-/* Copyright (C) 1991,92,93,94,96,97,98,2000,2004,2007,2008 Free Software
+/* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2014 Free Software
Foundation, Inc.
This file is part of the GNU C Library.
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, write to the Free Software Foundation,
- Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+ with this program; if not, see <http://www.gnu.org/licenses/>. */
/* This particular implementation was written by Eric Blake, 2008. */
/* Specification of memmem. */
#include <string.h>
-#include <limits.h>
-#include <stddef.h>
-#include <stdint.h>
-
#ifndef _LIBC
# define __builtin_expect(expr, val) (expr)
#endif
-/* We use the Two-Way string matching algorithm, which guarantees
- linear complexity with constant space. Additionally, for long
- needles, we also use a bad character shift table similar to the
- Boyer-Moore algorithm to achieve sub-linear performance.
-
- See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
- and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
-*/
-
-/* Point at which computing a bad-byte shift table is likely to be
- worthwhile. Small needles should not compute a table, since it
- adds (1 << CHAR_BIT) + NEEDLE_LEN computations of preparation for a
- speedup no greater than a factor of NEEDLE_LEN. The larger the
- needle, the better the potential performance gain. On the other
- hand, on non-POSIX systems with CHAR_BIT larger than eight, the
- memory required for the table is prohibitive. */
-#if CHAR_BIT < 10
-# define LONG_NEEDLE_THRESHOLD 32U
-#else
-# define LONG_NEEDLE_THRESHOLD SIZE_MAX
-#endif
-
-#define MAX(a, b) ((a < b) ? (b) : (a))
-
-/* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN.
- Return the index of the first byte 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 unsigned char *needle, size_t needle_len,
- size_t *period)
-{
- /* Index of last byte 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. */
- unsigned char a, b; /* Current comparison bytes. */
-
- /* 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 = needle[j + k];
- b = 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 = needle[j + k];
- b = 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 longer suffix. Return the first byte of the right
- half, rather than the last byte 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 NEEDLE within HAYSTACK, or NULL. This
- method requires 0 < NEEDLE_LEN <= HAYSTACK_LEN, and is optimized
- for NEEDLE_LEN < LONG_NEEDLE_THRESHOLD. Performance is linear,
- with 2 * NEEDLE_LEN comparisons in preparation, and at most 2 *
- HAYSTACK_LEN - NEEDLE_LEN comparisons in searching. */
-static void *
-two_way_short_needle (const unsigned char *haystack, size_t haystack_len,
- const unsigned char *needle, size_t needle_len)
-{
- size_t i; /* Index into current byte 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 (memcmp (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 (j <= haystack_len - needle_len)
- {
- /* Scan for matches in right half. */
- i = MAX (suffix, memory);
- while (i < needle_len && needle[i] == haystack[i + j])
- ++i;
- if (needle_len <= i)
- {
- /* Scan for matches in left half. */
- i = suffix - 1;
- while (memory < i + 1 && needle[i] == haystack[i + j])
- --i;
- if (i + 1 < memory + 1)
- return (void *) (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
- {
- /* 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 (j <= haystack_len - needle_len)
- {
- /* Scan for matches in right half. */
- i = suffix;
- while (i < needle_len && needle[i] == haystack[i + j])
- ++i;
- if (needle_len <= i)
- {
- /* Scan for matches in left half. */
- i = suffix - 1;
- while (i != SIZE_MAX && needle[i] == haystack[i + j])
- --i;
- if (i == SIZE_MAX)
- return (void *) (haystack + j);
- j += period;
- }
- else
- j += i - suffix + 1;
- }
- }
- return NULL;
-}
-
-/* Return the first location of NEEDLE within HAYSTACK, or NULL. This
- method requires 0 < NEEDLE_LEN <= HAYSTACK_LEN, and is optimized
- for LONG_NEEDLE_THRESHOLD <= NEEDLE_LEN. Performance is linear,
- with 3 * NEEDLE_LEN + (1U << CHAR_BIT) operations in preparation,
- and at most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons in searching.
- The extra initialization cost allows for potential sublinear
- performance O(HAYSTACK_LEN / NEEDLE_LEN). */
-static void *
-two_way_long_needle (const unsigned char *haystack, size_t haystack_len,
- const unsigned char *needle, size_t needle_len)
-{
- size_t i; /* Index into current byte 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. */
- size_t shift_table[1U << CHAR_BIT]; /* See below. */
-
- /* 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);
-
- /* Populate shift_table. For each possible byte value c,
- shift_table[c] is the distance from the last occurrence of c to
- the end of NEEDLE, or NEEDLE_LEN if c is absent from the NEEDLE.
- shift_table[NEEDLE[NEEDLE_LEN - 1]] contains the only 0. */
- for (i = 0; i < 1U << CHAR_BIT; i++)
- shift_table[i] = needle_len;
- for (i = 0; i < needle_len; i++)
- shift_table[needle[i]] = needle_len - i - 1;
-
- /* Perform the search. Each iteration compares the right half
- first. */
- if (memcmp (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 (j <= haystack_len - needle_len)
- {
- /* Check the last byte first; if it does not match, then
- shift to the next possible match location. */
- size_t shift = shift_table[haystack[j + needle_len - 1]];
- if (0 < shift)
- {
- if (memory && shift < period)
- {
- /* Since needle is periodic, but the last period has
- a byte out of place, there can be no match until
- after the mismatch. */
- shift = needle_len - period;
- memory = 0;
- }
- j += shift;
- continue;
- }
- /* Scan for matches in right half. The last byte has
- already been matched, by virtue of the shift table. */
- i = MAX (suffix, memory);
- while (i < needle_len - 1 && needle[i] == haystack[i + j])
- ++i;
- if (needle_len - 1 <= i)
- {
- /* Scan for matches in left half. */
- i = suffix - 1;
- while (memory < i + 1 && needle[i] == haystack[i + j])
- --i;
- if (i + 1 < memory + 1)
- return (void *) (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
- {
- /* 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 (j <= haystack_len - needle_len)
- {
- /* Check the last byte first; if it does not match, then
- shift to the next possible match location. */
- size_t shift = shift_table[haystack[j + needle_len - 1]];
- if (0 < shift)
- {
- j += shift;
- continue;
- }
- /* Scan for matches in right half. The last byte has
- already been matched, by virtue of the shift table. */
- i = suffix;
- while (i < needle_len - 1 && needle[i] == haystack[i + j])
- ++i;
- if (needle_len - 1 <= i)
- {
- /* Scan for matches in left half. */
- i = suffix - 1;
- while (i != SIZE_MAX && needle[i] == haystack[i + j])
- --i;
- if (i == SIZE_MAX)
- return (void *) (haystack + j);
- j += period;
- }
- else
- j += i - suffix + 1;
- }
- }
- return NULL;
-}
+#define RETURN_TYPE void *
+#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
+#include "str-two-way.h"
/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in
HAYSTACK. */
void *
memmem (const void *haystack_start, size_t haystack_len,
- const void *needle_start, size_t needle_len)
+ const void *needle_start, size_t needle_len)
{
/* Abstract memory is considered to be an array of 'unsigned char' values,
not an array of 'char' values. See ISO C 99 section 6.2.6.1. */
{
haystack = memchr (haystack, *needle, haystack_len);
if (!haystack || __builtin_expect (needle_len == 1, 0))
- return (void *) haystack;
+ return (void *) haystack;
haystack_len -= haystack - (const unsigned char *) haystack_start;
if (haystack_len < needle_len)
- return NULL;
+ return NULL;
return two_way_short_needle (haystack, haystack_len, needle, needle_len);
}
else
}
#undef LONG_NEEDLE_THRESHOLD
-#undef MAX
projects / gnulib.git / blobdiff