On Wed, Feb 26, 2014 at 10:24:45AM -0800, Joe Perches wrote:
> On Wed, 2014-02-26 at 16:10 +0000, David Laight wrote:
> > From: Alexander Aring
> []
> > > diff --git a/net/ieee802154/6lowpan.h b/net/ieee802154/6lowpan.h
> []
> > > +static inline u8 lowpan_addr_mode_size(const u8 addr_mode)
> > > +{
> > > + switch (addr_mode) {
> > > + case LOWPAN_IPHC_ADDR_00:
> > > + return 16;
> > > + case LOWPAN_IPHC_ADDR_01:
> > > + return 8;
> > > + case LOWPAN_IPHC_ADDR_02:
> > > + return 2;
> > > + default:
> > > + return 0;
> > > + }
> > > +}
> >
> > The compiler will generate much better code if you index an array instead
> > of using a switch statement.
>
> Are you sure of that?
>
> Perhaps the compiler would inline the assignment
> anyway if addr_mode is __builtin_constant_p
>
> gcc 4.8 here does the same thing with:
>
> static inline unsigned char f1(unsigned char a)
> {
> switch (a) {
> case 0: return 16;
> case 1: return 8;
> case 2: return 2;
> default: return 0;
> }
> }
>
> static inline unsigned char f2(unsigned char a)
> {
> static const unsigned char rtns[] = { 16, 8, 2, 0 };
>
> return rtns[a & 3];
> }
to make a mask with & 3 is already done, so we don't need that.
I am not sure what I should do now, change or not change? :-)
- Alex
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