Re: [hatari-devel] FPU update

[Douglas Little <doug694@xxxxxxxxxxxxxx>]

Could you describe what errors in attached image mean? I can see that
tested instructions are FCMP and FBOGL but where does those values come
from and why it failed?

fcmp/fbcc:drand

fp result fault @ pc:   $010122f8

opcode sequence:        $f20008b8:$f239a800:$01044cce:$f2940006:

operands:               $3fe421e5adf421e6,$bfd242d1e0d242d2,

expected:               $4006e204dd56e205:fpsr=$08000000

calculated:             $4006e204dd56e206:fpsr=$08000000

fail! (any key to continue)

The operands are used to make the condition:

 fcmp  operand0,operand1

 fbcc  ...

The expected/calculated value has no particular meaning, except that it will be wrong if the wrong fbcc path was taken.

In the sample shown above the fcmp/fbcc and FPSR is ok, but there is a precision/round issue with the arbitrary operation used to make the result. i.e. a problem with some incidental operation. (this is from Hatari 2.00 - lots of failures of this type)

D