| /* SPDX-License-Identifier: BSD-3-Clause */ |
| /* |
| * Copyright (c) 1994-2009 Red Hat, Inc. |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are met: |
| * |
| * 1. Redistributions of source code must retain the above copyright notice, |
| * this list of conditions and the following disclaimer. |
| * |
| * 2. Redistributions in binary form must reproduce the above copyright notice, |
| * this list of conditions and the following disclaimer in the documentation |
| * and/or other materials provided with the distribution. |
| * |
| * 3. Neither the name of the copyright holder nor the names of its |
| * contributors may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE |
| * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| /* Byte-wise substring search, using the Two-Way algorithm. |
| * Copyright (C) 2008, 2010 Eric Blake |
| * Permission to use, copy, modify, and distribute this software |
| * is freely granted, provided that this notice is preserved. |
| */ |
| |
| |
| /* Before including this file, you need to include <string.h>, and define: |
| RESULT_TYPE A macro that expands to the return type. |
| AVAILABLE(h, h_l, j, n_l) A macro that returns nonzero if there are |
| at least N_L bytes left starting at |
| H[J]. H is 'unsigned char *', 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 'unsigned char'; the result must |
| be an 'unsigned char' as well. |
| |
| This file undefines the macros documented above, and defines |
| LONG_NEEDLE_THRESHOLD. |
| */ |
| |
| #include <limits.h> |
| #include <stdint.h> |
| |
| /* 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 improved (potentially 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)) |
| |
| #ifndef CANON_ELEMENT |
| # define CANON_ELEMENT(c) c |
| #endif |
| #ifndef CMP_FUNC |
| # define CMP_FUNC memcmp |
| #endif |
| |
| /* 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 = CANON_ELEMENT (needle[j + k]); |
| b = CANON_ELEMENT (needle[(size_t)(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 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 non-empty NEEDLE within HAYSTACK, or |
| NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK. This |
| method is optimized for NEEDLE_LEN < LONG_NEEDLE_THRESHOLD. |
| Performance is guaranteed to be linear, with an initialization cost |
| of 2 * NEEDLE_LEN comparisons. |
| |
| 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 RETURN_TYPE |
| 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 (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)) |
| { |
| /* Scan for matches in right half. */ |
| i = MAX (suffix, memory); |
| while (i < needle_len && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| ++i; |
| if (needle_len <= i) |
| { |
| /* Scan for matches in left half. */ |
| i = suffix - 1; |
| while (memory < i + 1 && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| --i; |
| if (i + 1 < memory + 1) |
| return (RETURN_TYPE) (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 (AVAILABLE (haystack, haystack_len, j, needle_len)) |
| { |
| /* Scan for matches in right half. */ |
| i = suffix; |
| while (i < needle_len && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| ++i; |
| if (needle_len <= i) |
| { |
| /* Scan for matches in left half. */ |
| i = suffix - 1; |
| while (i != SIZE_MAX && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| --i; |
| if (i == SIZE_MAX) |
| return (RETURN_TYPE) (haystack + j); |
| j += period; |
| } |
| else |
| j += i - suffix + 1; |
| } |
| } |
| return NULL; |
| } |
| |
| /* Return the first location of non-empty NEEDLE within HAYSTACK, or |
| NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK. This |
| method is optimized for LONG_NEEDLE_THRESHOLD <= NEEDLE_LEN. |
| Performance is guaranteed to be linear, with an initialization cost |
| of 3 * NEEDLE_LEN + (1 << CHAR_BIT) operations. |
| |
| If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at |
| most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching, |
| and sublinear performance O(HAYSTACK_LEN / NEEDLE_LEN) is possible. |
| If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 * |
| HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching, and |
| sublinear performance is not possible. */ |
| static RETURN_TYPE |
| 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[CANON_ELEMENT (needle[i])] = needle_len - i - 1; |
| |
| /* 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; |
| size_t shift; |
| j = 0; |
| while (AVAILABLE (haystack, haystack_len, j, needle_len)) |
| { |
| /* Check the last byte first; if it does not match, then |
| shift to the next possible match location. */ |
| shift = shift_table[CANON_ELEMENT (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 && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| ++i; |
| if (needle_len - 1 <= i) |
| { |
| /* Scan for matches in left half. */ |
| i = suffix - 1; |
| while (memory < i + 1 && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| --i; |
| if (i + 1 < memory + 1) |
| return (RETURN_TYPE) (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. */ |
| size_t shift; |
| period = MAX (suffix, needle_len - suffix) + 1; |
| j = 0; |
| while (AVAILABLE (haystack, haystack_len, j, needle_len)) |
| { |
| /* Check the last byte first; if it does not match, then |
| shift to the next possible match location. */ |
| shift = shift_table[CANON_ELEMENT (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 && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| ++i; |
| if (needle_len - 1 <= i) |
| { |
| /* Scan for matches in left half. */ |
| i = suffix - 1; |
| while (i != SIZE_MAX && (CANON_ELEMENT (needle[i]) |
| == CANON_ELEMENT (haystack[i + j]))) |
| --i; |
| if (i == SIZE_MAX) |
| return (RETURN_TYPE) (haystack + j); |
| j += period; |
| } |
| else |
| j += i - suffix + 1; |
| } |
| } |
| return NULL; |
| } |
| |
| #undef AVAILABLE |
| #undef CANON_ELEMENT |
| #undef CMP_FUNC |
| #undef MAX |
| #undef RETURN_TYPE |