From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,183ebe04e93f0506
X-Google-Attributes: gid103376,public
X-Google-Thread: 107079,183ebe04e93f0506
X-Google-Attributes: gid107079,public
From: John.A.Limpert.1@gsfc.nasa.gov (John A. Limpert)
Subject: Re: fixed point vs floating point
Date: 1997/11/25
Message-ID: <347b5dee.107124246@news.gsfc.nasa.gov>#1/1
X-Deja-AN: 292674159
References: <mheaney-ya023680002211970739180001@news.ni.net>
 <65846t$4vq$1@gonzo.sun3.iaf.nl>
 <3478ac76.237781@SantaClara01.news.InterNex.Net>
Reply-To: John.A.Limpert.1@gsfc.nasa.gov
Distribution: inet
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
Newsgroups: comp.lang.ada,sci.math.num-analysis
Date: 1997-11-25T00:00:00+00:00
List-Id: <comp.lang.ada>


tmoran@bix.com (Tom Moran) wrote:

>But "type degrees is delta 1.0/16 range 0.0 .. 360.0;" has only 5760
>possible values, and a table lookup with a table of 5760 entries is
>often quite reasonable, and surely faster than converting to fp,
>calculating a sin, and converting back.  Not to mention if the
>function is not just sin, but, say the 6th power of the cos (in a
>Phong illumination calculation, say).

Table lookup has been an important speed optimization for many years,
but does it still work well on newer processors? My experience is that
I don't get the speed improvements that I expect, probably due to the
increasing penalty for cache misses on faster processors. The trend
seems to be that branch-free pipelined code will run faster than table
lookups. Have optimizing compilers kept up with the shifting
tradeoffs?