Integers was:RE: [AccessD] Global Variable

John W. Colby jwcolby at colbyconsulting.com
Wed May 18 20:30:16 CDT 2005


The second may be true (though I doubt it since there are native
instructions for math operations on 16 bit registers) but the first is
almost certainly not true.  It is almost certainly the case that an
instruction to load an 8 or 16 bit value takes no longer than one that loads
a 32 bit value, and all three are just a single instruction.

http://www.cs.tut.fi/~siponen/upros/intel/

Will allow you to see the register names, sizes and uses, how many clock
cycles it takes to perform various memory and register operations, the sizes
of the instructions, and tons of more arcane information if you have any
interest in that stuff.  This is for the 486 and previous but the concepts
extend into modern processors as well. 

John W. Colby
www.ColbyConsulting.com 

Contribute your unused CPU cycles to a good cause:
http://folding.stanford.edu/

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Stuart McLachlan
Sent: Wednesday, May 18, 2005 7:03 PM
To: Access Developers discussion and problem solving
Subject: Re: Integers was:RE: [AccessD] Global Variable


On 18 May 2005 at 10:48, Francisco Tapia wrote:

> I was always under the impression that a 16bit integer was processed 
> in a
> single clock cycle just like the 32bit long integer. Additionally a 16bit 
> integer always took up less memory. Have I been led astray from all the 
> various tech magazines and discussion lists around the net?
> 

The arithmetic is processed in the same number of cycles. It's accessing 
the data in memory and returning the result that takes up takes the 
additional steps and adds extra cycles if the variable is not "native" in 
size (ie 32 bit on a 32 bit processor).

Secondly,  generally a compiler can't optimize loops, array indices etc by 
storing the variable as a "register variable" unless it is a "native int".



  



-- 
Stuart


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