Xref: utzoo comp.lang.misc:3495 comp.arch:11459
Path: utzoo!attcan!utgpu!watmath!att!dptg!rutgers!mailrus!ncar!unmvax!bbx!bbxsda!scott
From: scott@bbxsda.UUCP (Scott Amspoker)
Newsgroups: comp.lang.misc,comp.arch
Subject: Re: Fast conversions, another urban myth?
Message-ID: <136@bbxsda.UUCP>
Date: 21 Sep 89 15:44:37 GMT
References: <832@dms.UUCP> <688@UALTAVM.BITNET> <9dAz02zs58y201@amdahl.uts.amdahl.com> <27935@winchester.mips.COM>
Reply-To: scott@bbxsda.UUCP (Scott Amspoker)
Organization: Basis International,  Albuquerque, NM
Lines: 33

In article <27935@winchester.mips.COM> mash@mips.COM (John Mashey) writes:
 >The REAL question is: how much difference does it really make?
 >Everybody please remember this was a "what-if" analysis, not an
 >analysis that claimed that it really cost 1.6X in performance.
 >At least several vendors who ahve looked at this and did care about
 >COBOL didn't think that it was this much degradation to overall system
 >performance, or at least, in designing their RISCs, included a few
 >simple instructions to help the issue, and chose to stop there.

If I may throw in my $.02 worth:  Decimal arithmetic is alive and
well and not merely an artifact of old COBOL implementations.  We
do everything in C and require decimal arithmetic because of the
business nature of our applications.  It is a constant disappointment
when the scientific-oriented hardware industry forgets that some of
us need to have 100 pennies == 1 dollar.  Interest calculations
carried out to 3 or 4 decimal places need to round correctly.
Converting to binary and back to decimal is not the answer (as
I explained in a previous posting).

Fortunately, business applications are usually I/O bound so the
decimal math can be simulated in software without a perceived
performance penality (unless you bring in an unethical benchmark).

If decimal add and subtract are too costly in the hardware then
why not a simple decimal adjust instruction (like on the 80x86)?
That instruction alone is a great savings when you consider the
software alternatives.  The 3B2 has *nothing* to help decimal
arithmetic.

-- 
Scott Amspoker
Basis International, Albuquerque, NM
(505) 345-5232