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Full Discussion: Weird timing results in C
Top Forums Programming Weird timing results in C Post 302351886 by CRGreathouse on Thursday 10th of September 2009 01:23:11 AM
Old 09-10-2009
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!).
 

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ppd_emit_to_file(3)					     Library Functions Manual					       ppd_emit_to_file(3)

NAME
ppd_emit_to_file, ppd_emit_to_fd - Output device specific code. SYNOPSIS
#include <ppd/ppd.h> gboolean ppd_emit( PpdFile * ppd,FILE *fp,PpdSectionOrder section ); gboolean ppd_emitfd( PpdFile * ppd, int fd,PpdSectionOrder section ); DESCRIPTION
The ppd_emit_* functions output the device specific code appropriate to the specified section that has not already been emitted.. The PpdFile pointer is obtained from opening a PPD file via the ppd_load(3) family of functions. The section can be any one of the following: PPD_ORDER_ANY Option code can be anywhere in the file PPD_ORDER_DOCUMENT Option code must be in the DocumentSetup section PPD_ORDER_EXIT Option code must be sent prior to the document PPD_ORDER_JCL Option code must be sent as a JCL command PPD_ORDER_PAGE Option code must be in the PageSetup section PPD_ORDER_PROLOG Option code must be in the Prolog section The sections PPD_ORDER_DOCUMENT and PPD_ORDER_PAGE will also output code from the PPD_ORDER_ANY section. Once a code section has been emitted it is marked as such and will not be emitted unless it is re-marked. EXAMPLE
/* Setup code to emitted */ ppd_mark_defaults(ppd); ppd_mark_option(ppd,"Duplex","DuplexNoTumble"); ppd_mark_option(ppd,"PageSize","A4"); /* Emit initial code (including any reset and JCL code) */ ppd_emit_to_file(ppd,stdout,PPD_ORDER_EXIT); fputs(ppd->jcl_begin->str,stdout); ppd_emit_to_file(ppd, stdout, PPD_ORDER_JCL); fputs(ppd->jcl_ps->str, stdout); /* Any header comments go here */ ... /* Prolog section */ printf("%%%%BeginProlog0); ppd_emit_to_file(ppd, stdout, PPD_ORDER_PROLOG); printf("%%%%EndProlog0); /* Setup section */ printf("%%%%BeginSetup0); ppd_emit_to_file(ppd, stdout, PPD_ORDER_DOCUMENT); printf("%%%%EndSetup0); /* Main document begins */ for (...) { printf("%%%%Page: 1 10); /* Re-mark so that this is emitted on each page */ ppd_mark_option(ppd,"PageSize","A4"); printf("%%%%PageSetup0); ppd_emit_to_file(ppd, stdout, PPD_ORDER_PAGE); printf("%%%%EndPageSetup0); /* Page info goes here */ ... } /* Send ending JCL code */ fputs(ppd->jcl_end->str,stdout); SEE ALSO
ppd_file_new(3), ppd_file_free(3) ppd_emit_to_file(3)
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