Which is more expensive ? Post: 302131762

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Top Forums Programming Which is more expensive ? Post 302131762 by Perderabo on Monday 13th of August 2007 03:39:02 PM

08-13-2007

Administrator Emeritus

I would code your first snippet but compile with an optimizer. These days optimizers will unroll loops if unrolling is advantageous. That particular loop is not a real great candidate for unrolling anyway. A better candidate would be:

for(i=0; i<100; i++) A[i]=0;

Most superscalar cpus can execute:
A[i]=0;
A[i+1]=0;
A[i+2]=0;
simultaneously. How deep it can go depends on the cpu and that's why leaving unrolling to an optimizer is a good idea. The optimizer should know the target cpu. But your case involved a system call which is different. You're only saving some loop overhead.

Apparently, if you explicitly unroll a loop when it is not advantageous, most optimizers will not reroll the loop. At least this was the case circa 1998 when my copy of "High Performance Computing" was published. If you have that book, see chapter 8, "Loop Optimizations" and chapter 9, "Understanding Parallelism". This is still a great book and it's not just for Fortran programmers.

Anyway, if you are not in control of which fd's might be open, you need to to loop up to OPEN_MAX closing them. High fd's might have been opened and then setrlimit() called lower to the max fd.

Perderabo

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graphics::primitive::insets

Graphics::Primitive::Insets(3pm)			User Contributed Perl Documentation			  Graphics::Primitive::Insets(3pm)

NAME

       Graphics::Primitive::Insets - Space between things

DESCRIPTION

       Graphics::Primitive::Insets represents the amount of space that surrounds something.  This object can be used to represent either padding
       or margins (in the CSS sense, one being inside the bounding box, the other being outside)

SYNOPSIS

	 use Graphics::Primitive::Insets;

	 my $insets = Graphics::Primitive::Insets->new({
	   top	   => 5,
	   bottom  => 5,
	   left    => 5,
	   right   => 5
	 });

METHODS

   Constructor
       new Creates a new Graphics::Primitive::Insets.

   Instance Methods
       as_array
	   Return these insets as an array in the form of top, right, bottom and left.

       bottom
	   Set/Get the inset from the bottom.

       equal_to
	   Determine if these Insets are equal to another.

       left
	   Set/Get the inset from the left.

       right
	   Set/Get the inset from the right.

       top Set/Get the inset from the top.

       zero
	   Sets all the insets (top, left, bottom, right) to 0.

AUTHOR

       Cory Watson, "<gphat@cpan.org>"

SEE ALSO

       perl(1)

COPYRIGHT &; LICENSE
       Copyright 2008-2010 by Cory G Watson.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.12.3							    2010-08-21					  Graphics::Primitive::Insets(3pm)