From: David Kastrup <dak@gnu.org>
To: "René Scharfe" <l.s.r@web.de>
Cc: Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
Quint Guvernator <quintus.public@gmail.com>,
git@vger.kernel.org
Subject: Re: [PATCH] general style: replaces memcmp() with proper starts_with()
Date: Wed, 12 Mar 2014 22:16:13 +0100 [thread overview]
Message-ID: <87fvmni0de.fsf@fencepost.gnu.org> (raw)
In-Reply-To: <5320C8CC.3010404@web.de> ("René Scharfe"'s message of "Wed, 12 Mar 2014 21:51:24 +0100")
René Scharfe <l.s.r@web.de> writes:
> Am 12.03.2014 20:39, schrieb Junio C Hamano:
>> Jeff King <peff@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.
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
next prev parent reply other threads:[~2014-03-12 21:16 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-12 14:43 [PATCH] general style: replaces memcmp() with proper starts_with() Quint Guvernator
2014-03-12 17:56 ` Jeff King
2014-03-12 19:39 ` Junio C Hamano
2014-03-12 19:49 ` Jeff King
2014-03-12 20:08 ` Junio C Hamano
2014-03-12 21:14 ` Jeff King
2014-03-12 21:39 ` Jeff King
2014-03-12 22:06 ` Jeff King
2014-03-12 22:38 ` Junio C Hamano
2014-03-13 3:33 ` Quint Guvernator
2014-03-13 17:46 ` Junio C Hamano
2014-03-14 4:57 ` Jeff King
2014-03-14 14:51 ` Quint Guvernator
2014-03-14 16:56 ` Junio C Hamano
2014-03-12 20:51 ` René Scharfe
2014-03-12 21:16 ` David Kastrup [this message]
2014-03-12 21:45 ` René Scharfe
2014-03-12 20:52 ` David Kastrup
2014-03-12 22:37 ` Junio C Hamano
2014-03-13 6:27 ` David Kastrup
2014-03-13 17:47 ` Junio C Hamano
2014-03-13 17:55 ` Jeff King
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