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From: ggs@ulysses.UUCP (Griff Smith)
Newsgroups: net.unix-wizards
Subject: Re: IBM 1620 10000x10000 digit multiplication
Message-ID: <842@ulysses.UUCP>
Date: Fri, 4-May-84 11:05:06 EDT
Article-I.D.: ulysses.842
Posted: Fri May  4 11:05:06 1984
Date-Received: Sat, 5-May-84 01:24:38 EDT
References: <493@ihuxa.UUCP>, <1347@brl-vgr.ARPA>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 26

Well, I guess it's time for one of the dinosaurs to step in and end
this discussion.  The IBM 1620 did not have a particularly intelligent
multiply algorithm, it fetched the two digits, combined them to create
a decimal address, fetched the product digits from a table in low
memory, then went through two add cycles to add in the product digits,
also using a table in low memory.  The times that I remember are: 20
microsecond memory cycle time, 80 microseconds for an add cycle, 160
microseconds for an instruction fetch/decode cycle.  I am a bit hazy
about the multiply time, but it was within a factor of two of 160
microseconds per cross product.  The product of two 10000 digit numbers
would require about 5 hours of processor time.  For comparison, the
"bignum" code in Franz lisp can do the same thing in about ten seconds
on a VAX 11/780.

The longest thing I ever did on a 1620 was to extract the square roots
of 2 and 5 to 5000 places, which took about 5 hours for each
computation.  Note that this is comparable to the estimate for
multiplication, since square root extraction is about the same speed as
division in the limiting case and division is quite a bit slower than
multiplication.
-- 

Griff Smith	AT&T Bell Laboratories, Murray Hill
Phone:		(201) 582-7736
Internet:	ggs@ulysses.uucp
UUCP:		ulysses!ggs