From: Ingo Molnar <mingo@elte•hu>
To: Erik Faye-Lund <kusmabite@gmail•com>
Cc: "Junio C Hamano" <gitster@pobox•com>,
git@vger•kernel.org, "H. Peter Anvin" <hpa@zytor•com>,
"Thomas Gleixner" <tglx@linutronix•de>,
"Peter Zijlstra" <a.p.zijlstra@chello•nl>,
"Arnaldo Carvalho de Melo" <acme@redhat•com>,
"Frédéric Weisbecker" <fweisbec@gmail•com>,
"Pekka Enberg" <penberg@cs•helsinki.fi>
Subject: Re: [PATCH] git gc: Speed it up by 18% via faster hash comparisons
Date: Thu, 28 Apr 2011 11:33:07 +0200 [thread overview]
Message-ID: <20110428093307.GA15349@elte.hu> (raw)
In-Reply-To: <BANLkTik_2sHZ0OTgQeHpRnpmNsAmT=sAcA@mail.gmail.com>
* Erik Faye-Lund <kusmabite@gmail•com> wrote:
> 2011/4/28 Ingo Molnar <mingo@elte•hu>:
> >
> > * Junio C Hamano <gitster@pobox•com> wrote:
> >
> >> Ingo Molnar <mingo@elte•hu> writes:
> >>
> >> > +static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
> >> > {
> >> > - return !memcmp(sha1, null_sha1, 20);
> >> > + int i;
> >> > +
> >> > + for (i = 0; i < 20; i++, sha1++, sha2++) {
> >> > + if (*sha1 != *sha2) {
> >> > + if (*sha1 < *sha2)
> >> > + return -1;
> >> > + return +1;
> >> > + }
>
> Why not just:
>
> if (*sha1 != *sha2)
> return *sha2 - *sha1;
You mean "*sha1 - *sha2", right?
> memcmp isn't guaranteed to return onlt the values -1, 0, +1, it can
> return any value, just as long as it's sign of a non-zero return
> express the relationship between the first mis-matching byte.
Yeah, agreed, updated patch below. Seems to work fine here.
Ingo
Signed-off-by: Ingo Molnar <mingo@elte•hu>
diff --git a/cache.h b/cache.h
index 2674f4c..574c948 100644
--- a/cache.h
+++ b/cache.h
@@ -675,14 +675,30 @@ extern char *sha1_pack_name(const unsigned char *sha1);
extern char *sha1_pack_index_name(const unsigned char *sha1);
extern const char *find_unique_abbrev(const unsigned char *sha1, int);
extern const unsigned char null_sha1[20];
-static inline int is_null_sha1(const unsigned char *sha1)
+
+static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
{
- return !memcmp(sha1, null_sha1, 20);
+ int i;
+
+ for (i = 0; i < 20; i++, sha1++, sha2++) {
+ if (*sha1 != *sha2)
+ return *sha1 - *sha2;
+ }
+
+ return 0;
}
-static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
+
+static inline int is_null_sha1(const unsigned char *sha1)
{
- return memcmp(sha1, sha2, 20);
+ const unsigned long long *sha1_64 = (void *)sha1;
+ const unsigned int *sha1_32 = (void *)sha1;
+
+ if (sha1_64[0] || sha1_64[1] || sha1_32[4])
+ return 0;
+
+ return 1;
}
+
static inline void hashcpy(unsigned char *sha_dst, const unsigned char *sha_src)
{
memcpy(sha_dst, sha_src, 20);
next prev parent reply other threads:[~2011-04-28 9:36 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-27 22:51 [PATCH] git gc: Speed it up by 18% via faster hash comparisons Ingo Molnar
2011-04-27 23:10 ` Ingo Molnar
2011-04-27 23:18 ` Jonathan Nieder
2011-04-28 6:36 ` Ingo Molnar
2011-04-28 9:31 ` Jonathan Nieder
2011-04-28 10:36 ` Ingo Molnar
2011-04-28 9:32 ` Dmitry Potapov
2011-04-27 23:32 ` Junio C Hamano
2011-04-28 0:35 ` Ralf Baechle
2011-04-28 8:18 ` Bernhard R. Link
2011-04-28 9:42 ` Andreas Ericsson
2011-04-28 9:55 ` Erik Faye-Lund
2011-04-28 20:19 ` H. Peter Anvin
2011-04-28 6:27 ` Ingo Molnar
2011-04-28 9:17 ` Erik Faye-Lund
2011-04-28 9:33 ` Ingo Molnar [this message]
2011-04-28 9:37 ` Ingo Molnar
2011-04-28 9:50 ` Erik Faye-Lund
2011-04-28 10:10 ` Pekka Enberg
2011-04-28 10:19 ` Erik Faye-Lund
2011-04-28 10:30 ` Pekka Enberg
2011-04-28 11:59 ` Erik Faye-Lund
2011-04-28 12:12 ` Pekka Enberg
2011-04-28 12:36 ` Jonathan Nieder
2011-04-28 12:40 ` Erik Faye-Lund
2011-04-28 13:37 ` Ingo Molnar
2011-04-28 15:14 ` Ingo Molnar
2011-04-28 16:00 ` Erik Faye-Lund
2011-04-28 20:32 ` Ingo Molnar
2011-04-29 7:05 ` Alex Riesen
2011-04-29 16:24 ` H. Peter Anvin
2011-04-28 12:16 ` Tor Arntsen
2011-04-28 20:23 ` H. Peter Anvin
2011-04-28 12:17 ` Andreas Ericsson
2011-04-28 12:28 ` Erik Faye-Lund
2011-04-28 10:19 ` Ingo Molnar
2011-04-28 12:02 ` Nguyen Thai Ngoc Duy
2011-04-28 12:18 ` Erik Faye-Lund
2011-04-28 20:20 ` Junio C Hamano
2011-04-28 16:36 ` Dmitry Potapov
2011-04-28 8:52 ` Dmitry Potapov
2011-04-28 9:11 ` Ingo Molnar
2011-04-28 9:31 ` Dmitry Potapov
2011-04-28 9:44 ` Ingo Molnar
2011-04-28 9:38 ` Ingo Molnar
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