Svante Signell, le Tue 17 Jan 2012 12:37:53 +0100, a écrit :
> On Tue, 2012-01-17 at 11:05 +0100, Samuel Thibault wrote:
> > In addition to that, it might be better for performance to rather
> > remember how much memory was previously allocated, and only reallocate
> > if more memory is needed, and twice as much, so as to reduce the amount
> > of free/malloc calls.
>
> I don't think this kind of optimization is needed for the libtar
> application.
Why? "tar" is a performance-sensitive feature. I guess basename/dirname
is used quite a lot there.
> It definitely complicates the code.
Sure. Optimization often does. As long as it's bearable it's ok and
useful: here it would mean do as described below in the code (which,
unmodified, seems correct to me).
> ==14515== still reachable: 4 bytes in 2 blocks
still reachable, yes, that's not an error. glibc does that in quite a
few places.
> ==14515== suppressed: 0 bytes in 0 blocks
> ==14515== Rerun with --leak-check=full to see details of leaked memory
> ==14515==
> ==14515== For counts of detected and suppressed errors, rerun with: -v
> ==14515== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 4)
> openbsd_basename_new(path)
> const char *path;
> {
> static char *bname = NULL;
static unsigned allocated = 0;
> register const char *endp, *startp;
> int len = 0;
if (!allocated) {
allocated = 64;
bname = malloc(allocated);
if (!bname) {
allocated = 0;
return NULL;
}
}
> /* Empty or NULL string gets treated as "." */
> if (path == NULL || *path == '\0') {
strcpy(bname, ".");
> return(bname);
> }
>
> /* Strip trailing slashes */
> endp = path + len - 1;
> while (endp > path && *endp == '/')
> endp--;
>
> /* All slashes becomes "/" */
> if (endp == path && *endp == '/') {
strcpy(bname, "/");
> return(bname);
> }
>
> /* Find the start of the base */
> startp = endp;
> while (startp > path && *(startp - 1) != '/')
> startp--;
>
> len = endp - startp + 1;
if (len + 1 > allocated) {
unsigned new_allocated = 2 * allocated;
void *new_bname = malloc(new_allocated);
if (!new_bname)
return NULL;
allocated = new_allocated;
free(bname);
bname = new_bname;
}
> (void)strncpy(bname, startp, len);
> bname[len] = '\0';
> return(bname);
> }
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