Am 12.03.2014 20:39, schrieb Junio C Hamano:
Jeff King <p...@peff.net> 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
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