Weird timing results in C Post: 302351655

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Top Forums Programming Weird timing results in C Post 302351655 by jim mcnamara on Wednesday 9th of September 2009 07:52:15 AM

09-09-2009

Registered User

Code:

for (; i <= MAXN; i++)
		if ((*foo)(i)) n++;

That iterates MAXN which must be at least 50847534 - for each of the three calls to time_loop() the function ptr is jumping to the same function. Unless that code has to dynamically allocate memory or there is OS contention for some resource, there ought not be those differences.

I happen not to like the static declaration of functions for a variety of reasons except in certain instances-- But that is very probably not the cause of this problem.

You need to call getrusage() before and after - like you now do with clock() to see what is happening in the world of system resources.

Also clock() is just wall time, use the times() function to get system & user time - as consumed by parent & child.

I think shamrock wants to see that you are not calling exec or something else that eats the system resources or causes high kernel times maybe.

jim mcnamara

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request_scroll

request_scroll(3alleg4) 					  Allegro manual					   request_scroll(3alleg4)

NAME

       request_scroll - Queues a hardware scroll request with triple buffering. Allegro game programming library.

SYNOPSIS

       #include <allegro.h>

       int request_scroll(int x, int y);

DESCRIPTION

       This  function  is  used for triple buffering. It requests a hardware scroll to the specified position, but returns immediately rather than
       waiting for a retrace. The scroll will then take place during the next vertical retrace, but you can carry on running  other  code  in  the
       meantime and use the poll_scroll() routine to detect when the flip has actually taken place.

       Triple  buffering  is only possible with certain drivers: you can look at the GFX_CAN_TRIPLE_BUFFER bit in the gfx_capabilities flag to see
       if it will work with the current driver.

RETURN VALUE

       This function returns zero on success, non-zero otherwise.

SEE ALSO

       poll_scroll(3alleg4), request_video_bitmap(3alleg4), gfx_capabilities(3alleg4), scroll_screen(3alleg4)

Allegro 							   version 4.4.2					   request_scroll(3alleg4)

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