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Date:         Wed, 25 Feb 2004 08:19:58 -0500
Reply-To:     "Fehd, Ronald J. (PHPPO)" <rjf2@CDC.GOV>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Fehd, Ronald J. (PHPPO)" <rjf2@CDC.GOV>
Subject:      Re: Floating point storage of missing values
Content-Type: text/plain; charset="us-ascii"

Dennis's comment: "to use only floating point numbers as variables" i.e. real numbers prompts me to ask: Has anyone done any testing of the SAS set of missing values -- . ._ .A--.Z -- in numeric variables whose length is less than 8 bytes?

Ron Fehd the macro maven CDC Atlanta GA USA RJF2@cdc.gov Efficiency is intelligent laziness. -David Dunham

> -----Original Message----- > From: Dennis Diskin [mailto:diskin.dennis@KENDLE.COM] > Sent: Wednesday, February 25, 2004 7:38 AM > To: SAS-L@LISTSERV.UGA.EDU > Subject: Re: Floating point storage of missing values > > > Mike, > > You've already had a lot of good responses regarding actual > order of the missing values. I just thought I'd point out > that the binary represnetation will depend on your hardware. > SAS's imlpementation of missing is tied in to their decision > to use only floating point numbers as variables. Though it > varies in implementation, a floating point number is stored > as a characteristc and a mantissa (exponent and base). On the > hardware I am familiar with, the mantissa porition is > normalized (ie. left > justified) and zeros are stored as all zero bits. If you > create a binary representation which does not fall into the > normalized representation, it is not a valid floating point > number. When you try to floating point arithmetic on one of > these, the hardware generates an interrupt which can be > trapped and handled as you wish. This is where the overhead > comes in. Just testing for order probably does not generate > the interrupt since it is usually done on a binary basis.


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