Thanks to Jim and for the new release. Let's just start with, for next
release I want to add further improvement to it.
In dfaexec, DFA state is always 0 until have found potential match. So
we can improve matching there by continuing to use the transition table
without replacing it.
I tested the patch, and got about 3x speed-up.
$ yes j | head -10000000 >k
$ env LC_ALL=C time -p src/grep '\(a\|b\)' k
Before: real 1.12 user 1.06 sys 0.04
After : real 0.39 user 0.34 sys 0.04
I also tested for non-utf8 multibyte locale.
$ env LC_ALL=ja_JP.eucJP time -p src/grep '\(a\|b\)' k
Before: real 1.41 user 1.35 sys 0.05
After : real 0.38 user 0.32 sys 0.06
By the way, below on grep 2.18 (non-patch). (^_^)
$ env LANG=ja_JP.eucJP time -p src/grep '\(a\|b\)' k
real 12.00 user 11.86 sys 0.13
From 6918bc2493ff7ae21c50a3b4d358ae3028374a09 Mon Sep 17 00:00:00 2001
From: Norihiro Tanaka <nori...@kcn.ne.jp>
Date: Tue, 13 May 2014 10:30:21 +0900
Subject: [PATCH] dfa: speed-up at initial state
DFA state is always 0 until have found potential match. So we improve
matching there by continuing to use the transition table.
* src/dfa.c (skip_remains_mb): New function.
(dfaexec): Speed-up at initial state.
---
src/dfa.c | 54 +++++++++++++++++++++++++++++++++++-------------------
1 file changed, 35 insertions(+), 19 deletions(-)
diff --git a/src/dfa.c b/src/dfa.c
index 8ff29d0..1d73105 100644
--- a/src/dfa.c
+++ b/src/dfa.c
@@ -3250,6 +3250,24 @@ transit_state (struct dfa *d, state_num s, unsigned char
const **pp,
return s1;
}
+/* The initial state may encounter a byte which is not a single byte character
+ nor the first byte of a multibyte character. But it is incorrect for the
+ initial state to accept such a byte. For example, in Shift JIS the regular
+ expression "\\" accepts the codepoint 0x5c, but should not accept the second
+ byte of the codepoint 0x815c. Then the initial state must skip the bytes
+ that are not a single byte character nor the first byte of a multibyte
+ character. */
+static unsigned char const *
+skip_remains_mb (struct dfa *d, unsigned char const *p,
+ unsigned char const *mbp, char const *end)
+{
+ wint_t wc;
+ while (mbp < p)
+ mbp += mbs_to_wchar (&wc, (char const *) mbp,
+ end - (char const *) mbp, d);
+ return mbp;
+}
+
/* Search through a buffer looking for a match to the given struct dfa.
Find the first occurrence of a string matching the regexp in the
buffer, and the shortest possible version thereof. Return a pointer to
@@ -3303,27 +3321,18 @@ dfaexec (struct dfa *d, char const *begin, char *end,
if (s == 0)
{
- /* The initial state may encounter a byte which is not
- a single byte character nor the first byte of a
- multibyte character. But it is incorrect for the
- initial state to accept such a byte. For example,
- in Shift JIS the regular expression "\\" accepts
- the codepoint 0x5c, but should not accept the second
- byte of the codepoint 0x815c. Then the initial
- state must skip the bytes that are not a single
- byte character nor the first byte of a multibyte
- character. */
- wint_t wc;
- while (mbp < p)
- mbp += mbs_to_wchar (&wc, (char const *) mbp,
- end - (char const *) mbp, d);
- p = mbp;
-
- if ((char *) p > end)
+ if (d->states[s].mbps.nelem == 0)
{
- p = NULL;
- goto done;
+ do
+ {
+ while (t[*p] == 0)
+ p++;
+ p = mbp = skip_remains_mb (d, p, mbp, end);
+ }
+ while (t[*p] == 0);
}
+ else
+ p = mbp = skip_remains_mb (d, p, mbp, end);
}
if (d->states[s].mbps.nelem == 0)
@@ -3351,6 +3360,13 @@ dfaexec (struct dfa *d, char const *begin, char *end,
}
else
{
+ if (s == 0 && (t = trans[s]) != NULL)
+ {
+ while (t[*p] == 0)
+ p++;
+ s = t[*p++];
+ }
+
while ((t = trans[s]) != NULL)
{
s1 = t[*p++];
--
1.9.3
