Re: Building current...

[Johnny Billquist <bqt%update.uu.se@localhost>]

On 2015-12-03 01:27, Johnny Billquist wrote:
> On 2015-12-03 01:09, Christos Zoulas wrote:
> > On Dec 3, 12:01am, bqt%update.uu.se@localhost (Johnny Billquist) wrote:
> > -- Subject: Re: Building current...
> >
> > | => 0x004455ed <+75>:    extzv $0x1f,$0x1,r10,0xfffffff8(fp)
> > |
> > | Hmm, I can't see what's wrong. extzv with those arguments should be ok
> > | according to VARM. But maybe I'm confused...?
> >
> > It
> >
> >
> > http://www2.hmc.edu/www_common/OVMS072-OLD/72final/4515/4515pro_018.html
> >
> > says:
> >
> > -----
> > Opcodes
> >
> > EE    EXTV    Extract Field
> > EF    EXTZV    Extract Zero-Extended Field
> >
> > Description
> >
> > For EXTV, the destination operand is replaced by the sign-extended
> > field specified by the position, size, and base operands. For EXTZV,
> > the destination operand is replaced by the zero-extended field
> > specified by the position, size, and base operands. If the size
> > operand is zero, the only action is to replace the destination
> > operand with zero and to modify the condition codes.
> >
> > Notes
> >
> > 1. A reserved operand fault occurs if:
> >
> >     o size GTRU 32
> >     o pos GTRU 31, size NEQ 0, and the field is contained in the
> > registers
> >
> > On a reserved operand fault, the destination operand is unaffected,
> > and the condition codes are UNPREDICTABLE.
> >
> > -----
> > Here:
> >
> > pos == 31 (0x1f)
> > size != 0 (0x1)
> > field = r10
> >
> > So, the processor is right :-) Now how to figure out what generates
> > this...
>
> GTRU = Greater Than Unsigned. 31 is not greater than 31... :-)

Actually,

extzv $0x1f, $1, r10, -4(sp)

would pretty much be code to set -4(sp) to -1 if r10 is negative, and 
set -4(sp) to 0 if r10 is positive.

	Johnny

--
Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
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