Source code for the time_t time( time_t *timer ) function

bidur · 08-29-2011, 09:42 AM

I am longing to know how the clock ticks are read and then they are stored in the data structure (time_t). I could learn that The time_t is at least 2 bytes long since they store somewhat unique timestamp(with all the year, month, day, hour, second, etc).
I am trying to encode just 24 hours time with as less as possible number of bits. I am able to encode 86400 seconds by using 11 bits, Is it possible to do so by using lesser bits than 11?
For that, I am trying to see how the time is calculated by using the clock ticks information by the standard C function time_t time( time_t *timer ) declared in time.h .
I searched the code for time.h in the ubuntu machine I could find many header files time.h which just declare the time() function with extern keyword. How can I locate the source file location where the actual implementation of the time() function is done.

I am hoping for relevant guidance.

Thanks

Heraton · 08-29-2011, 12:54 PM

Hi there!

First of all, you need to get yourself the kernel sources, because the header files won't tell you what you long to know. That for, you might want to take a closer look at this.

Once you got the kernel sources, a few hundred megabyte of digital wisdom await your exploration. To cut things short, you might want to try something like:

Code:

find /YOUR_SOURCE_CODE_DIRECTORY -name time.c

When it comes to my box, its like

Code:

Me@MYBOX ~/Linux_source/linux-source-2.6.35 $ find ./ -name time.c
./kernel/time.c
./arch/m32r/kernel/time.c
./arch/m68k/kernel/time.c
./arch/m68k/atari/time.c
./arch/m68k/sun3x/time.c
./arch/m68k/hp300/time.c

...and so on...

Here is what made me think this would be a good enty point:

Code:

/*
 *  linux/kernel/time.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  This file contains the interface functions for the various
 *  time related system calls: time, stime, gettimeofday, settimeofday,
 *			       adjtime
 */
/*

I guess, from now on you will have to digg your way on your own. But in case you get stuck, don't hesitate to ask again...

Have fun,

Heraton

bidur · 09-06-2011, 06:07 AM

Dear Friends,
Thanks you for your replies which helped in my understandings.
Also, as I have said earlier in my description that 24 hours can be encoded by 11 bits, I had a calculation error and 11 bits can encode 24 hours not in terms of seconds but in terms of minutes only. For encoding 24 hours in terms of seconds (i.e. 86400 seconds) it requires at least 17 bits. I could not find ways to encode time(86400 seconds) in less than 17 bits.

Thank You