Re: [PATCH] type_from_string_gently: make sure length matches

On Fri, Apr 17, 2015 at 01:54:27PM -0700, Junio C Hamano wrote:

quoted

Since the strings we are matching are literals, we could also record
their sizes in the object_type_strings array and check the length first
before even calling strncmp. I doubt this is a performance hot-spot,
though.

You could also potentially just use strlen(object_type_strings[i]), but
I'm not sure if compilers will optimize out the strlen in this case,
since it is in a loop.

That thought crossed my mind while reading your patch.  It could
even make it go faster if we made object_type_strings into an array
of counted strings (i.e. "struct { const char *str; int len; }")
and then took advantage of the fact that we have lengths of both.

Right, that was what I meant.

I'd be surprised if it appreciably speeds things up, but I guess it is
not too complicated to do.

+static struct {
+	const char *str;
+	int len;
+} object_type_name[] = {
+	{ NULL, 0 },      /* OBJ_NONE = 0 */
+	{ "commit", 6 },  /* OBJ_COMMIT = 1 */
+	{ "tree", 4 },	  /* OBJ_TREE = 2 */
+	{ "blob", 4 },    /* OBJ_BLOB = 3 */
+	{ "tag", 3 },     /* OBJ_TAG = 4 */
 };

I had envisioned a macro like:

  #define SIZED_STRING(x) { (x), (sizeof(x) - 1) }

though perhaps that is overkill for such a short list (that we don't
even expect to change).

-Peff