Re: [PATCH] type_from_string_gently: make sure length matches
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Apr 17, 2015, 20:54 UTC
- Message-ID
- <xmqqd232pjb0.fsf@gitster.dls.corp.google.com>
- In-Reply-To
- <20150417145247.GA2421@peff.net>
Jeff King <peff@peff.net> writes:
Show 18 quoted lines
> When commit fe8e3b7 refactored type_from_string to allow > input that was not NUL-terminated, it switched to using > strncmp instead of strcmp. But this means we check only the > first "len" bytes of the strings, and ignore any remaining > bytes in the object_type_string. We should make sure that it > is also "len" bytes, or else we would accept "comm" as > "commit", and so forth. > > Signed-off-by: Jeff King <peff@peff.net> > --- > 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.
object.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/object.c b/object.c index aedac24..51584ea 100644 --- a/object.c +++ b/object.c @@ -18,19 +18,22 @@ struct object *get_indexed_object(unsigned int idx) return obj_hash[idx]; } -static const char *object_type_strings[] = { - NULL, /* OBJ_NONE = 0 */ - "commit", /* OBJ_COMMIT = 1 */ - "tree", /* OBJ_TREE = 2 */ - "blob", /* OBJ_BLOB = 3 */ - "tag", /* OBJ_TAG = 4 */ +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 */ }; const char *typename(unsigned int type) { - if (type >= ARRAY_SIZE(object_type_strings)) + if (type >= ARRAY_SIZE(object_type_name)) return NULL; - return object_type_strings[type]; + return object_type_name[type].str; } int type_from_string_gently(const char *str, ssize_t len, int gentle) @@ -40,8 +43,9 @@ int type_from_string_gently(const char *str, ssize_t len, int gentle) if (len < 0) len = strlen(str); - for (i = 1; i < ARRAY_SIZE(object_type_strings); i++) - if (!strncmp(str, object_type_strings[i], len)) + for (i = 1; i < ARRAY_SIZE(object_type_name); i++) + if (object_type_name[i].len == len && + !strncmp(str, object_type_name[i].str, len)) return i; if (gentle)