Subject: bug#16232: [PATCH] grep: make --ignore-case (-i) faster (sometimes 10x) in multibyte locales

From: Jim Meyering <[email-masked]>
Date: Tue, 7 Jan 2014 19:56:21 -0800

On Mon, Dec 23, 2013 at 3:54 PM, Jim Meyering <[email-masked]> wrote:
...
> Thanks for dotting those 'i's.  While there is no risk of buffer
> overrun, there would definitely be a problem with the tr_TR locale.
> I will resolve it by removing the isascii check and performing
> multibyte case conversion to form each [cC] pair.  Of course,
> that will mean removing the "4 * byte-length-of-search-string"
> buffer size limitation.
>
> I will also add tests based on your examples.

Here is the improved patch.
From 2d2273f30707bdc89673f87906f597d15466ce22 Mon Sep 17 00:00:00 2001
From: Jim Meyering <[email-masked]>
Date: Sun, 24 Nov 2013 18:49:31 -0800
Subject: [PATCH] grep: make --ignore-case (-i) faster (sometimes 10x) in
 multibyte locales

These days, nearly everyone uses a multibyte locale, and grep is often
used with the --ignore-case (-i) option, but that option imposes a very
high cost in order to handle some unusual cases in just a few multibyte
locales.  This change gets most of the performance of using LC_ALL=C
without eliminating the ability to search for multibyte strings.

With the following example, I see an 11x speed-up with a 2.3GHz i7:
Generate a 10M-line file, with each line consisting of 40 'j's:

    yes jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj | head -10000000 > k

Time searching it for the simple/noexistent string "foobar",
first with this patch (best-of-5 trials):

    LC_ALL=en_US.UTF-8 env time src/grep -i foobar k
        1.10 real         1.03 user         0.07 sys

Back out that commit (temporarily), recompile, and rerun the experiment:

    git log -1 -p|patch -R -p1; make
    LC_ALL=en_US.UTF-8 env time src/grep -i foobar k
        12.50 real        12.41 user         0.08 sys

The trick is to realize that for some search strings, it is easy
to convert to an equivalent one that is handled much more efficiently.
E.g., convert this command:

  grep -i foobar k

to this:

  grep '[fF][oO][oO][bB][aA][rR]' k

That allows the matcher to search in buffer mode, rather than having to
extract/case-convert/search each line separately.  Currently, we perform
this conversion only when search strings contain neither '\' nor '['.
See the comments for more detail.

* src/main.c (trivial_case_ignore): New function.
(main): When possible, transform the regexp so we can drop the -i.
* tests/turkish-eyes: New file.
* tests/Makefile.am (TESTS): Use it.
---
 src/main.c         | 111 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 tests/Makefile.am  |   1 +
 tests/turkish-eyes |  44 +++++++++++++++++++++
 3 files changed, 155 insertions(+), 1 deletion(-)
 create mode 100755 tests/turkish-eyes

diff --git a/src/main.c b/src/main.c
index 44090be..bfd0982 100644
--- a/src/main.c
+++ b/src/main.c
@@ -27,6 +27,7 @@
 #include <fcntl.h>
 #include <inttypes.h>
 #include <stdio.h>
+#include <assert.h>
 #include "system.h"

 #include "argmatch.h"
@@ -1644,13 +1645,14 @@ if any error occurs and -q is not given, the exit status is 2.\n"));
   exit (status);
 }

+static char const *matcher;
+
 /* If M is NULL, initialize the matcher to the default.  Otherwise set the
    matcher to M if available.  Exit in case of conflicts or if M is not
    available.  */
 static void
 setmatcher (char const *m)
 {
-  static char const *matcher;
   unsigned int i;

   if (!m)
@@ -1865,6 +1867,84 @@ parse_grep_colors (void)
       return;
 }

+#define MBRTOWC(pwc, s, n, ps) \
+  (MB_CUR_MAX == 1 ? \
+   (*(pwc) = btowc (*(unsigned char *) (s)), 1) : \
+   mbrtowc ((pwc), (s), (n), (ps)))
+
+#define WCRTOMB(s, wc, ps) \
+  (MB_CUR_MAX == 1 ? \
+   (*(s) = wctob ((wint_t) (wc)), 1) : \
+   wcrtomb ((s), (wc), (ps)))
+
+/* If the newline-separated regular expressions, KEYS (with length, LEN
+   and no trailing NUL byte), are amenable to transformation into
+   otherwise equivalent case-ignoring ones, perform the transformation,
+   put the result into malloc'd memory, *NEW_KEYS with length *NEW_LEN,
+   and return true.  Otherwise, return false.  */
+static bool
+trivial_case_ignore (size_t len, char const *keys,
+                     size_t *new_len, char **new_keys)
+{
+  /* FIXME: consider removing the following restriction:
+     Reject if KEYS contain ASCII '\\' or '['.  */
+  if (memchr (keys, '\\', len) || memchr (keys, '[', len))
+    return false;
+
+  /* Worst case is that each byte B of KEYS is ASCII alphabetic and each
+     other_case(B) character, C, occupies MB_CUR_MAX bytes, so each B
+     maps to [BC], which requires MB_CUR_MAX + 3 bytes.   */
+  *new_keys = xnmalloc (MB_CUR_MAX + 3, len + 1);
+  char *p = *new_keys;
+
+  mbstate_t mb_state;
+  memset (&mb_state, 0, sizeof mb_state);
+  while (len)
+    {
+      wchar_t wc;
+      int n = MBRTOWC (&wc, keys, len, &mb_state);
+
+      /* For an invalid, incomplete or L'\0', skip this optimization.  */
+      if (n <= 0)
+        {
+        skip_case_ignore_optimization:
+          free (*new_keys);
+          return false;
+        }
+
+      char const *orig = keys;
+      keys += n;
+      len -= n;
+
+      if (!iswalpha (wc))
+        {
+          memcpy (p, orig, n);
+          p += n;
+        }
+      else
+        {
+          *p++ = '[';
+          memcpy (p, orig, n);
+          p += n;
+
+          wchar_t wc2 = iswupper (wc) ? towlower (wc) : towupper (wc);
+          char buf[MB_CUR_MAX];
+          int n2 = WCRTOMB (buf, wc2, &mb_state);
+          if (n2 <= 0)
+            goto skip_case_ignore_optimization;
+          assert (n2 <= MB_CUR_MAX);
+          memcpy (p, buf, n2);
+          p += n2;
+
+          *p++ = ']';
+        }
+    }
+
+  *new_len = p - *new_keys;
+
+  return true;
+}
+
 int
 main (int argc, char **argv)
 {
@@ -2263,6 +2343,35 @@ main (int argc, char **argv)
   else
     usage (EXIT_TROUBLE);

+  /* As currently implemented, case-insensitive matching is expensive in
+     multi-byte locales because of a few outlier locales in which some
+     characters change size when converted to upper or lower case.  To
+     accommodate those, we revert to searching the input one line at a
+     time, rather than using the much more efficient buffer search.
+     However, if we have a regular expression, /foo/i, we can convert
+     it to an equivalent case-insensitive /[fF][oO][oO]/, and thus
+     avoid the expensive read-and-process-a-line-at-a-time requirement.
+     Optimize-away the "-i" option, when possible, converting each
+     candidate alpha, C, in the regexp to [Cc].  */
+  if (match_icase)
+    {
+      size_t new_keycc;
+      char *new_keys;
+      /* It is not possible with -F, not useful with -P (pcre) and there is no
+         point when there is no regexp.  It also depends on which constructs
+         appear in the regexp.  See trivial_case_ignore for those details.  */
+      if (keycc
+          && ! (matcher
+                && (STREQ (matcher, "fgrep") || STREQ (matcher, "pcre")))
+          && trivial_case_ignore (keycc, keys, &new_keycc, &new_keys))
+        {
+          match_icase = 0;
+          free (keys);
+          keys = new_keys;
+          keycc = new_keycc;
+        }
+    }
+
   compile (keys, keycc);
   free (keys);

diff --git a/tests/Makefile.am b/tests/Makefile.am
index f4580b5..a37a814 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -94,6 +94,7 @@ TESTS =						\
   status					\
   surrogate-pair				\
   symlink					\
+  turkish-eyes					\
   turkish-I					\
   turkish-I-without-dot				\
   warn-char-classes				\
diff --git a/tests/turkish-eyes b/tests/turkish-eyes
new file mode 100755
index 0000000..323eb35
--- /dev/null
+++ b/tests/turkish-eyes
@@ -0,0 +1,44 @@
+#!/bin/sh
+# Ensure that case-insensitive matching works with all Turkish i's
+
+# Copyright (C) 2014 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+
+require_compiled_in_MB_support
+
+fail=0
+
+L=tr_TR.UTF-8
+
+# Check for a broken tr_TR.UTF-8 locale definition.
+# In this locale, 'i' is not a lower-case 'I'.
+echo I | LC_ALL=$L grep -i i > /dev/null \
+    && skip_ "your $L locale appears to be broken"
+
+# Ensure that this matches:
+# printf 'I:İ ı:i\n'|LC_ALL=tr_TR.utf8 grep -i 'ı:i I:İ'
+I=$(printf '\304\260') # capital I with dot
+i=$(printf '\304\261') # lowercase dotless i
+
+data=$(      printf "I:$I $i:i")
+search_str=$(printf "$i:i I:$I")
+printf "$data\n" > in || framework_failure_
+
+LC_ALL=$L grep -i "^$search_str\$" in > out || fail=1
+compare out in || fail=1
+
+Exit $fail
-- 
1.8.5.2.229.g4448466