On Tue, Jan 24, 2017 at 12:34:06PM +0000, David Laight wrote:
> From: Marcelo Ricardo Leitner
> > Sent: 23 January 2017 18:48
> > On Mon, Jan 23, 2017 at 11:25:56AM +0000, David Laight wrote:
> > > From: Xin Long
> > > > Sent: 19 January 2017 17:19
> > > > This patch is to implement Sender-Side Procedures for the Add
> > > > Outgoing and Incoming Streams Request Parameter described in
> > > > rfc6525 section 5.1.5-5.1.6.
> > > >
> > > > It is also to add sockopt SCTP_ADD_STREAMS in rfc6525 section
> > > > 6.3.4 for users.
> > > ...
> > > > + out = params->sas_outstrms;
> > > > + in = params->sas_instrms;
> > > > +
> > > > + if (!out && !in)
> > > > + goto out;
> > > > +
> > > > + if (out) {
> > > > + __u16 nums = stream->outcnt + out;
> > >
> > > Make nums 'unsigned int', the code will be smaller and you can
> > > use the value for the overflow check.
> >
> > Smaller as in to avoid the sum below?
> >
> > >
> > > > + /* Check for overflow, can't use nums here */
> > > > + if (stream->outcnt + out > SCTP_MAX_STREAM)
> > > > + goto out;
>
> No, smaller as in not requiring the compiler to add instructions
> to mask (or worse sign extend) the result of the arithmetic expression
> to less than the number of bits in an 'int' when the result of the
> expression is to be kept in a register.
>
> The x86 is about the only modern cpu that has 8 and 16 bit arithmetic.
> For everything else you really don't want to do arithmetic on char
> and short unless you really want the wrapping to happen.
Okay thanks.
Marcelo
