Re: [PATCH 2/5] powerpc: Replace _ALIGN_DOWN() by ALIGN_DOWN()

[Segher Boessenkool]

Hi!

On Tue, Apr 21, 2020 at 01:04:05AM +0000, Joel Stanley wrote:
> On Mon, 20 Apr 2020 at 18:38, Christophe Leroy <christophe.leroy@xxxxxx> wrote:
> > _ALIGN_DOWN() is specific to powerpc
> > ALIGN_DOWN() is generic and does the same
> >
> > Replace _ALIGN_DOWN() by ALIGN_DOWN()
> 
> This one is a bit less obvious. It becomes (leaving the typeof's alone
> for clarity):
> 
> -((addr)&(~((typeof(addr))(size)-1)))
> +((((addr) - ((size) - 1)) + ((typeof(addr))(size) - 1)) &
> ~((typeof(addr))(size)-1))
> 
> Which I assume the compiler will sort out?

[ This is line-wrapped, something in your mailer?  Took me a bit to figure
  out the - and + are diff -u things :-) ]

In the common case where size is a constant integer power of two, the
compiler will have no problem with this.  But why do so complicated?

Why are the casts there, btw?


Segher