Re: [hatari-devel] Beams TT demo FPU warnings

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 08/02/2017 07:37 PM, Toni Wilen wrote:
> > It would be good to have a test program reporting all the possible
> > FPU constant values. People owning TT machines could then run it
> > and report the values they get from their 68882 FPUs, so that we
> > can see whether the mask sets actually differed in reality.  Or
> > just add one of those sets to Hatari.
>
> I dumped 68882 contents and most undocumented fields are zeros.
> 68881 output is also needed (I only have 68882s).

TTs have builtin 68882, so that's enough.  Other Atari machines
didn't include FPU so they could have either model (if any).


> This does not match
> documentation ("constants useful only to the on-chip microcode
> routines"), so perhaps 68881 has more non-zero values?

According to spec text, only for M68040FPSP non-specified index
values could be expected to be zeros.


> This is what 68882 returns

Nicolas, would it make sense to include these to Hatari?


> (Using dump program that someone made ages
> ago, I don't remember what < or > mean)

Those values are for different variants of irrational numbers
or very large numbers which cannot be represented exactly by
floating point.  I assume < & > just mean in which direction
the constant (marginally) differs from the real value.


> 0   $00 < 0x40000000C90FDAA22168C235 (3.14159)
> 1   $01   0x40010000FE00068200000000 (7.9375)
> 2   $02   0x40010000FFC0050380000000 (7.99219)
> 3   $03   0x200000007FFFFFFF00000000 (NaN0.000000)
> 4   $04   0x00000000FFFFFFFFFFFFFFFF (0)
> 5   $05   0x3C000000FFFFFFFFFFFFF800 (2.22507e-308)
> 6   $06   0x3F800000FFFFFF0000000000 (1.17549e-38)
> 7   $07   0x00010000F65D8D9C00000000 (NaN0.000000)
> 8   $08   0x7FFF0000401E000000000000 (NaN0.000000)
> 9   $09   0x43F30000E000000000000000 (7.68057e+304)
> 10  $0A   0x40720000C000000000000000 (6.23076e+34)
> 11  $0B > 0x3FFD00009A209A84FBCFF798 (0.30103)
> 12  $0C > 0x40000000ADF85458A2BB4A9A (2.71828)
> 13  $0D < 0x3FFF0000B8AA3B295C17F0BC (1.4427)
> 14  $0E   0x3FFD0000DE5BD8A937287195 (0.434294)
> 15  $0F   0x000000000000000000000000 (0)
> 16  $10   0x000000000000000000000000 (0)
> 17  $11   0x000000000000000000000000 (0)
> 18  $12   0x000000000000000000000000 (0)
> 19  $13   0x000000000000000000000000 (0)
> 20  $14   0x000000000000000000000000 (0)
> 21  $15   0x000000000000000000000000 (0)
> 22  $16   0x000000000000000000000000 (0)
> 23  $17   0x000000000000000000000000 (0)
> 24  $18   0x000000000000000000000000 (0)
> 25  $19   0x000000000000000000000000 (0)
> 26  $1A   0x000000000000000000000000 (0)
> 27  $1B   0x000000000000000000000000 (0)
> 28  $1C   0x000000000000000000000000 (0)
> 29  $1D   0x000000000000000000000000 (0)
> 30  $1E   0x000000000000000000000000 (0)
> 31  $1F   0x000000000000000000000000 (0)
> 32  $20   0x000000000000000000000000 (0)
> 33  $21   0x000000000000000000000000 (0)
> 34  $22   0x000000000000000000000000 (0)
> 35  $23   0x000000000000000000000000 (0)
> 36  $24   0x000000000000000000000000 (0)
> 37  $25   0x000000000000000000000000 (0)
> 38  $26   0x000000000000000000000000 (0)
> 39  $27   0x000000000000000000000000 (0)
> 40  $28   0x000000000000000000000000 (0)
> 41  $29   0x000000000000000000000000 (0)
> 42  $2A   0x000000000000000000000000 (0)
> 43  $2B   0x000000000000000000000000 (0)
> 44  $2C   0x000000000000000000000000 (0)
> 45  $2D   0x000000000000000000000000 (0)
> 46  $2E   0x000000000000000000000000 (0)
> 47  $2F   0x000000000000000000000000 (0)
> 48  $30 < 0x3FFE0000B17217F7D1CF79AC (0.693147)
> 49  $31 < 0x40000000935D8DDDAAA8AC17 (2.30259)
> 50  $32   0x3FFF00008000000000000000 (1)
> 51  $33   0x40020000A000000000000000 (10)
> 52  $34   0x40050000C800000000000000 (100)
> 53  $35   0x400C00009C40000000000000 (10000)
> 54  $36   0x40190000BEBC200000000000 (1e+08)
> 55  $37   0x403400008E1BC9BF04000000 (1e+16)
> 56  $38 < 0x406900009DC5ADA82B70B59E (1e+32)
> 57  $39 > 0x40D30000C2781F49FFCFA6D5 (1e+64)
> 58  $3A < 0x41A8000093BA47C980E98CE0 (1e+128)
> 59  $3B < 0x43510000AA7EEBFB9DF9DE8E (1e+256)
> 60  $3C < 0x46A30000E319A0AEA60E91C7 (Inf)
> 61  $3D > 0x4D480000C976758681750C17 (Inf)
> 62  $3E < 0x5A9200009E8B3B5DC53D5DE5 (Inf)
> 63  $3F < 0x75250000C46052028A20979B (Inf)
>
> (64 - 127 is same as 0 to 63 so mask should be 0x3f, not 0x7f. Unless
> 68881 works differently)

The lowest 7 bits in the instruction are for ROM index, so
I think the mask in WinAUE code is correct.  Emulator could
map the higher values to 0 though.


	- Eero