Re: Neat article on number systems

[GLS@MIT-AI]

CC: GLS at MIT-AI, BKPH at MIT-AI, MARR at MIT-AI

See the March 1979 issue of Communications of the ACM, page 166:
"FOCUS Microcomputer Number System", by Edgar and Lee.  It has a
nice exposition and analysis (though the explanation of the "16-bit"
case is fuzzy) of doing "real" arithmetic by using sign plus
a logarithm expressed as a fixed-point fraction.  They have an
interesting technique for doing addition of numbers represented
by logarithms.  They claim that using an eight-bit FOCUS number
provides the range and resolution of a 15 7/8-bit fixed-point number,
and that a 16-bit FOCUS number compares favorably with 18-bit
floating-point.  An 8-bit FOCUS number, they claim, has less inherent
audible noise than high-quality recording tape (they have in mind
audio processing applications on an 8080).  Anyway, check it out.
It may be a useful number format to have on the LISP Machine, say;
one could get many FOCUS numbers into an ART-16 or ART-8 array.
-- Quux