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From: stever@videovax.UUCP (Steven E. Rice, P.E.)
Newsgroups: net.micro.amiga
Subject: Re: Floating point libraries
Message-ID: <2019@videovax.UUCP>
Date: Thu, 23-Oct-86 19:48:49 EDT
Article-I.D.: videovax.2019
Posted: Thu Oct 23 19:48:49 1986
Date-Received: Sat, 25-Oct-86 06:38:21 EDT
References: <8610160630.AA06315@cory.Berkeley.EDU> <417@husc6.HARVARD.EDU> <432@wuphys.UUCP>
Reply-To: stever@videovax.UUCP (Steven E. Rice, P.E.)
Organization: Tektronix, Comm Group, TV R&D
Lines: 40
Keywords: Fortran, Lattice, AmigaBasic

In article <432@wuphys.UUCP>, Lyle E. Levine (lel@wuphys.UUCP) writes:

> . . .
>             Lattice double:  ~120 sec
> 	    Lattice float:   ~180 sec
>             Basic (double):  140 sec
> 	    Basic (float):   115 sec
> 	    Fortran float:   11.5 sec
> 	    Fortran double:  ~26  sec
> 
> The Fortran math library is IEEE compatible.
> Lattice double is faster than Lattice single since it must pad and
> truncate. What surprized me was the agonizing slowness of their
> floating point calculations. Absoft, on the other hand, clearly
> did a good job of optimizing their
> floating point libraries.  . . .

There may be more here than meets the eye!  It is my recollection that
the IEEE Standard specifies that all operands are to be extended to the
maximum precision of the implementation, the operation(s) performed, and
the result(s) rounded to the final precision using the specified rounding
mode.  Although Lattice seems to take it to an extreme (50% overhead
to extend the operand and round it after seems awfully steep!), the fact
that the Fortran double-precision takes more than twice as long as the
single-precision indicates they are not following this procedure.

Probably what is meant by "IEEE compatible" is that the bits are in
the same place as they are in the IEEE specification.  Although it takes
longer when all computations are performed to the maximum precision of
the implementation, it produces better results.

Cheer up!  The 68881 does this (maximum precision is 80 bits, consisting
of sign, 15-bit exponent, and 64-bit mantissa), and it's blindingly fast.
Any day, now, we'll have 68020s and 68881s in our Amigas, and all these
problems will go away!  (I can dream, can't I?)

					Steve Rice

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