RE: [PATCH v2] net: sctp: Don't use 64 kilobyte lookup table for four elements
From: David Laight
Date: Mon Sep 28 2015 - 11:34:09 EST
From: Eric Dumazet
> Sent: 28 September 2015 15:27
> On Mon, 2015-09-28 at 14:12 +0000, David Laight wrote:
> > From: Neil Horman
> > > Sent: 28 September 2015 14:51
> > > On Mon, Sep 28, 2015 at 02:34:04PM +0200, Denys Vlasenko wrote:
> > > > Seemingly innocuous sctp_trans_state_to_prio_map array
> > > > is way bigger than it looks, since
> > > > "[SCTP_UNKNOWN] = 2" expands into "[0xffff] = 2" !
> > > >
> > > > This patch replaces it with switch() statement.
> > What about just adding 1 (and masking) before indexing the array?
> > That might require a static inline function with a local static array.
> > Or define the array as (say)  and just mask the state before using
> > it as an index?
> Just let the compiler do its job, instead of obfuscating source.
> Compilers can transform a switch into an (optimal) table if it is really
> a gain.
The compiler can choose between a jump table and nested ifs for a switch
statement. I've never seen it convert one into a data array index.