René Scharfe <l.s.r@xxxxxx> writes:
> 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.
Depends on whether memcmp is guaranteed to stop immediately on mismatch.
Then memcmp(field, "tree ", 5) cannot walk across a NUL byte in field.
--
David Kastrup
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