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From: dillon@CORY.BERKELEY.EDU.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: More ST Floating Point Performance
Message-ID: <8706131920.AA06575@cory.Berkeley.EDU>
Date: Sat, 13-Jun-87 15:20:29 EDT
Article-I.D.: cory.8706131920.AA06575
Posted: Sat Jun 13 15:20:29 1987
Date-Received: Sun, 14-Jun-87 01:43:05 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
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>As far as I know, the Amiga does not "support" the 68881 in any way
>beyond providing an expansion slot.  The 68881 is really only fully
>supported by the 68020 CPU chip.  The "Turbo Amiga" is basically a

	One for me:  The amiga supports the 68881 in the following ways:

	-Automatic detection and setting of a flag bit in Exec library
	-Automatic multi-tasking support (save/restore 68881 registers on
	 task switch).

	Both Lattice and Aztec support a 68881 fp library.

>The Motorola FFP library (and all other 32-bit FP libs) do _NOT_ have
>10-digit precision, only about 6--7 digits.  That is frequently useful
>but just as frequently terrible.  Think about it:  10^10 ~ 2^33, so
>no bits left for the exponent...

	One for you:  24 bits mantissa, 1 bit sign, 7 bit exponent
	Yielding 7.22 digits (base 10) with a nominal exponent range
	-63 to +63.

	However, if that accuracy is good enough for an application, one
	usually uses the IEEE double precision format instead.  This gives
	15-16 digits accuracy with a nominal exponent range -307 to +308

						-Matt