Re: [PATCH][ARM][GAS] Allow integer immediate for VFP vmov instructions.

[Tamar Christina <Tamar dot Christina at arm dot com>]

Hi Nick,

The 05/10/2018 12:16, Nick Clifton wrote:
> Hi Tamar,
> 
> > If the immediate is not a float we convert it and copy it's representation
> > into the imm field and then carry on validating as if we originally entered
> > a floating point immediate.
> 
> I think that you ought to verify that the conversion to floating point 
> representation has not lost any accuracy, and issue a warning/error if
> the floating point and immediate values are not the same.

If there's a significant loss of precision you're going to get an error already due to
is_quarter_float rejecting the float then as it wouldn't be representable.

You also can't have a loss due to a large value, as if the value is large enough not to fit
inside a float it will also not fit in the imm encoding for the instruction, so you'll get
an error saying "garbage after ...".

I have a patch locally that adds a warning using truncf (imm) != imm but have so far been
unable to trigger any failing case.  I can submit it if you'd like to have a warning here
but it also adds a dependency to libm.  I assume that's not a problem?


I assume the AArch64 variant of this patch (submitted at the same time) wouldn't need this
as that just has a more liberal parsing and I don't know whether it was an integer at all.


Regards,
Tamar

> 
> Cheers
>   Nick
> 

--