* [PATCH 1/3] string: Remove c_strstr from test-strstr
2024-02-19 20:44 [PATCH 0/3] Improve wcsstr Adhemerval Zanella
@ 2024-02-19 20:45 ` Adhemerval Zanella
2024-02-19 20:45 ` [PATCH 2/3] wcsmbs: Add test-wcsstr Adhemerval Zanella
2024-02-19 20:45 ` [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865) Adhemerval Zanella
2 siblings, 0 replies; 10+ messages in thread
From: Adhemerval Zanella @ 2024-02-19 20:45 UTC (permalink / raw)
To: libc-alpha
There is no much point is checking the generic code if this is not
really used by libc.
---
string/test-strstr.c | 6 ------
1 file changed, 6 deletions(-)
diff --git a/string/test-strstr.c b/string/test-strstr.c
index 4115f7d2fd..05d0b7c98c 100644
--- a/string/test-strstr.c
+++ b/string/test-strstr.c
@@ -21,11 +21,6 @@
#include "test-string.h"
-#define STRSTR c_strstr
-#define libc_hidden_builtin_def(arg) /* nothing */
-#define __strnlen strnlen
-#include "strstr.c"
-
/* Naive implementation to verify results. */
static char *
simple_strstr (const char *s1, const char *s2)
@@ -52,7 +47,6 @@ simple_strstr (const char *s1, const char *s2)
typedef char *(*proto_t) (const char *, const char *);
-IMPL (c_strstr, 0)
IMPL (strstr, 1)
--
2.34.1
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 2/3] wcsmbs: Add test-wcsstr
2024-02-19 20:44 [PATCH 0/3] Improve wcsstr Adhemerval Zanella
2024-02-19 20:45 ` [PATCH 1/3] string: Remove c_strstr from test-strstr Adhemerval Zanella
@ 2024-02-19 20:45 ` Adhemerval Zanella
2024-02-19 20:45 ` [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865) Adhemerval Zanella
2 siblings, 0 replies; 10+ messages in thread
From: Adhemerval Zanella @ 2024-02-19 20:45 UTC (permalink / raw)
To: libc-alpha
Parametrize test-strstr.c so it can be used to check wcsstr.
Checked on x86_64-linux-gnu and aarch64-linux-gnu.
---
string/test-strstr.c | 125 +++++++++++++++++++++++++++----------------
wcsmbs/Makefile | 1 +
wcsmbs/test-wcsstr.c | 20 +++++++
3 files changed, 100 insertions(+), 46 deletions(-)
create mode 100644 wcsmbs/test-wcsstr.c
diff --git a/string/test-strstr.c b/string/test-strstr.c
index 05d0b7c98c..3d7858e6be 100644
--- a/string/test-strstr.c
+++ b/string/test-strstr.c
@@ -17,16 +17,44 @@
<https://www.gnu.org/licenses/>. */
#define TEST_MAIN
-#define TEST_NAME "strstr"
-#include "test-string.h"
+#ifndef WIDE
+# define TEST_NAME "strstr"
+#else
+# define TEST_NAME "wcsstr"
+#endif
+
+#ifndef WIDE
+# define CHAR char
+# define STRLEN strlen
+# define STRSTR strstr
+# define STRCPY strcpy
+# define MEMCPY memcpy
+# define MEMSET memset
+# define MEMPCPY mempcpy
+# define L(s) s
+#else
+# include <wchar.h>
+# define CHAR wchar_t
+# define STRLEN wcslen
+# define STRCPY wcscpy
+# define STRSTR wcsstr
+# define MEMCPY wmemcpy
+# define MEMSET wmemset
+# define MEMPCPY wmempcpy
+# define L(s) L ## s
+/* The test requires up to 8191 charateres, so allocate at least 32Kb
+ (considering 4kb page size). */
+# define BUF1PAGES 4
+#endif
+#include "test-string.h"
/* Naive implementation to verify results. */
-static char *
-simple_strstr (const char *s1, const char *s2)
+static CHAR *
+simple_strstr (const CHAR *s1, const CHAR *s2)
{
- ssize_t s1len = strlen (s1);
- ssize_t s2len = strlen (s2);
+ ssize_t s1len = STRLEN (s1);
+ ssize_t s2len = STRLEN (s2);
if (s2len > s1len)
return NULL;
@@ -38,28 +66,27 @@ simple_strstr (const char *s1, const char *s2)
if (s1[i + j] != s2[j])
break;
if (j == s2len)
- return (char *) s1 + i;
+ return (CHAR *) s1 + i;
}
return NULL;
}
-typedef char *(*proto_t) (const char *, const char *);
+typedef CHAR *(*proto_t) (const CHAR *, const CHAR *);
-IMPL (strstr, 1)
+IMPL (STRSTR, 1)
static int
-check_result (impl_t *impl, const char *s1, const char *s2,
- char *exp_result)
+check_result (impl_t *impl, const CHAR *s1, const CHAR *s2,
+ CHAR *exp_result)
{
- char *result = CALL (impl, s1, s2);
+ CHAR *result = CALL (impl, s1, s2);
if (result != exp_result)
{
- error (0, 0, "Wrong result in function %s %s %s", impl->name,
- (result == NULL) ? "(null)" : result,
- (exp_result == NULL) ? "(null)" : exp_result);
+ error (0, 0, "Wrong result in function %p %p %p", impl->name,
+ result, exp_result);
ret = 1;
return -1;
}
@@ -68,7 +95,7 @@ check_result (impl_t *impl, const char *s1, const char *s2,
}
static void
-do_one_test (impl_t *impl, const char *s1, const char *s2, char *exp_result)
+do_one_test (impl_t *impl, const CHAR *s1, const CHAR *s2, CHAR *exp_result)
{
if (check_result (impl, s1, s2, exp_result) < 0)
return;
@@ -79,49 +106,52 @@ static void
do_test (size_t align1, size_t align2, size_t len1, size_t len2,
int fail)
{
- char *s1 = (char *) (buf1 + align1);
- char *s2 = (char *) (buf2 + align2);
+ align1 = align1 * sizeof (CHAR);
+ align2 = align2 * sizeof (CHAR);
- static const char d[] = "1234567890abcdef";
-#define dl (sizeof (d) - 1)
- char *ss2 = s2;
+ CHAR *s1 = (CHAR *) (buf1 + align1);
+ CHAR *s2 = (CHAR *) (buf2 + align2);
+
+ static const CHAR d[] = L("1234567890abcdef");
+ const size_t dl = STRLEN (d);
+ CHAR *ss2 = s2;
for (size_t l = len2; l > 0; l = l > dl ? l - dl : 0)
{
size_t t = l > dl ? dl : l;
- ss2 = mempcpy (ss2, d, t);
+ ss2 = MEMPCPY (ss2, d, t);
}
s2[len2] = '\0';
if (fail)
{
- char *ss1 = s1;
+ CHAR *ss1 = s1;
for (size_t l = len1; l > 0; l = l > dl ? l - dl : 0)
{
size_t t = l > dl ? dl : l;
- memcpy (ss1, d, t);
+ MEMCPY (ss1, d, t);
++ss1[len2 > 7 ? 7 : len2 - 1];
ss1 += t;
}
}
else
{
- memset (s1, '0', len1);
- memcpy (s1 + len1 - len2, s2, len2);
+ MEMSET (s1, '0', len1);
+ MEMCPY (s1 + len1 - len2, s2, len2);
}
s1[len1] = '\0';
FOR_EACH_IMPL (impl, 0)
do_one_test (impl, s1, s2, fail ? NULL : s1 + len1 - len2);
-
}
static void
+__attribute_used__
check1 (void)
{
- const char s1[] =
- "F_BD_CE_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_C3_88_20_EF_BF_BD_EF_BF_BD_EF_BF_BD_C3_A7_20_EF_BF_BD";
- const char s2[] = "_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD";
- char *exp_result;
+ const CHAR s1[] =
+ L("F_BD_CE_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_C3_88_20_EF_BF_BD_EF_BF_BD_EF_BF_BD_C3_A7_20_EF_BF_BD");
+ const CHAR s2[] = L("_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD");
+ CHAR *exp_result;
exp_result = simple_strstr (s1, s2);
FOR_EACH_IMPL (impl, 0)
@@ -129,32 +159,34 @@ check1 (void)
}
static void
+__attribute_used__
check2 (void)
{
- const char s1_stack[] = ", enable_static, \0, enable_shared, ";
+ const CHAR s1_stack[] = L(", enable_static, \0, enable_shared, ");
const size_t s1_byte_count = 18;
- const char *s2_stack = &(s1_stack[s1_byte_count]);
- const size_t s2_byte_count = 18;
- char *exp_result;
+ const size_t s1_byte_len = 18 * sizeof (CHAR);
+ const CHAR *s2_stack = &(s1_stack[s1_byte_count]);
+ const size_t s2_byte_len = 18 * sizeof (CHAR);;
+ CHAR *exp_result;
const size_t page_size_real = getpagesize ();
/* Haystack at end of page. The following page is protected. */
- char *s1_page_end = (void *) buf1 + page_size - s1_byte_count;
- strcpy (s1_page_end, s1_stack);
+ CHAR *s1_page_end = (void *) buf1 + page_size - s1_byte_len;
+ STRCPY (s1_page_end, s1_stack);
/* Haystack which crosses a page boundary.
Note: page_size is at least 2 * getpagesize. See test_init. */
- char *s1_page_cross = (void *) buf1 + page_size_real - 8;
- strcpy (s1_page_cross, s1_stack);
+ CHAR *s1_page_cross = (void *) buf1 + page_size_real - 8;
+ STRCPY (s1_page_cross, s1_stack);
/* Needle at end of page. The following page is protected. */
- char *s2_page_end = (void *) buf2 + page_size - s2_byte_count;
- strcpy (s2_page_end, s2_stack);
+ CHAR *s2_page_end = (void *) buf2 + page_size - s2_byte_len;
+ STRCPY (s2_page_end, s2_stack);
/* Needle which crosses a page boundary.
Note: page_size is at least 2 * getpagesize. See test_init. */
- char *s2_page_cross = (void *) buf2 + page_size_real - 8;
- strcpy (s2_page_cross, s2_stack);
+ CHAR *s2_page_cross = (void *) buf2 + page_size_real - 8;
+ STRCPY (s2_page_cross, s2_stack);
exp_result = simple_strstr (s1_stack, s2_stack);
FOR_EACH_IMPL (impl, 0)
@@ -176,10 +208,11 @@ check2 (void)
#define N 1024
static void
+__attribute_used__
pr23637 (void)
{
- char *h = (char*) buf1;
- char *n = (char*) buf2;
+ CHAR *h = (CHAR*) buf1;
+ CHAR *n = (CHAR*) buf2;
for (int i = 0; i < N; i++)
{
@@ -194,7 +227,7 @@ pr23637 (void)
/* Ensure we don't match at the first 'x'. */
h[0] = 'x';
- char *exp_result = simple_strstr (h, n);
+ CHAR *exp_result = simple_strstr (h, n);
FOR_EACH_IMPL (impl, 0)
check_result (impl, h, n, exp_result);
}
diff --git a/wcsmbs/Makefile b/wcsmbs/Makefile
index f3333c6a4b..1cddd8cc6d 100644
--- a/wcsmbs/Makefile
+++ b/wcsmbs/Makefile
@@ -163,6 +163,7 @@ tests := \
test-wcspbrk \
test-wcsrchr \
test-wcsspn \
+ test-wcsstr \
test-wmemchr \
test-wmemcmp \
test-wmemset \
diff --git a/wcsmbs/test-wcsstr.c b/wcsmbs/test-wcsstr.c
new file mode 100644
index 0000000000..cb9b2f51c0
--- /dev/null
+++ b/wcsmbs/test-wcsstr.c
@@ -0,0 +1,20 @@
+/* Test wcsstr function.
+ Copyright (C) 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
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#define WIDE 1
+#include "../string/test-strstr.c"
--
2.34.1
^ permalink raw reply [flat|nested] 10+ messages in thread* [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-19 20:44 [PATCH 0/3] Improve wcsstr Adhemerval Zanella
2024-02-19 20:45 ` [PATCH 1/3] string: Remove c_strstr from test-strstr Adhemerval Zanella
2024-02-19 20:45 ` [PATCH 2/3] wcsmbs: Add test-wcsstr Adhemerval Zanella
@ 2024-02-19 20:45 ` Adhemerval Zanella
2024-02-20 0:15 ` Noah Goldstein
2 siblings, 1 reply; 10+ messages in thread
From: Adhemerval Zanella @ 2024-02-19 20:45 UTC (permalink / raw)
To: libc-alpha
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.
---
wcsmbs/wcs-two-way.h | 312 +++++++++++++++++++++++++++++++++++++++++++
wcsmbs/wcsstr.c | 104 +++++----------
2 files changed, 344 insertions(+), 72 deletions(-)
create mode 100644 wcsmbs/wcs-two-way.h
diff --git a/wcsmbs/wcs-two-way.h b/wcsmbs/wcs-two-way.h
new file mode 100644
index 0000000000..2dcee7fc1a
--- /dev/null
+++ b/wcsmbs/wcs-two-way.h
@@ -0,0 +1,312 @@
+/* Byte-wise substring search, using the Two-Way algorithm.
+ Copyright (C) 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
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* Before including this file, you need to include <string.h> (and
+ <config.h> before that, if not part of libc), and define:
+ AVAILABLE(h, h_l, j, n_l)
+ A macro that returns nonzero if there are
+ at least N_L characters left starting at H[J].
+ H is 'wchar_t *', H_L, J, and N_L are 'size_t';
+ H_L is an lvalue. For NUL-terminated searches,
+ H_L can be modified each iteration to avoid
+ having to compute the end of H up front.
+
+ For case-insensitivity, you may optionally define:
+ CMP_FUNC(p1, p2, l) A macro that returns 0 iff the first L
+ characters of P1 and P2 are equal.
+ CANON_ELEMENT(c) A macro that canonicalizes an element right after
+ it has been fetched from one of the two strings.
+ The argument is an 'wchar_t'; the result must
+ be an 'wchar_t' as well.
+*/
+
+#include <limits.h>
+#include <stdint.h>
+#include <sys/param.h> /* Defines MAX. */
+
+/* We use the Two-Way string matching algorithm, which guarantees
+ linear complexity with constant space.
+
+ See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
+ and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
+*/
+
+#ifndef CANON_ELEMENT
+# define CANON_ELEMENT(c) c
+#endif
+#ifndef CMP_FUNC
+# define CMP_FUNC __wmemcmp
+#endif
+
+/* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN.
+ Return the index of the first character in the right half, and set
+ *PERIOD to the global period of the right half.
+
+ The global period of a string is the smallest index (possibly its
+ length) at which all remaining bytes in the string are repetitions
+ of the prefix (the last repetition may be a subset of the prefix).
+
+ When NEEDLE is factored into two halves, a local period is the
+ length of the smallest word that shares a suffix with the left half
+ and shares a prefix with the right half. All factorizations of a
+ non-empty NEEDLE have a local period of at least 1 and no greater
+ than NEEDLE_LEN.
+
+ A critical factorization has the property that the local period
+ equals the global period. All strings have at least one critical
+ factorization with the left half smaller than the global period.
+
+ Given an ordered alphabet, a critical factorization can be computed
+ in linear time, with 2 * NEEDLE_LEN comparisons, by computing the
+ larger of two ordered maximal suffixes. The ordered maximal
+ suffixes are determined by lexicographic comparison of
+ periodicity. */
+static size_t
+critical_factorization (const wchar_t *needle, size_t needle_len,
+ size_t *period)
+{
+ /* Index of last character of left half, or SIZE_MAX. */
+ size_t max_suffix, max_suffix_rev;
+ size_t j; /* Index into NEEDLE for current candidate suffix. */
+ size_t k; /* Offset into current period. */
+ size_t p; /* Intermediate period. */
+ wchar_t a, b; /* Current comparison bytes. */
+
+ /* Special case NEEDLE_LEN of 1 or 2 (all callers already filtered
+ out 0-length needles. */
+ if (needle_len < 3)
+ {
+ *period = 1;
+ return needle_len - 1;
+ }
+
+ /* Invariants:
+ 0 <= j < NEEDLE_LEN - 1
+ -1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
+ min(max_suffix, max_suffix_rev) < global period of NEEDLE
+ 1 <= p <= global period of NEEDLE
+ p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j]
+ 1 <= k <= p
+ */
+
+ /* Perform lexicographic search. */
+ max_suffix = SIZE_MAX;
+ j = 0;
+ k = p = 1;
+ while (j + k < needle_len)
+ {
+ a = CANON_ELEMENT (needle[j + k]);
+ b = CANON_ELEMENT (needle[max_suffix + k]);
+ if (a < b)
+ {
+ /* Suffix is smaller, period is entire prefix so far. */
+ j += k;
+ k = 1;
+ p = j - max_suffix;
+ }
+ else if (a == b)
+ {
+ /* Advance through repetition of the current period. */
+ if (k != p)
+ ++k;
+ else
+ {
+ j += p;
+ k = 1;
+ }
+ }
+ else /* b < a */
+ {
+ /* Suffix is larger, start over from current location. */
+ max_suffix = j++;
+ k = p = 1;
+ }
+ }
+ *period = p;
+
+ /* Perform reverse lexicographic search. */
+ max_suffix_rev = SIZE_MAX;
+ j = 0;
+ k = p = 1;
+ while (j + k < needle_len)
+ {
+ a = CANON_ELEMENT (needle[j + k]);
+ b = CANON_ELEMENT (needle[max_suffix_rev + k]);
+ if (b < a)
+ {
+ /* Suffix is smaller, period is entire prefix so far. */
+ j += k;
+ k = 1;
+ p = j - max_suffix_rev;
+ }
+ else if (a == b)
+ {
+ /* Advance through repetition of the current period. */
+ if (k != p)
+ ++k;
+ else
+ {
+ j += p;
+ k = 1;
+ }
+ }
+ else /* a < b */
+ {
+ /* Suffix is larger, start over from current location. */
+ max_suffix_rev = j++;
+ k = p = 1;
+ }
+ }
+
+ /* Choose the shorted suffix. Return the first character of the right
+ half, rather than the last character of the left half. */
+ if (max_suffix_rev + 1 < max_suffix + 1)
+ return max_suffix + 1;
+ *period = p;
+ return max_suffix_rev + 1;
+}
+
+/* Return the first location of non-empty NEEDLE within HAYSTACK, or
+ NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK.
+
+ If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
+ most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching.
+ If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
+ HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching. */
+static inline wchar_t *
+two_way_short_needle (const wchar_t *haystack, size_t haystack_len,
+ const wchar_t *needle, size_t needle_len)
+{
+ size_t i; /* Index into current character of NEEDLE. */
+ size_t j; /* Index into current window of HAYSTACK. */
+ size_t period; /* The period of the right half of needle. */
+ size_t suffix; /* The index of the right half of needle. */
+
+ /* Factor the needle into two halves, such that the left half is
+ smaller than the global period, and the right half is
+ periodic (with a period as large as NEEDLE_LEN - suffix). */
+ suffix = critical_factorization (needle, needle_len, &period);
+
+ /* Perform the search. Each iteration compares the right half
+ first. */
+ if (CMP_FUNC (needle, needle + period, suffix) == 0)
+ {
+ /* Entire needle is periodic; a mismatch can only advance by the
+ period, so use memory to avoid rescanning known occurrences
+ of the period. */
+ size_t memory = 0;
+ j = 0;
+ while (AVAILABLE (haystack, haystack_len, j, needle_len))
+ {
+ const wchar_t *pneedle;
+ const wchar_t *phaystack;
+
+ /* Scan for matches in right half. */
+ i = MAX (suffix, memory);
+ pneedle = &needle[i];
+ phaystack = &haystack[i + j];
+ while (i < needle_len && (CANON_ELEMENT (*pneedle++)
+ == CANON_ELEMENT (*phaystack++)))
+ ++i;
+ if (needle_len <= i)
+ {
+ /* Scan for matches in left half. */
+ i = suffix - 1;
+ pneedle = &needle[i];
+ phaystack = &haystack[i + j];
+ while (memory < i + 1 && (CANON_ELEMENT (*pneedle--)
+ == CANON_ELEMENT (*phaystack--)))
+ --i;
+ if (i + 1 < memory + 1)
+ return (wchar_t *) (haystack + j);
+ /* No match, so remember how many repetitions of period
+ on the right half were scanned. */
+ j += period;
+ memory = needle_len - period;
+ }
+ else
+ {
+ j += i - suffix + 1;
+ memory = 0;
+ }
+ }
+ }
+ else
+ {
+ const wchar_t *phaystack;
+ /* The comparison always starts from needle[suffix], so cache it
+ and use an optimized first-character loop. */
+ wchar_t needle_suffix = CANON_ELEMENT (needle[suffix]);
+
+ /* 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
diff --git a/wcsmbs/wcsstr.c b/wcsmbs/wcsstr.c
index 78f1cc9ce0..7e791a5356 100644
--- a/wcsmbs/wcsstr.c
+++ b/wcsmbs/wcsstr.c
@@ -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
@@ -15,82 +16,41 @@
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"
+
+/* Hash character pairs so a small shift table can be used. All bits of
+ p[0] are included, but not all bits from p[-1]. So if two equal hashes
+ match on p[-1], p[0] matches too. Hash collisions are harmless and result
+ in smaller shifts. */
+#define hash2(p) (((size_t)(p)[0] - ((size_t)(p)[-1] << 3)) % sizeof (shift))
wchar_t *
wcsstr (const wchar_t *haystack, const wchar_t *needle)
{
- wchar_t b, c;
-
- if ((b = *needle) != L'\0')
- {
- haystack--; /* possible ANSI violation */
- do
- if ((c = *++haystack) == L'\0')
- goto ret0;
- while (c != b);
-
- 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;
+ const wchar_t *hs = (const wchar_t *) haystack;
+ const wchar_t *ne = (const wchar_t *) needle;
+
+ /* 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 (ne);
+ size_t hs_len = __wcsnlen (hs, ne_len | 128);
+ if (hs_len < ne_len)
+ return NULL;
+
+ /* Check whether we have a match. This improves performance since we
+ avoid initialization overheads. */
+ if (__wmemcmp (hs, ne, ne_len) == 0)
+ return (wchar_t *) hs;
+
+ return two_way_short_needle (hs, hs_len, ne, ne_len);
}
/* This alias is for backward compatibility with drafts of the ISO C
standard. Unfortunately the Unix(TM) standard requires this name. */
--
2.34.1
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-19 20:45 ` [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865) Adhemerval Zanella
@ 2024-02-20 0:15 ` Noah Goldstein
2024-02-20 11:56 ` Adhemerval Zanella Netto
0 siblings, 1 reply; 10+ messages in thread
From: Noah Goldstein @ 2024-02-20 0:15 UTC (permalink / raw)
To: Adhemerval Zanella; +Cc: libc-alpha
On Mon, Feb 19, 2024 at 8:45 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> 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.
> ---
> wcsmbs/wcs-two-way.h | 312 +++++++++++++++++++++++++++++++++++++++++++
> wcsmbs/wcsstr.c | 104 +++++----------
> 2 files changed, 344 insertions(+), 72 deletions(-)
> create mode 100644 wcsmbs/wcs-two-way.h
>
> diff --git a/wcsmbs/wcs-two-way.h b/wcsmbs/wcs-two-way.h
> new file mode 100644
> index 0000000000..2dcee7fc1a
> --- /dev/null
> +++ b/wcsmbs/wcs-two-way.h
> @@ -0,0 +1,312 @@
> +/* Byte-wise substring search, using the Two-Way algorithm.
> + Copyright (C) 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library 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
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +/* Before including this file, you need to include <string.h> (and
> + <config.h> before that, if not part of libc), and define:
> + AVAILABLE(h, h_l, j, n_l)
> + A macro that returns nonzero if there are
> + at least N_L characters left starting at H[J].
> + H is 'wchar_t *', H_L, J, and N_L are 'size_t';
> + H_L is an lvalue. For NUL-terminated searches,
> + H_L can be modified each iteration to avoid
> + having to compute the end of H up front.
> +
> + For case-insensitivity, you may optionally define:
> + CMP_FUNC(p1, p2, l) A macro that returns 0 iff the first L
> + characters of P1 and P2 are equal.
> + CANON_ELEMENT(c) A macro that canonicalizes an element right after
> + it has been fetched from one of the two strings.
> + The argument is an 'wchar_t'; the result must
> + be an 'wchar_t' as well.
> +*/
> +
> +#include <limits.h>
> +#include <stdint.h>
> +#include <sys/param.h> /* Defines MAX. */
> +
> +/* We use the Two-Way string matching algorithm, which guarantees
> + linear complexity with constant space.
> +
> + See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
> + and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
> +*/
> +
> +#ifndef CANON_ELEMENT
> +# define CANON_ELEMENT(c) c
> +#endif
> +#ifndef CMP_FUNC
> +# define CMP_FUNC __wmemcmp
> +#endif
> +
> +/* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN.
> + Return the index of the first character in the right half, and set
> + *PERIOD to the global period of the right half.
> +
> + The global period of a string is the smallest index (possibly its
> + length) at which all remaining bytes in the string are repetitions
> + of the prefix (the last repetition may be a subset of the prefix).
> +
> + When NEEDLE is factored into two halves, a local period is the
> + length of the smallest word that shares a suffix with the left half
> + and shares a prefix with the right half. All factorizations of a
> + non-empty NEEDLE have a local period of at least 1 and no greater
> + than NEEDLE_LEN.
> +
> + A critical factorization has the property that the local period
> + equals the global period. All strings have at least one critical
> + factorization with the left half smaller than the global period.
> +
> + Given an ordered alphabet, a critical factorization can be computed
> + in linear time, with 2 * NEEDLE_LEN comparisons, by computing the
> + larger of two ordered maximal suffixes. The ordered maximal
> + suffixes are determined by lexicographic comparison of
> + periodicity. */
> +static size_t
> +critical_factorization (const wchar_t *needle, size_t needle_len,
> + size_t *period)
> +{
> + /* Index of last character of left half, or SIZE_MAX. */
> + size_t max_suffix, max_suffix_rev;
> + size_t j; /* Index into NEEDLE for current candidate suffix. */
> + size_t k; /* Offset into current period. */
> + size_t p; /* Intermediate period. */
> + wchar_t a, b; /* Current comparison bytes. */
> +
> + /* Special case NEEDLE_LEN of 1 or 2 (all callers already filtered
> + out 0-length needles. */
> + if (needle_len < 3)
> + {
> + *period = 1;
> + return needle_len - 1;
> + }
> +
> + /* Invariants:
> + 0 <= j < NEEDLE_LEN - 1
> + -1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
> + min(max_suffix, max_suffix_rev) < global period of NEEDLE
> + 1 <= p <= global period of NEEDLE
> + p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j]
> + 1 <= k <= p
> + */
> +
> + /* Perform lexicographic search. */
> + max_suffix = SIZE_MAX;
> + j = 0;
> + k = p = 1;
> + while (j + k < needle_len)
> + {
> + a = CANON_ELEMENT (needle[j + k]);
> + b = CANON_ELEMENT (needle[max_suffix + k]);
> + if (a < b)
> + {
> + /* Suffix is smaller, period is entire prefix so far. */
> + j += k;
> + k = 1;
> + p = j - max_suffix;
> + }
> + else if (a == b)
> + {
> + /* Advance through repetition of the current period. */
> + if (k != p)
> + ++k;
> + else
> + {
> + j += p;
> + k = 1;
> + }
> + }
> + else /* b < a */
> + {
> + /* Suffix is larger, start over from current location. */
> + max_suffix = j++;
> + k = p = 1;
> + }
> + }
> + *period = p;
> +
> + /* Perform reverse lexicographic search. */
> + max_suffix_rev = SIZE_MAX;
> + j = 0;
> + k = p = 1;
> + while (j + k < needle_len)
> + {
> + a = CANON_ELEMENT (needle[j + k]);
> + b = CANON_ELEMENT (needle[max_suffix_rev + k]);
> + if (b < a)
> + {
> + /* Suffix is smaller, period is entire prefix so far. */
> + j += k;
> + k = 1;
> + p = j - max_suffix_rev;
> + }
> + else if (a == b)
> + {
> + /* Advance through repetition of the current period. */
> + if (k != p)
> + ++k;
> + else
> + {
> + j += p;
> + k = 1;
> + }
> + }
> + else /* a < b */
> + {
> + /* Suffix is larger, start over from current location. */
> + max_suffix_rev = j++;
> + k = p = 1;
> + }
> + }
> +
> + /* Choose the shorted suffix. Return the first character of the right
> + half, rather than the last character of the left half. */
> + if (max_suffix_rev + 1 < max_suffix + 1)
> + return max_suffix + 1;
> + *period = p;
> + return max_suffix_rev + 1;
> +}
> +
> +/* Return the first location of non-empty NEEDLE within HAYSTACK, or
> + NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK.
> +
> + If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at
> + most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching.
> + If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 *
> + HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching. */
> +static inline wchar_t *
> +two_way_short_needle (const wchar_t *haystack, size_t haystack_len,
> + const wchar_t *needle, size_t needle_len)
> +{
> + size_t i; /* Index into current character of NEEDLE. */
> + size_t j; /* Index into current window of HAYSTACK. */
> + size_t period; /* The period of the right half of needle. */
> + size_t suffix; /* The index of the right half of needle. */
> +
> + /* Factor the needle into two halves, such that the left half is
> + smaller than the global period, and the right half is
> + periodic (with a period as large as NEEDLE_LEN - suffix). */
> + suffix = critical_factorization (needle, needle_len, &period);
> +
> + /* Perform the search. Each iteration compares the right half
> + first. */
> + if (CMP_FUNC (needle, needle + period, suffix) == 0)
> + {
> + /* Entire needle is periodic; a mismatch can only advance by the
> + period, so use memory to avoid rescanning known occurrences
> + of the period. */
> + size_t memory = 0;
> + j = 0;
> + while (AVAILABLE (haystack, haystack_len, j, needle_len))
> + {
> + const wchar_t *pneedle;
> + const wchar_t *phaystack;
> +
> + /* Scan for matches in right half. */
> + i = MAX (suffix, memory);
> + pneedle = &needle[i];
> + phaystack = &haystack[i + j];
> + while (i < needle_len && (CANON_ELEMENT (*pneedle++)
> + == CANON_ELEMENT (*phaystack++)))
> + ++i;
> + if (needle_len <= i)
> + {
> + /* Scan for matches in left half. */
> + i = suffix - 1;
> + pneedle = &needle[i];
> + phaystack = &haystack[i + j];
> + while (memory < i + 1 && (CANON_ELEMENT (*pneedle--)
> + == CANON_ELEMENT (*phaystack--)))
> + --i;
> + if (i + 1 < memory + 1)
> + return (wchar_t *) (haystack + j);
> + /* No match, so remember how many repetitions of period
> + on the right half were scanned. */
> + j += period;
> + memory = needle_len - period;
> + }
> + else
> + {
> + j += i - suffix + 1;
> + memory = 0;
> + }
> + }
> + }
> + else
> + {
> + const wchar_t *phaystack;
> + /* The comparison always starts from needle[suffix], so cache it
> + and use an optimized first-character loop. */
> + wchar_t needle_suffix = CANON_ELEMENT (needle[suffix]);
> +
> + /* 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
> diff --git a/wcsmbs/wcsstr.c b/wcsmbs/wcsstr.c
> index 78f1cc9ce0..7e791a5356 100644
> --- a/wcsmbs/wcsstr.c
> +++ b/wcsmbs/wcsstr.c
> @@ -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
> @@ -15,82 +16,41 @@
> 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"
> +
> +/* Hash character pairs so a small shift table can be used. All bits of
> + p[0] are included, but not all bits from p[-1]. So if two equal hashes
> + match on p[-1], p[0] matches too. Hash collisions are harmless and result
> + in smaller shifts. */
> +#define hash2(p) (((size_t)(p)[0] - ((size_t)(p)[-1] << 3)) % sizeof (shift))
>
> wchar_t *
> wcsstr (const wchar_t *haystack, const wchar_t *needle)
> {
any issue with just doing?
```
memmem(haystack, sizeof(wchar_t) * wcslen(haystack), needle,
sizeof(wchar_t) * wcslen(needle))
```
> - wchar_t b, c;
> -
> - if ((b = *needle) != L'\0')
> - {
> - haystack--; /* possible ANSI violation */
> - do
> - if ((c = *++haystack) == L'\0')
> - goto ret0;
> - while (c != b);
> -
> - 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;
> + const wchar_t *hs = (const wchar_t *) haystack;
> + const wchar_t *ne = (const wchar_t *) needle;
> +
> + /* 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 (ne);
> + size_t hs_len = __wcsnlen (hs, ne_len | 128);
> + if (hs_len < ne_len)
> + return NULL;
> +
> + /* Check whether we have a match. This improves performance since we
> + avoid initialization overheads. */
> + if (__wmemcmp (hs, ne, ne_len) == 0)
> + return (wchar_t *) hs;
> +
> + return two_way_short_needle (hs, hs_len, ne, ne_len);
> }
> /* This alias is for backward compatibility with drafts of the ISO C
> standard. Unfortunately the Unix(TM) standard requires this name. */
> --
> 2.34.1
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-20 0:15 ` Noah Goldstein
@ 2024-02-20 11:56 ` Adhemerval Zanella Netto
2024-02-20 13:01 ` Alexander Monakov
0 siblings, 1 reply; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2024-02-20 11:56 UTC (permalink / raw)
To: Noah Goldstein; +Cc: libc-alpha
On 19/02/24 21:15, Noah Goldstein wrote:
> On Mon, Feb 19, 2024 at 8:45 PM Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>> +
>> +/* Hash character pairs so a small shift table can be used. All bits of
>> + p[0] are included, but not all bits from p[-1]. So if two equal hashes
>> + match on p[-1], p[0] matches too. Hash collisions are harmless and result
>> + in smaller shifts. */
>> +#define hash2(p) (((size_t)(p)[0] - ((size_t)(p)[-1] << 3)) % sizeof (shift))
>>
>> wchar_t *
>> wcsstr (const wchar_t *haystack, const wchar_t *needle)
>> {
> any issue with just doing?
> ```
> memmem(haystack, sizeof(wchar_t) * wcslen(haystack), needle,
> sizeof(wchar_t) * wcslen(needle))
> ```
None at all, in fact this is a better simplification. I will update the
patch.
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-20 11:56 ` Adhemerval Zanella Netto
@ 2024-02-20 13:01 ` Alexander Monakov
2024-02-20 13:16 ` Adhemerval Zanella Netto
0 siblings, 1 reply; 10+ messages in thread
From: Alexander Monakov @ 2024-02-20 13:01 UTC (permalink / raw)
To: Adhemerval Zanella Netto; +Cc: Noah Goldstein, libc-alpha
On Tue, 20 Feb 2024, Adhemerval Zanella Netto wrote:
> >> wchar_t *
> >> wcsstr (const wchar_t *haystack, const wchar_t *needle)
> >> {
> > any issue with just doing?
> > ```
> > memmem(haystack, sizeof(wchar_t) * wcslen(haystack), needle,
> > sizeof(wchar_t) * wcslen(needle))
> > ```
>
> None at all, in fact this is a better simplification. I will update the
> patch.
What guarantees that memmem is not going to return a pointer
into the middle of a wide char?
(neither does strstr defer to memmem, avoiding strlen(haystack)
when there's an early match)
Alexander
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-20 13:01 ` Alexander Monakov
@ 2024-02-20 13:16 ` Adhemerval Zanella Netto
2024-02-20 16:07 ` Noah Goldstein
0 siblings, 1 reply; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2024-02-20 13:16 UTC (permalink / raw)
To: Alexander Monakov; +Cc: Noah Goldstein, libc-alpha
On 20/02/24 10:01, Alexander Monakov wrote:
>
> On Tue, 20 Feb 2024, Adhemerval Zanella Netto wrote:
>
>>>> wchar_t *
>>>> wcsstr (const wchar_t *haystack, const wchar_t *needle)
>>>> {
>>> any issue with just doing?
>>> ```
>>> memmem(haystack, sizeof(wchar_t) * wcslen(haystack), needle,
>>> sizeof(wchar_t) * wcslen(needle))
>>> ```
>>
>> None at all, in fact this is a better simplification. I will update the
>> patch.
>
> What guarantees that memmem is not going to return a pointer
> into the middle of a wide char?
>
> (neither does strstr defer to memmem, avoiding strlen(haystack)
> when there's an early match)
My understanding is the interface should be composable since memmem
should be agnostic to the input, although it might not have the best
performance (which I really don't care for wcsstr, the idea is just to
remove the quadratic behavior). Do you have an example where it would
fail?
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-20 13:16 ` Adhemerval Zanella Netto
@ 2024-02-20 16:07 ` Noah Goldstein
2024-02-20 16:37 ` Adhemerval Zanella Netto
0 siblings, 1 reply; 10+ messages in thread
From: Noah Goldstein @ 2024-02-20 16:07 UTC (permalink / raw)
To: Adhemerval Zanella Netto; +Cc: Alexander Monakov, libc-alpha
On Tue, Feb 20, 2024 at 1:16 PM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 20/02/24 10:01, Alexander Monakov wrote:
> >
> > On Tue, 20 Feb 2024, Adhemerval Zanella Netto wrote:
> >
> >>>> wchar_t *
> >>>> wcsstr (const wchar_t *haystack, const wchar_t *needle)
> >>>> {
> >>> any issue with just doing?
> >>> ```
> >>> memmem(haystack, sizeof(wchar_t) * wcslen(haystack), needle,
> >>> sizeof(wchar_t) * wcslen(needle))
> >>> ```
> >>
> >> None at all, in fact this is a better simplification. I will update the
> >> patch.
> >
> > What guarantees that memmem is not going to return a pointer
> > into the middle of a wide char?
> >
> > (neither does strstr defer to memmem, avoiding strlen(haystack)
> > when there's an early match)
>
> My understanding is the interface should be composable since memmem
> should be agnostic to the input, although it might not have the best
> performance (which I really don't care for wcsstr, the idea is just to
> remove the quadratic behavior). Do you have an example where it would
> fail?
Think its a valid issue. Something like:
```
hay = {0x4030201, 0x8070605, 0x0};
nee = {0x6050403, 0x0};
```
Would match a midpoint of 2nd char of hay.
Could probably loop through `memem` and if the result is not aligned to
sizeof(wchar_t), continue from the next byte position.
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 3/3] wcsmbs: Ensure wcstr worst-case linear execution time (BZ 23865)
2024-02-20 16:07 ` Noah Goldstein
@ 2024-02-20 16:37 ` Adhemerval Zanella Netto
0 siblings, 0 replies; 10+ messages in thread
From: Adhemerval Zanella Netto @ 2024-02-20 16:37 UTC (permalink / raw)
To: Noah Goldstein; +Cc: Alexander Monakov, libc-alpha
On 20/02/24 13:07, Noah Goldstein wrote:
> On Tue, Feb 20, 2024 at 1:16 PM Adhemerval Zanella Netto
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>>
>> On 20/02/24 10:01, Alexander Monakov wrote:
>>>
>>> On Tue, 20 Feb 2024, Adhemerval Zanella Netto wrote:
>>>
>>>>>> wchar_t *
>>>>>> wcsstr (const wchar_t *haystack, const wchar_t *needle)
>>>>>> {
>>>>> any issue with just doing?
>>>>> ```
>>>>> memmem(haystack, sizeof(wchar_t) * wcslen(haystack), needle,
>>>>> sizeof(wchar_t) * wcslen(needle))
>>>>> ```
>>>>
>>>> None at all, in fact this is a better simplification. I will update the
>>>> patch.
>>>
>>> What guarantees that memmem is not going to return a pointer
>>> into the middle of a wide char?
>>>
>>> (neither does strstr defer to memmem, avoiding strlen(haystack)
>>> when there's an early match)
>>
>> My understanding is the interface should be composable since memmem
>> should be agnostic to the input, although it might not have the best
>> performance (which I really don't care for wcsstr, the idea is just to
>> remove the quadratic behavior). Do you have an example where it would
>> fail?
>
> Think its a valid issue. Something like:
>
> ```
> hay = {0x4030201, 0x8070605, 0x0};
> nee = {0x6050403, 0x0};
> ```
>
> Would match a midpoint of 2nd char of hay.
>
> Could probably loop through `memem` and if the result is not aligned to
> sizeof(wchar_t), continue from the next byte position.
Right, I realized that we are not memmem for the final null wide byes.
I will add such tests and I think it would be better to use the initial
two_way_short_needle strategy that assures it uses wide chars.
^ permalink raw reply [flat|nested] 10+ messages in thread