🚀 go-pugleaf

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Finally I got around to linking the NS32081 floating-point chip I have on my
ST to the Absoft FORTRAN77 run-time library.  (By "linking" I mean patching
the library so that standard FORTRAN code uses the FP chip, transparently.)
Here are _approximate_ timings, all in microseconds:  (32081 clock: 4 MHz).

	op	single precision	double precision

		SWFP	HWFP		SWFP	HWFP

	add	100	 60		160	 75
	mul	130	 60		300	 80
	div	330	 70		900	 90

And here, for what they're worth, are the Savage benchmark results:

System         CPU / FPP    CLOCK        LANGUAGE          TIME     ERROR 
		   	    (MHz)                          (Sec)  Abs(a-2500)

Atari ST     (68000/-----)   8.00   Absoft F77 V2.2         67.6    1.7 E-07
Atari ST     (68000/32081)   8.00   Absoft F77 V2.2         16.3    3.1 E-07

That's faster than a 68020 at 16 MHz without FP chip, and about twice slower
than the 8088/8087 combo at 5 MHz. But note:

(1) - The 32081 is here used as a peripheral, not a coprocessor.  Most of the
      time is spent on the communications, not the calculations!  (And that's
      after I hacked the cartridge port to be able to write to it.  The usual
      trick of writing to that port via the address lines would have resulted
      in much slower performance.)
(2) - The 32081 does NOT have the transcendental functions built-in.  The
      above result is with the Absoft software library calling my hardware
      drivers every time it needs an addition, subtraction, multiplication
      or division.  Thus, a 68881 would do a lot better.

- Moshe Braner