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];
}
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