From: Alex Gramiak <agrambot@gmail.com>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: Eli Zaretskii <eliz@gnu.org>, emacs-devel@gnu.org
Subject: Using SMALL_LIST_LEN_MAX for memq and list_length (was: [RFC] Some new vector procedures (vector-{memq, apply, to-string, ...}))
Date: Sat, 20 Apr 2019 21:01:13 -0600 [thread overview]
Message-ID: <8736mc6ozq.fsf_-_@gmail.com> (raw)
In-Reply-To: <ce8e3728-ccf7-de87-8fdc-fad9e404cc32@cs.ucla.edu> (Paul Eggert's message of "Sat, 20 Apr 2019 15:54:50 -0700")
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Paul Eggert <eggert@cs.ucla.edu> writes:
> We could probably speed up the cycle checking somewhat, but that's a different
> topic.
On that topic, I recently tried using SMALL_LIST_LEN_MAX for memq and
list_length similarly to nth/elt. WDYT? For small lists it seems to be
faster, but for longer lists it seems to be slower (maybe that's due to
the branch predictor in my simple benchmark-run-compiled tests).
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diff --git a/src/fns.c b/src/fns.c
index c3202495da..267bd2c40f 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -1557,9 +1557,18 @@ The value is actually the tail of LIST whose car is ELT. */)
(Lisp_Object elt, Lisp_Object list)
{
Lisp_Object tail = list;
+ for (int i = 0; i < SMALL_LIST_LEN_MAX; ++i, tail = XCDR (tail))
+ {
+ if (!CONSP (tail))
+ goto end;
+ else if (EQ (XCAR (tail), elt))
+ return tail;
+ }
+
FOR_EACH_TAIL (tail)
if (EQ (XCAR (tail), elt))
return tail;
+ end:
CHECK_LIST_END (tail, list);
return Qnil;
}
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diff --git a/src/fns.c b/src/fns.c
index c3202495da..b7f25d4cba 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -97,6 +97,11 @@ ptrdiff_t
list_length (Lisp_Object list)
{
intptr_t i = 0;
+ for ( ; i < SMALL_LIST_LEN_MAX && CONSP (list); ++i, list = XCDR (list))
+ ;
+ if (i < SMALL_LIST_LEN_MAX)
+ return i;
+
FOR_EACH_TAIL (list)
i++;
CHECK_LIST_END (list, list);
next prev parent reply other threads:[~2019-04-21 3:01 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-19 20:49 [RFC] Some new vector procedures (vector-{memq, apply, to-string, ...}) Alex Gramiak
2019-04-20 7:04 ` Eli Zaretskii
2019-04-20 16:50 ` Alex Gramiak
2019-04-20 17:16 ` Eli Zaretskii
2019-04-20 18:18 ` Alex Gramiak
2019-04-20 19:11 ` Eli Zaretskii
2019-04-20 19:54 ` Alan Mackenzie
2019-04-20 20:09 ` Óscar Fuentes
2019-04-20 22:54 ` Paul Eggert
2019-04-21 3:01 ` Alex Gramiak [this message]
2019-04-21 1:52 ` Alex Gramiak
2019-04-21 5:50 ` Eli Zaretskii
2019-04-21 4:05 ` Stefan Monnier
2019-04-21 20:34 ` Alex Gramiak
2019-04-21 21:01 ` Stefan Monnier
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