Weird timing results in C Post: 302351886

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Top Forums Programming Weird timing results in C Post 302351886 by CRGreathouse on Thursday 10th of September 2009 01:23:11 AM

09-10-2009

Registered User

Nothing funny, just bit manipulation and accessing a big array. The functions are all similar and all display the same results; here's one example:

Code:

#define GET(b) ((sieve[(b)>>5]>>((b)&31))&1)
static int isprime3(int p) { return (p&1) ? p > 2 && !GET(p >> 1) : p == 2; }

The system is 32-bit Xubuntu 8.10 on a quad-core Phenom II.

As I said before, the results are consistent. When I call

Code:

	printf("New:     %f s\n", median3(&isprime3));
	printf("New:     %f s\n", median3(&isprime3));
	printf("New:     %f s\n", median3(&isprime3));

the time for the first, fourth, and seventh times are fast, the times for the third, sixth, and ninth times are slow, etc.

---------- Post updated at 01:23 AM ---------- Previous update was at 01:18 AM ----------

Quote:

Originally Posted by jim mcnamara

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.

I don't do it much. If you have advice on better ways to do it, feel free to expound (or give a link!).

CRGreathouse

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LEARN ABOUT CENTOS

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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