🚀 go-pugleaf

>>> On 25 May 91 22:25:51 GMT, henry@zoo.toronto.edu (Henry Spencer) said:

Henry> I will confine myself to observing that IBM hex FP is the only
Henry> FP format I know of that made half the FP instructions -- the
Henry> single-precision ones -- just about useless to most
Henry> programmers.

I have to point out that the Cyber 205/ETA-10 32-bit FP is worse than
the IBM's hex FP --- at least for the cases I tested.  I discussed
some of this in a paper in Supercomputer in 1987 or 1988 (issue 24, I
believe).  The more interesting part was an analysis of the roundoff
error in the 1000x1000 LINPACK benchmark, which unfortunately did not
make it into the paper in its completed form.

Without looking up my answers in detail, on the 1000x1000 test case,
IEEE machines got 4 significant digits of accuracy, the IBM hex format
got about 3, and the Cyber 205 got 1.   

Since the error is due to rounding modes and truncation, this same
loss of accuracy extends to the 64-bit format, which got about 8
digits of accuracy compared to 12 for IEEE.  This comparison is not
completely fair, since the Cyber 205 64-bit has a bigger exponenent
and smaller mantissa, but the difference is nothing like 4 decimal
digits....
--
John D. McCalpin			mccalpin@perelandra.cms.udel.edu
Assistant Professor			mccalpin@brahms.udel.edu
College of Marine Studies, U. Del.	J.MCCALPIN/OMNET