🚀 go-pugleaf

In article <4jmcnr$lr2@solutions.solon.com> stanr@tiac.net (Stan
Ryckman) writes:

|> In article <4jibl5$89u@solutions.solon.com>,

|> J. Kanze <kanze@gabi-soft.fr> wrote:

|> >BTW, I've found that a small optimizing trick in functions like this can
|> >sometimes work wonders for performance:
|> >
|> >    int
|> >    swap( void* a , void* b , size_t sz )
|> >    {
|> >        unsigned char   buffer[ EXPECTEDMAXSIZE ] ;
|> >        void*           tmp = (sz <= sizeof( buffer ))
|> >                                ? buffer
|> >                                : malloc( sz ) ;

|> Or, if you don't need reentrant or resursive code, you can do:
|> 	static void *tmp = NULL;
|> 	static size_t tmp_sz = 0;

|> 	if (sz > tmp_sz) {
|> 	    .... use realloc here .... you get the idea ....

I wish I'd have thought of this when I actually encountered the problem.
In the real case, the original author of the function had used multiple
returns, and I had a bit of a job finding all of the places where I had
to insert the `free'.  (The original code simply overwrote the rest of
the stack if sz were larger than EXPECTEDMAXSIZE.  Which sort of
explains why I was looking at it in the first place:-).)

|> Details left to the reader (I'm feeling lazy tonight  :)

|> This avoids having to guess what EXPECTEDMAXSIZE might be,
|> but also suffers from never freeing that buffer.  OTOH, it might
|> end up avoiding zillions of calls to malloc if the guess was poor.
|> I've had a couple of thing like that bite when data formats
|> were changed, and I had code inherited from people long-gone.

|> The realloc can certainly do something like use sz+10000
|> to "grow" the tmp area in tunable chunks, depending on the application.

Better yet: unless memory is really tight, have it double the size.
This will set a fairly reasonable upper bound on the number of reallocs
you will have to do.
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
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