[FFmpeg-devel] [PATCH 0/2] Origin Wing Commander IV video decoder

[Kostya]

On Thu, Feb 03, 2011 at 02:27:55PM +0000, M?ns Rullg?rd wrote:
> Diego Biurrun <diego at biurrun.de> writes:
> 
> > On Thu, Feb 03, 2011 at 01:54:42PM +0000, M?ns Rullg?rd wrote:
> >> Benoit Fouet <benoit.fouet at free.fr> writes:
> >> > On Thu, 03 Feb 2011 14:02:12 +0100 Diego Biurrun wrote:
> >> >> On Thu, Feb 03, 2011 at 01:28:23PM +0100, Benoit Fouet wrote:
> >> >> > On Thu, 03 Feb 2011 12:30:17 +0100 Diego Biurrun wrote:
> >> >> > > On Thu, Feb 03, 2011 at 10:32:25AM +0100, Kostya wrote:
> >> >> > > > +static int xan_unpack_luma(const uint8_t *src, int src_size, uint8_t *dst, int dst_size)
> >> >> > > 
> >> >> > > Long line; src_size and dst_size should be const.
> >> >> > > 
> >> >> > > > +   uint8_t *dst_end = dst + dst_size;
> >> >> > > > +   const uint8_t *src_end = src + src_size;
> >> >> > > 
> >> >> > > dst_end should be const as well.
> >> >> > > 
> >> >> > > > +/* almost the same as in xan_wc3 decoder */
> >> >> > > > +static int xan_unpack(uint8_t *dest, int dest_len, const uint8_t *src, int src_len)
> >> >> > > 
> >> >> > > Long line; dest_len and src_len should be const.
> >> >> > 
> >> >> > There is very little point in having them const.  Could you clarify why
> >> >> > you want them to be?
> >> >> 
> >> >> I'm somewhat surprised by your question - because they are not changed
> >> >> inside the function?  Was there ever another reason to declare something
> >> >> const?
> >> >
> >> > And even though they were changed, why would that matter anyway?
> >> > You're passing a value to the function, you don't care about it being
> >> > modified or not. Do you really think that that will save 2 registers
> >> > (or 2 int in the stack) when compiled with a const?
> >> 
> >> There is indeed not much point declaring parameter values as const.
> >> The only advantage it brings is that the compiler will flag an error
> >> if you accidentally modify them.
> >
> > That's all I was trying to achieve.  Marking as much stuff as possible
> > const is a good habit to pick up IMO.
> 
> It depends.  Over-zealous application of const to parameter values can
> come back to bite you.  Suppose you later want to change the code such
> that it does modify the value (still no change visible from the
> caller).  Then you must drop the const, and this change can have
> cascade effects if dealing with an interface with multiple
> implementations, such as through function pointers.  I've been through
> all that, and it's not fun.

Ahem, this seems to form a nice bikeshed.
 
> -- 
> M?ns Rullg?rd
> mans at mansr.com