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faster m4_foreach
From: |
Eric Blake |
Subject: |
faster m4_foreach |
Date: |
Mon, 28 Jul 2008 17:54:46 +0000 (UTC) |
User-agent: |
Loom/3.14 (http://gmane.org/) |
While working with m4_set, I noticed a speed difference between:
m4_if([$#], [1], [], [$2[]$0([$1]_m4_shift2($@))])
and
m4_if([$#], [2], [], [$3[]$0([$1], m4_shift2($@))])
By injecting an ignored $2, we can avoid the m4_if embedded inside _m4_shift2,
and instead use the faster m4_shift2 in $@ recursion (m4_joinall was already
doing this, and I also used it in m4_set_add_all). I noticed as much as 5%
improvement on m4_foreach in isolation, although the improvement in real-life
testcases is rather minor (and there is no improvement to m4 1.4.x, which isn't
using $@ recursion in the first place).
With this patch, _m4_shift2, _m4_shift3, and _m4_cdr are now all unused within
autoconf. But even though they are undocumented, I won't delete them in case
other code is using them in spite of their undocumented nature.
From: Eric Blake <address@hidden>
Date: Mon, 28 Jul 2008 11:24:03 -0600
Subject: [PATCH] Avoid _m4_shiftn for m4 1.6 speedup.
* lib/m4sugar/m4sugar.m4 (m4_foreach, _m4_foreach, m4_map)
(_m4_map, m4_map_sep): Rewrite recursion to use one less m4_if.
* lib/m4sugar/foreach.m4 (_m4_map): Accomodate changed signature.
Signed-off-by: Eric Blake <address@hidden>
---
ChangeLog | 5 +++++
lib/m4sugar/foreach.m4 | 4 ++--
lib/m4sugar/m4sugar.m4 | 22 ++++++++++++----------
3 files changed, 19 insertions(+), 12 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 945891b..d46fd13 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
2008-07-28 Eric Blake <address@hidden>
+ Avoid _m4_shiftn for m4 1.6 speedup.
+ * lib/m4sugar/m4sugar.m4 (m4_foreach, _m4_foreach, m4_map)
+ (_m4_map, m4_map_sep): Rewrite recursion to use one less m4_if.
+ * lib/m4sugar/foreach.m4 (_m4_map): Accomodate changed signature.
+
Implement O(n) unique element set creation.
* lib/m4sugar/m4sugar.m4 (m4_set_add, m4_set_add_all)
(m4_set_contains, m4_set_contents, m4_set_delete)
diff --git a/lib/m4sugar/foreach.m4 b/lib/m4sugar/foreach.m4
index d6a9f72..0b1d05c 100644
--- a/lib/m4sugar/foreach.m4
+++ b/lib/m4sugar/foreach.m4
@@ -162,8 +162,8 @@ m4_define([m4_dquote_elt],
# m4_map/m4_map_sep only execute once; the speedup comes in fixing
# _m4_map. m4_foreach to the rescue.
m4_define([_m4_map],
-[m4_if([$#], [1], [],
- [m4_foreach([_m4_elt], [m4_shift($@)],
+[m4_if([$#], [2], [],
+ [m4_foreach([_m4_elt], [m4_shift2($@)],
[m4_apply([$1], m4_defn([_m4_elt]))])])])
# m4_join(SEP, ARG1, ARG2...)
diff --git a/lib/m4sugar/m4sugar.m4 b/lib/m4sugar/m4sugar.m4
index 9da7d57..293e38e 100644
--- a/lib/m4sugar/m4sugar.m4
+++ b/lib/m4sugar/m4sugar.m4
@@ -958,14 +958,15 @@ m4_if(m4_defn([$1]), [$2], [],
# as little as possible in _m4_foreach; each extra use requires that much
# more memory for expansion. So, rather than directly compare $2 against
# [] and use m4_car/m4_cdr for recursion, we instead unbox the list (which
-# requires swapping the argument order in the helper) and use _m4_shift3
-# to detect when recursion is complete.
+# requires swapping the argument order in the helper), insert an ignored
+# third argument, and use m4_shift3 to detect when recursion is complete.
m4_define([m4_foreach],
-[m4_pushdef([$1])_$0([$1], [$3]m4_if([$2], [], [], [, $2]))m4_popdef([$1])])
+[m4_if([$2], [], [],
+ [m4_pushdef([$1])_$0([$1], [$3], [], $2)m4_popdef([$1])])])
m4_define([_m4_foreach],
-[m4_if([$#], [2], [],
- [m4_define([$1], [$3])$2[]$0([$1], [$2]_m4_shift3($@))])])
+[m4_if([$#], [3], [],
+ [m4_define([$1], [$4])$2[]$0([$1], [$2], m4_shift3($@))])])
# m4_foreach_w(VARIABLE, LIST, EXPRESSION)
@@ -990,13 +991,14 @@ m4_define([m4_foreach_w],
#
# Since LIST may be quite large, we want to minimize how often it appears
# in the expansion. Rather than use m4_car/m4_cdr iteration, we unbox the
-# list, and use _m4_shift2 to detect the end of recursion.
+# list, ignore the second argument, and use m4_shift2 to detect the end of
+# recursion.
m4_define([m4_map],
[m4_if([$2], [], [],
- [_$0([$1], $2)])])
+ [_$0([$1], [], $2)])])
m4_define([_m4_map],
-[m4_if([$#], [1], [],
- [m4_apply([$1], [$2])$0([$1]_m4_shift2($@))])])
+[m4_if([$#], [2], [],
+ [m4_apply([$1], [$3])$0([$1], m4_shift2($@))])])
# m4_map_sep(MACRO, SEPARATOR, LIST)
@@ -1006,7 +1008,7 @@ m4_define([_m4_map],
# SEPARATOR is not further expanded.
m4_define([m4_map_sep],
[m4_if([$3], [], [],
- [m4_apply([$1], m4_car($3))_m4_map([[$2]$1]_m4_shift2(,$3))])])
+ [m4_apply([$1], m4_car($3))_m4_map([[$2]$1], $3)])])
## --------------------------- ##
--
1.5.6.4
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