Re: [hatari-devel] Re: [issue18062] m68k FPU precision issue

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

Are there any Atari demos or programs that rely on 80-bit
FPU precision mode?


	- Eero

PS. EmuTOS throws line-F exception with the test program for this.

--- Begin Message ---

• To: debian-68k@xxxxxxxxxxxxxxxx
• Subject: Re: [issue18062] m68k FPU precision issue
• From: Laurent Vivier <Laurent@xxxxxxxxx>
• Date: Sun, 26 May 2013 21:26:19 +0200
• Old-return-path: <Laurent@xxxxxxxxx>

Le 26/05/2013 19:44, Thorsten Glaser a écrit :

Eero Tamminen dixit:

Now as additional data point, UAE/WinUAE/etc. would be interesting.

I built the test with fpu_control.h header from eglibc, using
Sparemint GCC 2.9.5 (with 2010 binutils) and MiNTlib.  When it's

Nice ;)

I.e. it seems that WinUAE FPU emulation is also lacking FPUCW change
handling (for precision).

(Hatari's WinUAE CPU core code was synched with upstream last year.)

OK, thanks. I’d just say let’s say changing FPU precision is not
part of the target we support. (Funnily enough, ColdFire according
to the ’net has (unchangeable) 64-bit precision… maybe let’s just
say precision on m68k in general is not defined.)

m68k has 32, 64 and 80 bit precision [1]. Internally all computing are done with a mantissa of 67-bit and a 16-bit exponent (17 on 68882/68881) [2]. If I remember correctly, last time I checked, Aranym was using internally only 64bit floating point type (like coldfire).

Regards,
Laurent

"MOTOROLA M68000 FAMILY Programmer’s Reference Manual (includes CPU32 instructions)"

[1] "1.5.2 Binary Floating-Point Formats"
[2] "3.5.1 Intermediate Result"


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--- Begin Message ---

• To: Tuomas Vainikka <tuomas.vainikka@xxxxxxxxxxx>
• Subject: Re: [issue18062] m68k FPU precision issue
• From: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
• Date: Sun, 26 May 2013 21:15:35 +0200
• Cc: debian-68k@xxxxxxxxxxxxxxxx
• Old-return-path: <whitebox@xxxxxxxxxx>

Tuomas Vainikka <tuomas.vainikka@xxxxxxxxxxx> writes:

> Is there a difference between 040 FPU and the 68881 in how many bits of
> excess precision things get calculated?

No.

> IIRC there was a difference between 040 and 68881 in gcc with how
> -fexcess-precision was handled...

The only difference between 68881/2 and 68040+ is that the latter
supports extra insns with implicit rounding mode.

Andreas.

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