown[];
SELECT unpacked.dst FROM
unspecified => {
unpacked.weekday м startWeekday;
THROUGH [0..daysSinceBase MOD 7) DO
unpacked.weekday м SUCC[unpacked.weekday];
IF unpacked.weekday = unspecified THEN
unpacked.weekday м FIRST[DayOfWeek];
ENDLOOP;
IF tp.zone = unspecifiedZone THEN ERROR TimeParametersNotKnown[];
IF CheckDateGE[unpacked,tp.beginDST,2] AND ~CheckDateGE[unpacked,tp.endDST,2]
THEN zone м zone - 60;
};
yes => zone м zone - 60;
no => NULL;
ENDCASE => ERROR;
RETURN [ gmtOrigin + ((LONG[daysSinceBase] * 24 + unpacked.hour) * 60 + unpacked.minute + zone) * 60 + unpacked.second ]
};

CheckDateGE: PROC [unpacked: Unpacked, dstDay, dstHour: CARDINAL] RETURNS [BOOL] = {
day: CARDINAL м monthTable[unpacked.month] + unpacked.day;
SELECT TRUE FROM
day < dstDay-6 => RETURN [FALSE]; -- before the interesting week
day > dstDay => RETURN [TRUE]; -- after the interesting week
unpacked.weekday = Sunday => RETURN [unpacked.hour >= dstHour]; -- critical Sunday
ENDCASE => {
THROUGH DayOfWeek[FIRST[DayOfWeek]..unpacked.weekday) DO
day м day-1;
ENDLOOP; -- calculate day number of preceding Sunday
RETURN [day > dstDay-6] -- before/after the critical Sunday
}
};


secondsPerHour: NAT ~ secondsPerMinute*minutesPerHour;

UnpackPeriod: PUBLIC PROC [period: INT] RETURNS [UnpackedPeriod] ~ {
seconds: CARD ~ ABS[period];
minutes: CARD ~ seconds/secondsPerMinute;
hours: CARD ~ minutes/minutesPerHour;
RETURN [[
hours: hours,
minutes: minutes-hours*minutesPerHour,
seconds: seconds-minutes*secondsPerMinute,
negative: period<0
]];
};
PackPeriod: PUBLIC PROC [period: UnpackedPeriod] RETURNS [seconds: INT] ~ {
part: CARD ~ period.seconds+period.minutes*secondsPerMinute;
IF period.hours<0 THEN ERROR OutOfRange;
IF CARD[period.hours]>(CARD[INT.LAST]-part)/secondsPerHour THEN ERROR OutOfRange;
seconds м part+period.hours*secondsPerHour;
IF period.negative THEN seconds м -seconds;
};

GetTPFromHost: INTERNAL PROC RETURNS [ok: BOOL м TRUE] = {
knownTP м HostTime.GetZoneAndDST[];
knownTPValid м TRUE;
};

SetZoneAndDST: PUBLIC ENTRY PROC [tp: ZoneAndDST] = {
ENABLE UNWIND => NULL;
knownTP м tp;
knownTPValid м TRUE;
};

GetZoneAndDST: PUBLIC ENTRY PROC RETURNS [tp: ZoneAndDST] = {
ENABLE UNWIND => NULL;
IF knownTPValid OR GetTPFromHost[].ok THEN RETURN [knownTP];
RETURN [ BasicTime.unspecifiedTP ];
};

}.
  ─  BasicTimeImpl.mesa:  low-level time facilities
Copyright ╙ 1985, 1986, 1987, 1991 by Xerox Corporation.  All rights reserved.
Russ Atkinson (RRA) July 11, 1988 2:43:53 pm PDT
Hal Murray, June 3, 1986 3:31:31 pm PDT
Doug Wyatt, February 3, 1987 6:15:21 pm PST
Carl Hauser, October 27, 1988 1:56:38 pm PDT
JKF August 30, 1988 5:15:27 pm PDT
Global variables
Sampling this need not be locked because it can only change in ONE direction, and that will only happen after knownTP is set correctly.

Errors
Part I: Fine-grain timer
Part II: Packed times
Returns the time "period" seconds later than "base" (earlier iff "period" is negative).  Raises "OutOfRange" if the result would be before 1968 or after 2036.
Returns time according to the Alto/Pup time standard.  No errors.
Returns time according to the Xerox NS protocol time standard.  No errors.
Accepts time according to the Alto/Pup time standard.  Raises "OutOfRange" for times earlier than 1968.
Accepts time according to the Xerox NS protocol time standard.  Raises "OutOfRange" for times beyond about 2036.
Part III: Packing and unpacking
Raises "OutOfRange" for times before 1968 or after 2036.


Part IV: Finding and setting time and zone/dst information
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