Converting a STCK into Unix time

A system z STCK instruction gives the number of microseconds since Jan 1st 1900. The Unix time is based on Jan 1st 1970.

I needed to convert a STCK to a Unix time.

Convert a STCK to seconds and microseconds.

Bit 51 of the STCK instructions represents 1 microsecond.

// get the STCK value 
unsigned long long stck, stck2;
 __stckf(&stck); // use store clock fast 

// convert STCK to microseconds 
stck2 = stck >>12; 
int seconds = stck2/1000000; // 1 million
int microseconds = stck2%1000000

Because the STCK will overflow on September 17, 2042, you should be using the STCKE instruction.  The format of the STCKE is a one byte epoch, the STCK value, and other data.

To get the time in seconds

unsigned long longstck4
char stcke[16]; 
 __stcke(&stcke); 
memcpy(&stck4,&stcke,8); // only get the relevant part
stck4 = stck4>>4; // shift it 4, (STCK shifts 12)
seconds= stck4/1000000; 

Get the unix time

time_t t =  time(); 

This time will overflow on January 19, 2038.

You can use

#define _LARGE_TIME_API 
#include <time.h> 
... 
time64_t t64 ; 
time64(&t64); 

and t64 is a long long integer.

Converting STCK seconds to Unix time

UnixSeconds = STCKSeconds – 2208988800;

and the number of micro seconds is the same.

Format it

To format it see here.