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Topic: integer Vs floating point efficiency?
Replies: 13   Last Post: Dec 5, 2012 8:41 PM

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Rui Maciel

Posts: 107
Registered: 11/27/05
Re: integer Vs floating point efficiency?
Posted: Dec 3, 2012 5:03 AM
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Gordon Sande wrote:

> On 2012-12-01 08:41:21 -0400, Rui Maciel said:
>
> Instruction timings etc are to be found in the processor's data sheets.
> Ask the manufacturer of one. The web sites will have copies or request
> pages.


I've followed your advice, and I'm in the process of digesting AMD and
Intel's docs that cover this subject. If anyone is interested, the
documents are available at:

http://support.amd.com/us/psearch/Pages/psearch.aspx?type=2.1%3b2.12&product=2.1.2&contentType=Tech%20Doc%20Processor
http://www.intel.com/content/www/us/en/processors/architectures-software-
developer-manuals.html


Unfortunately, the information isn't compiled or easily accessible. To make
matters worse, I've stumbled on a claim that Intel's docs have been
"incomplete and full of errors", which isn't very reassuring.

Nevertheless, some info on this subject has been compiled by third parties,
such as the following article:

http://www.agner.org/optimize/instruction_tables.pdf


As should be expected, latency varies with the make and model of the
processor, and instruction latency alone doesn't say everything there is to
say (or, possibly, anything) about the inherent efficiency of integer Vs
floating point data types. In addition, there are more than a way to skin
some numerical cats with the AMD64 platform, which adds to the complexity of
this issue.

Nevertheless, from what I gathered so far it appears that, in general,
integer operations do present a small, but possibly entirely meaningless,
efficiency advantage.


Rui Maciel



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