On Mittwoch, 10. April 2024 21:36:06 CEST Jody Bruchon wrote: > This patch uses pre-calculated name lengths to massively speed up various > recursive operations. Three new *_fast variant functions are added along > with get_d_namlen copied from libjodycode. Passing lengths allows use of > memcpy() instead of strcpy()/strcat() and replacement of a particularly > hot xasprintf(). Cachegrind shows CPU instructions on Linux x86_64 drop > by 24% to 67% with similar reductions in data reads and writes. > > Anything in BusyBox that uses a while(readdir()) loop or that calls > concat_*path_file() or last_char_is() might benefit from adopting this > optimization framework.
Completely untested, but how about this:
char* FAST_FUNC concat_path_file_fast(const char *path, const struct dirent
*dirp)
{
const char *filename = dirp->d_name;
char *buf;
int end_offset;
int pathlen, namelen;
if (!path) {
path = "";
pathlen = 0;
} else {
pathlen = strlen(path);
if (last_char_is_fast(path, '/', pathlen) == NULL)
pathlen--;
}
namelen = get_d_namlen(dirp);
while (*filename == '/') {
filename++;
namelen--;
}
end_offset = pathlen + 1 + namelen;
buf = (char *)malloc(end_offset + 1);
if (!buf) return NULL;
memcpy(buf, path, pathlen);
*(buf + pathlen) = '/';
memcpy(buf + pathlen + 1, filename, namelen);
*(buf + end_offset) = '\0';
return buf;
}
This avoids scanning an empty path for the trailing slash, and avoids the
check for a trailing slash later entirely, saving one instruction and 2
variables.
You also have quite some places where you have the old code still around and
just commented out, I would have just removed them.
Generally I wonder if the length variables shouldn't be size_t or the like,
which would not affect this function but all of them.
Eike
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