Re: [PATCH] target/ppc: Fix 64-bit decrementer

[Peter Maydell]

On Mon, 13 Sept 2021 at 19:09, Luis Fernando Fujita Pires
<luis.pires@eldorado.org.br> wrote:
>
> > >     value = extract64(value, 0, nr_bits);
> > >     value = ((target_long)value << (64 - nr_bits)) >> (64 - nr_bits);
> >
> > Oops, sorry. 64 might not be correct here. It would depend on the target 
> > being
> > either 32 or 64.
>
> In fact, sextract already does the sign extension, so this should be all 
> that's needed, right?
>     value = sextract<32,64>(value, 0, nr_bits);

Indeed, sextract64() is the preferred way to do a sign extension.

(The one thing to watch out for is that you mustn't try to
extract a zero-width field; it will assert if you do.
It also asserts if you specify a field whose start,length
would put either end to the left of bit 63 or the right of
bit 0, but that's less likely than the zero-width case.)

-- PMM