Re: clock, daylight savings time

On Mon, 10 Mar 2008 18:11:39 -0500, William H. Blair wrote:

I believe this is in contrast to the z/OS STCKCONV service.
however, I can not find in the docmentation ("z/OS V1R7.0 MVS
Assembler Services Reference IAR-XCT") whether STCKCONV
returns local time or GMT nor how Daylight Saving and Leap
Seconds are handled (possibly in accord with the table in
the PoOP?) The programmer ought to be given the choice of
either. Perhaps I'll submit an RCF.

STCKCONV returns neither. It returns what it has been given.

If it is given local time, then the result will be local time.

If it is given GMT, then the result will be GMT.

It is just a conversion service, whose input is either a 64-bit
TOD clock value or a 128-bit ETOD clock value.

I'm confused. I thought STCKCONV takes as input a TOD
clock value, and if you operate as IBM recommends, TOD
clock values are always GMT.

To get a TOD clock value corrected for the local time zone and
leap seconds for input to STCKCONV, you would need to execute
code such as this:

TIME STCK,STCKGMT CURRENT GMT TOD CLOCK
STCKCONV STCKVAL=STCKGMT, CONVERT GMT TIME +
CONVVAL=GMTTIMED, TO +
TIMETYPE=DEC, HHMMSSTHMIJU0000 +
DATETYPE=YYYYMMDD YYYYMMDDXXXXXXXX
*
How can the below give the correct result if STCKGMT is read
from a log file written on the other side of a Daylight/Standard
or Leap Second boundary?

L R4,CVTPTR LOAD CVT ADDRESS
USING CVT,R4 CVT ADDRESSABILITY
L R5,CVTEXT2 OS/VS2 COMMON EXTENSION
USING CVTXTNT2,R5 CVTXTNT2 ADDRESSABILITY
LM R14,R15,CVTLDTO DATE/TIME ZONE OFFSET
LM R2,R3,CVTLSO LEAP SECONDS CORRECTION
LM R0,R1,STCKGMT TOD CLOCK STCK VALUE
*
* CALCULATE LOCAL TIME = GMT TOD + CVTLDTO - CVTLSO
*
ALR R1,R15 CORRECT GMT BY LDTO
BC 8+4,TOD1 IF CARRY,
AL R0,=F'1' ADD 1 TO HOW
ALR R0,R14 ADD LDTO HOW
*
TOD1 SLR R1,R3 SUBTRACT LSO LOW
BC 2+1,TOD2 IF NO CARRY,
BCTR R0,0 SUBTRACT 1 FROM HOW
SLR R0,R2 SUBTRACT LSO HOW
*
TOD2 STM R0,R1,STCKLCL TOD CLOCK LOCAL TIME
STCKCONV STCKVAL=STCKLCL, CONVERT LOCAL TIME +
CONVVAL=LCLTIMED, TO +
TIMETYPE=DEC, HHMMSSTHMIJU0000 +
DATETYPE=YYYYMMDD YYYYMMDDXXXXXXXX
LA R1,GMTTIMED
BAS R14,HEXPRT
MVC GMTWTO+12(24),PHEX
LA R1,LCLTIMED
BAS R14,HEXPRT
MVC LCLWTO+12(24),PHEX
WTO MF=(E,GMTWTO) WTO GMT
WTO MF=(E,LCLWTO) WTO LCL

...

HEXPRT UNPK PHEX+00(8+1),00(4+1,R1)
UNPK PHEX+08(8+1),04(4+1,R1)
UNPK PHEX+16(8+1),08(4+1,R1)
TR PHEX+00(24),HEXTAB-C'0'
BR R14

PHEX DS CL25
GMTWTO WTO ' GMT: ....+....1....+....2....',MF=L
LCLWTO WTO ' LOCAL: ....+....1....+....2....',MF=L
STCKGMT DS D
STCKLCL DS D
LCLTIMED DS XL16
GMTTIMED DS XL16
HEXTAB DC C'0123456789ABCDEF'
CVT DSECT=YES CVT map

This produces the following output today (for the Central
Daylight Savings Time Zone) [with punctuation characters
manually inserted]:

GMT: 22:57:14.9007710000 2008/03/10
LOCAL: 15:56:51.9007710000 2008/03/10

The above illustrates the fact that both the LDTO (time zone
offset) and LSO (leap seconds correction factor) have been
PROPERLY taken into account in the calculation of the local
time. Some folks get it wrong. The CVTLDTO field must be
ADDED to the GMT TOD Clock value, but the CVTLSO field must
be SUBTRACTED from the GMT TOD Clock value to get the right
local timestamp.

The programmer ought to be given the choice of either.

Not an issue. It just converts whatever you give it.

Perhaps I'll submit an RCF.

Not a bad idea. It would be nice if the documentation made
clear that it's just a _conversion_ service.

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