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wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
It uses the same two-way algorithm used on strstr, strcasestr, and memmem. Different than strstr, neither the "shift table" optimization nor the self-adapting filtering check is used because it would result in a too-large shift table (and it also simplifies the implementation bit). Checked on x86_64-linux-gnu and aarch64-linux-gnu. Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
parent
4b717562c4
commit
cf11e74b0d
@ -59,6 +59,9 @@
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# undef weak_alias
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# define weak_alias(a, b)
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# define WCSSTR c_wcsstr
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# define __wmemcmp wmemcmp
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# define __wcsnlen wcsnlen
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# define __wcslen wcslen
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# include "wcsstr.c"
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# define C_IMPL WCSSTR
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#endif
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@ -217,6 +220,31 @@ check2 (void)
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}
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}
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static void
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check3 (void)
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{
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/* Check that a long periodic needle does not cause false positives. */
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{
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const CHAR input[] = L("F_BD_CE_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD"
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"_C3_88_20_EF_BF_BD_EF_BF_BD_EF_BF_BD"
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"_C3_A7_20_EF_BF_BD");
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const CHAR need[] = L("_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD");
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, input, need, NULL);
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}
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{
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const CHAR input[] = L("F_BD_CE_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD"
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"_C3_88_20_EF_BF_BD_EF_BF_BD_EF_BF_BD"
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"_C3_A7_20_EF_BF_BD_DA_B5_C2_A6_20"
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"_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD");
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const CHAR need[] = L("_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD");
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, input, need, (CHAR *) input + 115);
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}
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}
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#define N 1024
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static void
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@ -243,6 +271,148 @@ pr23637 (void)
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check_result (impl, h, n, exp_result);
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}
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static void
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pr23865 (void)
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{
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/* Check that a very long haystack is handled quickly if the needle is
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short and occurs near the beginning. */
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{
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size_t m = 1000000;
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const CHAR *needle =
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L("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
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"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
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CHAR *haystack = xmalloc ((m + 1) * sizeof (CHAR));
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MEMSET (haystack, L('A'), m);
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haystack[0] = L('B');
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haystack[m] = L('\0');
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, haystack, needle, haystack + 1);
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free (haystack);
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}
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/* Check that a very long needle is discarded quickly if the haystack is
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short. */
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{
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size_t m = 1000000;
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const CHAR *haystack =
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L("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
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"ABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABAB");
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CHAR *needle = xmalloc ((m + 1) * sizeof (CHAR));
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MEMSET (needle, L'A', m);
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needle[m] = L('\0');
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, haystack, needle, NULL);
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free (needle);
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}
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/* Check that the asymptotic worst-case complexity is not quadratic. */
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{
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size_t m = 1000000;
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CHAR *haystack = xmalloc ((2 * m + 2) * sizeof (CHAR));
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CHAR *needle = xmalloc ((m + 2) * sizeof (CHAR));
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MEMSET (haystack, L('A'), 2 * m);
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haystack[2 * m] = L('B');
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haystack[2 * m + 1] = L('\0');
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MEMSET (needle, L('A'), m);
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needle[m] = L('B');
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needle[m + 1] = L('\0');
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, haystack, needle, haystack + m);
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free (needle);
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free (haystack);
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}
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{
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/* Ensure that with a barely periodic "short" needle, STRSTR's
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search does not mistakenly skip just past the match point. */
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const CHAR *haystack =
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L("\n"
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"with_build_libsubdir\n"
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"with_local_prefix\n"
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"with_gxx_include_dir\n"
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"with_cpp_install_dir\n"
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"enable_generated_files_in_srcdir\n"
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"with_gnu_ld\n"
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"with_ld\n"
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"with_demangler_in_ld\n"
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"with_gnu_as\n"
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"with_as\n"
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"enable_largefile\n"
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"enable_werror_always\n"
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"enable_checking\n"
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"enable_coverage\n"
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"enable_gather_detailed_mem_stats\n"
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"enable_build_with_cxx\n"
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"with_stabs\n"
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"enable_multilib\n"
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"enable___cxa_atexit\n"
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"enable_decimal_float\n"
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"enable_fixed_point\n"
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"enable_threads\n"
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"enable_tls\n"
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"enable_objc_gc\n"
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"with_dwarf2\n"
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"enable_shared\n"
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"with_build_sysroot\n"
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"with_sysroot\n"
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"with_specs\n"
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"with_pkgversion\n"
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"with_bugurl\n"
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"enable_languages\n"
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"with_multilib_list\n");
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const CHAR *needle =
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L("\n"
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"with_gnu_ld\n");
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, haystack, needle, (CHAR*) haystack + 114);
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}
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{
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/* Same bug, shorter trigger. */
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const CHAR *haystack = L("..wi.d.");
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const CHAR *needle = L(".d.");
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, haystack, needle, (CHAR*) haystack + 4);
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}
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/* Test case from Yves Bastide.
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<https://www.openwall.com/lists/musl/2014/04/18/2> */
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{
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const CHAR *input = L("playing play play play always");
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const CHAR *needle = L("play play play");
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, input, needle, (CHAR*) input + 8);
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}
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/* Test long needles. */
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{
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size_t m = 1024;
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CHAR *haystack = xmalloc ((2 * m + 1) * sizeof (CHAR));
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CHAR *needle = xmalloc ((m + 1) * sizeof (CHAR));
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haystack[0] = L('x');
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MEMSET (haystack + 1, L(' '), m - 1);
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MEMSET (haystack + m, L('x'), m);
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haystack[2 * m] = L('\0');
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MEMSET (needle, L('x'), m);
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needle[m] = L('\0');
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FOR_EACH_IMPL (impl, 0)
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check_result (impl, haystack, needle, haystack + m);
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free (needle);
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free (haystack);
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}
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}
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static int
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test_main (void)
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{
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@ -250,7 +420,9 @@ test_main (void)
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check1 ();
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check2 ();
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check3 ();
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pr23637 ();
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pr23865 ();
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printf ("%23s", "");
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FOR_EACH_IMPL (impl, 0)
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312
wcsmbs/wcs-two-way.h
Normal file
312
wcsmbs/wcs-two-way.h
Normal file
@ -0,0 +1,312 @@
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/* Wide character substring search, using the Two-Way algorithm.
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Copyright (C) 2008-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* Before including this file, you need to include <string.h> (and
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<config.h> before that, if not part of libc), and define:
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AVAILABLE(h, h_l, j, n_l)
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A macro that returns nonzero if there are
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at least N_L characters left starting at H[J].
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H is 'wchar_t *', H_L, J, and N_L are 'size_t';
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H_L is an lvalue. For NUL-terminated searches,
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H_L can be modified each iteration to avoid
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having to compute the end of H up front.
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For case-insensitivity, you may optionally define:
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CMP_FUNC(p1, p2, l) A macro that returns 0 iff the first L
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characters of P1 and P2 are equal.
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CANON_ELEMENT(c) A macro that canonicalizes an element right after
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it has been fetched from one of the two strings.
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The argument is an 'wchar_t'; the result must
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be an 'wchar_t' as well.
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*/
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#include <limits.h>
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#include <stdint.h>
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#include <sys/param.h> /* Defines MAX. */
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/* We use the Two-Way string matching algorithm, which guarantees
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linear complexity with constant space.
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See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
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and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
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*/
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#ifndef CANON_ELEMENT
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# define CANON_ELEMENT(c) c
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#endif
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#ifndef CMP_FUNC
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# define CMP_FUNC __wmemcmp
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#endif
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/* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN.
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Return the index of the first character in the right half, and set
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*PERIOD to the global period of the right half.
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The global period of a string is the smallest index (possibly its
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length) at which all remaining bytes in the string are repetitions
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of the prefix (the last repetition may be a subset of the prefix).
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When NEEDLE is factored into two halves, a local period is the
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length of the smallest word that shares a suffix with the left half
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and shares a prefix with the right half. All factorizations of a
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non-empty NEEDLE have a local period of at least 1 and no greater
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than NEEDLE_LEN.
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A critical factorization has the property that the local period
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equals the global period. All strings have at least one critical
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factorization with the left half smaller than the global period.
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Given an ordered alphabet, a critical factorization can be computed
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in linear time, with 2 * NEEDLE_LEN comparisons, by computing the
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larger of two ordered maximal suffixes. The ordered maximal
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suffixes are determined by lexicographic comparison of
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periodicity. */
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static size_t
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critical_factorization (const wchar_t *needle, size_t needle_len,
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size_t *period)
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{
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/* Index of last character of left half, or SIZE_MAX. */
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size_t max_suffix, max_suffix_rev;
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size_t j; /* Index into NEEDLE for current candidate suffix. */
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size_t k; /* Offset into current period. */
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size_t p; /* Intermediate period. */
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wchar_t a, b; /* Current comparison bytes. */
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/* Special case NEEDLE_LEN of 1 or 2 (all callers already filtered
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out 0-length needles. */
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if (needle_len < 3)
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{
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*period = 1;
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return needle_len - 1;
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}
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/* Invariants:
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0 <= j < NEEDLE_LEN - 1
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-1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
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min(max_suffix, max_suffix_rev) < global period of NEEDLE
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1 <= p <= global period of NEEDLE
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p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j]
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1 <= k <= p
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*/
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/* Perform lexicographic search. */
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max_suffix = SIZE_MAX;
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j = 0;
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k = p = 1;
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while (j + k < needle_len)
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{
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a = CANON_ELEMENT (needle[j + k]);
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b = CANON_ELEMENT (needle[max_suffix + k]);
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if (a < b)
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{
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/* Suffix is smaller, period is entire prefix so far. */
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j += k;
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k = 1;
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p = j - max_suffix;
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}
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else if (a == b)
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{
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/* Advance through repetition of the current period. */
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if (k != p)
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++k;
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else
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{
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j += p;
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k = 1;
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}
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}
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else /* b < a */
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{
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/* Suffix is larger, start over from current location. */
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max_suffix = j++;
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k = p = 1;
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}
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}
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*period = p;
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/* Perform reverse lexicographic search. */
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max_suffix_rev = SIZE_MAX;
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j = 0;
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k = p = 1;
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while (j + k < needle_len)
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{
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a = CANON_ELEMENT (needle[j + k]);
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b = CANON_ELEMENT (needle[max_suffix_rev + k]);
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if (b < a)
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{
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/* Suffix is smaller, period is entire prefix so far. */
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j += k;
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k = 1;
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p = j - max_suffix_rev;
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}
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else if (a == b)
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{
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/* Advance through repetition of the current period. */
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if (k != p)
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++k;
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else
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{
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j += p;
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k = 1;
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}
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}
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else /* a < b */
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{
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/* Suffix is larger, start over from current location. */
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max_suffix_rev = j++;
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k = p = 1;
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}
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}
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/* Choose the shorter suffix. Return the first character of the right
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half, rather than the last character of the left half. */
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if (max_suffix_rev + 1 < max_suffix + 1)
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return max_suffix + 1;
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*period = p;
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return max_suffix_rev + 1;
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}
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/* Return the first location of non-empty NEEDLE within HAYSTACK, or
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NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK.
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If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
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most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching.
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If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
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HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching. */
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static inline wchar_t *
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two_way_short_needle (const wchar_t *haystack, size_t haystack_len,
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const wchar_t *needle, size_t needle_len)
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{
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size_t i; /* Index into current character of NEEDLE. */
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size_t j; /* Index into current window of HAYSTACK. */
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size_t period; /* The period of the right half of needle. */
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size_t suffix; /* The index of the right half of needle. */
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/* Factor the needle into two halves, such that the left half is
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smaller than the global period, and the right half is
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periodic (with a period as large as NEEDLE_LEN - suffix). */
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suffix = critical_factorization (needle, needle_len, &period);
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/* Perform the search. Each iteration compares the right half
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first. */
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if (CMP_FUNC (needle, needle + period, suffix) == 0)
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{
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/* Entire needle is periodic; a mismatch can only advance by the
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period, so use memory to avoid rescanning known occurrences
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of the period. */
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size_t memory = 0;
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j = 0;
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while (AVAILABLE (haystack, haystack_len, j, needle_len))
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{
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const wchar_t *pneedle;
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const wchar_t *phaystack;
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/* Scan for matches in right half. */
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i = MAX (suffix, memory);
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pneedle = &needle[i];
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phaystack = &haystack[i + j];
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while (i < needle_len && (CANON_ELEMENT (*pneedle++)
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== CANON_ELEMENT (*phaystack++)))
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++i;
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if (needle_len <= i)
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{
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/* Scan for matches in left half. */
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i = suffix - 1;
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pneedle = &needle[i];
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phaystack = &haystack[i + j];
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while (memory < i + 1 && (CANON_ELEMENT (*pneedle--)
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== CANON_ELEMENT (*phaystack--)))
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--i;
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if (i + 1 < memory + 1)
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return (wchar_t *) (haystack + j);
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/* No match, so remember how many repetitions of period
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on the right half were scanned. */
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j += period;
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memory = needle_len - period;
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}
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else
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{
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j += i - suffix + 1;
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memory = 0;
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}
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}
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}
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else
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{
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const wchar_t *phaystack;
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/* The comparison always starts from needle[suffix], so cache it
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and use an optimized first-character loop. */
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wchar_t needle_suffix = CANON_ELEMENT (needle[suffix]);
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/* The two halves of needle are distinct; no extra memory is
|
||||
required, and any mismatch results in a maximal shift. */
|
||||
period = MAX (suffix, needle_len - suffix) + 1;
|
||||
j = 0;
|
||||
while (AVAILABLE (haystack, haystack_len, j, needle_len))
|
||||
{
|
||||
wchar_t haystack_char;
|
||||
const wchar_t *pneedle;
|
||||
|
||||
phaystack = &haystack[suffix + j];
|
||||
|
||||
while (needle_suffix
|
||||
!= (haystack_char = CANON_ELEMENT (*phaystack++)))
|
||||
{
|
||||
++j;
|
||||
if (!AVAILABLE (haystack, haystack_len, j, needle_len))
|
||||
goto ret0;
|
||||
}
|
||||
|
||||
/* Scan for matches in right half. */
|
||||
i = suffix + 1;
|
||||
pneedle = &needle[i];
|
||||
while (i < needle_len)
|
||||
{
|
||||
if (CANON_ELEMENT (*pneedle++)
|
||||
!= (haystack_char = CANON_ELEMENT (*phaystack++)))
|
||||
break;
|
||||
++i;
|
||||
}
|
||||
if (needle_len <= i)
|
||||
{
|
||||
/* Scan for matches in left half. */
|
||||
i = suffix - 1;
|
||||
pneedle = &needle[i];
|
||||
phaystack = &haystack[i + j];
|
||||
while (i != SIZE_MAX)
|
||||
{
|
||||
if (CANON_ELEMENT (*pneedle--)
|
||||
!= (haystack_char = CANON_ELEMENT (*phaystack--)))
|
||||
break;
|
||||
--i;
|
||||
}
|
||||
if (i == SIZE_MAX)
|
||||
return (wchar_t *) (haystack + j);
|
||||
j += period;
|
||||
}
|
||||
else
|
||||
j += i - suffix + 1;
|
||||
}
|
||||
}
|
||||
ret0: __attribute__ ((unused))
|
||||
return NULL;
|
||||
}
|
||||
|
||||
#undef AVAILABLE
|
||||
#undef CANON_ELEMENT
|
||||
#undef CMP_FUNC
|
@ -1,4 +1,5 @@
|
||||
/* Copyright (C) 1995-2024 Free Software Foundation, Inc.
|
||||
/* Locate a substring in a wide-character string.
|
||||
Copyright (C) 1995-2024 Free Software Foundation, Inc.
|
||||
This file is part of the GNU C Library.
|
||||
|
||||
The GNU C Library is free software; you can redistribute it and/or
|
||||
@ -15,18 +16,14 @@
|
||||
License along with the GNU C Library; if not, see
|
||||
<https://www.gnu.org/licenses/>. */
|
||||
|
||||
/*
|
||||
* The original strstr() file contains the following comment:
|
||||
*
|
||||
* My personal strstr() implementation that beats most other algorithms.
|
||||
* Until someone tells me otherwise, I assume that this is the
|
||||
* fastest implementation of strstr() in C.
|
||||
* I deliberately chose not to comment it. You should have at least
|
||||
* as much fun trying to understand it, as I had to write it :-).
|
||||
*
|
||||
* Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
|
||||
|
||||
#include <wchar.h>
|
||||
#include <string.h>
|
||||
|
||||
#define AVAILABLE(h, h_l, j, n_l) \
|
||||
(((j) + (n_l) <= (h_l)) \
|
||||
|| ((h_l) += __wcsnlen ((void*)((h) + (h_l)), (n_l) + 128), \
|
||||
(j) + (n_l) <= (h_l)))
|
||||
#include "wcs-two-way.h"
|
||||
|
||||
#ifndef WCSSTR
|
||||
# define WCSSTR wcsstr
|
||||
@ -35,66 +32,20 @@
|
||||
wchar_t *
|
||||
WCSSTR (const wchar_t *haystack, const wchar_t *needle)
|
||||
{
|
||||
wchar_t b, c;
|
||||
/* Ensure haystack length is at least as long as needle length.
|
||||
Since a match may occur early on in a huge haystack, use strnlen
|
||||
and read ahead a few cachelines for improved performance. */
|
||||
size_t ne_len = __wcslen (needle);
|
||||
size_t hs_len = __wcsnlen (haystack, ne_len | 128);
|
||||
if (hs_len < ne_len)
|
||||
return NULL;
|
||||
|
||||
if ((b = *needle) != L'\0')
|
||||
{
|
||||
haystack--; /* possible ANSI violation */
|
||||
do
|
||||
if ((c = *++haystack) == L'\0')
|
||||
goto ret0;
|
||||
while (c != b);
|
||||
/* Check whether we have a match. This improves performance since we
|
||||
avoid initialization overheads. */
|
||||
if (__wmemcmp (haystack, needle, ne_len) == 0)
|
||||
return (wchar_t *) haystack;
|
||||
|
||||
if (!(c = *++needle))
|
||||
goto foundneedle;
|
||||
++needle;
|
||||
goto jin;
|
||||
|
||||
for (;;)
|
||||
{
|
||||
wchar_t a;
|
||||
const wchar_t *rhaystack, *rneedle;
|
||||
|
||||
do
|
||||
{
|
||||
if (!(a = *++haystack))
|
||||
goto ret0;
|
||||
if (a == b)
|
||||
break;
|
||||
if ((a = *++haystack) == L'\0')
|
||||
goto ret0;
|
||||
shloop: ;
|
||||
}
|
||||
while (a != b);
|
||||
|
||||
jin: if (!(a = *++haystack))
|
||||
goto ret0;
|
||||
|
||||
if (a != c)
|
||||
goto shloop;
|
||||
|
||||
if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
|
||||
do
|
||||
{
|
||||
if (a == L'\0')
|
||||
goto foundneedle;
|
||||
if (*++rhaystack != (a = *++needle))
|
||||
break;
|
||||
if (a == L'\0')
|
||||
goto foundneedle;
|
||||
}
|
||||
while (*++rhaystack == (a = *++needle));
|
||||
|
||||
needle = rneedle; /* took the register-poor approach */
|
||||
|
||||
if (a == L'\0')
|
||||
break;
|
||||
}
|
||||
}
|
||||
foundneedle:
|
||||
return (wchar_t*) haystack;
|
||||
ret0:
|
||||
return NULL;
|
||||
return two_way_short_needle (haystack, hs_len, needle, ne_len);
|
||||
}
|
||||
/* This alias is for backward compatibility with drafts of the ISO C
|
||||
standard. Unfortunately the Unix(TM) standard requires this name. */
|
||||
|
Loading…
Reference in New Issue
Block a user