From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: 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 12:39:01 -0700 [thread overview]
Message-ID: <xmqqiorjky0a.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <20140312175624.GA7982@sigill.intra.peff.net> (Jeff King's message of "Wed, 12 Mar 2014 13:56:24 -0400")
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.
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.
Blindly replacing starts_with() with !memcmp() in the above part is
a readability regression otherwise.
> ... I
> think with a few more helpers we could really further clean up some of
> these callsites.
Yes.
next prev parent reply other threads:[~2014-03-12 19:39 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 [this message]
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
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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