Am 12.03.2014 20:39, schrieb Junio C Hamano:
Jeff King <peff@xxxxxxxx> writes:static inline int standard_header_field(const char *field, size_t len) { - return ((len == 4 && !memcmp(field, "tree ", 5)) || - (len == 6 && !memcmp(field, "parent ", 7)) || - (len == 6 && !memcmp(field, "author ", 7)) || - (len == 9 && !memcmp(field, "committer ", 10)) || - (len == 8 && !memcmp(field, "encoding ", 9))); + return ((len == 4 && starts_with(field, "tree ")) || + (len == 6 && starts_with(field, "parent ")) || + (len == 6 && starts_with(field, "author ")) || + (len == 9 && starts_with(field, "committer ")) || + (len == 8 && starts_with(field, "encoding ")));These extra "len" checks are interesting. They look like an attempt to optimize lookup, since the caller will already have scanned forward to the space.
I wonder what the performance impact might be. The length checks are also needed for correctness, however, to avoid running over the end of the buffer.
If one really wants to remove the magic constants from this, then one must take advantage of the pattern len == strlen(S) - 1 && !memcmp(field, S, strlen(S)) that appears here, and come up with a simple abstraction to express that we are only using the string S (e.g. "tree "), length len and location field of the counted string.
This might be a job for kwset. René -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html