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changeset 9601:fbf94c8a908a

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Share two-way algorithm. * lib/str-two-way.h: New file, merged from... * lib/memmem.c: ...here... * lib/strstr.c: ...and here. * modules/memmem (Files): Use it. * modules/strstr (Files): Likewise. Signed-off-by: Eric Blake <ebb9@byu.net>
author Eric Blake <ebb9@byu.net>
date Thu, 10 Jan 2008 12:06:35 -0700
parents 99268e709d31
children 7a4db0f92545
files ChangeLog lib/memmem.c lib/str-two-way.h lib/strstr.c modules/memmem-simple modules/strstr
diffstat 6 files changed, 443 insertions(+), 711 deletions(-) [+]
line wrap: on
line diff
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2008-01-10  Eric Blake  <ebb9@byu.net>
 
+	Share two-way algorithm.
+	* lib/str-two-way.h: New file, merged from...
+	* lib/memmem.c: ...here...
+	* lib/strstr.c: ...and here.
+	* modules/memmem (Files): Use it.
+	* modules/strstr (Files): Likewise.
+
 	Avoid quadratic strstr implementations.
 	* lib/strstr.c: New file.
 	* m4/strstr.m4: Likewise.
--- a/lib/memmem.c
+++ b/lib/memmem.c
@@ -25,361 +25,13 @@
 /* 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
@@ -422,4 +74,3 @@
 }
 
 #undef LONG_NEEDLE_THRESHOLD
-#undef MAX
new file mode 100644
--- /dev/null
+++ b/lib/str-two-way.h
@@ -0,0 +1,426 @@
+/* Byte-wise substring search, using the Two-Way algorithm.
+   Copyright (C) 2008 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Written by Eric Blake <ebb9@byu.net>, 2008.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Before including this file, you need to include <config.h> and
+   <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[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 MAX
+#undef RETURN_TYPE
--- a/lib/strstr.c
+++ b/lib/strstr.c
@@ -25,370 +25,17 @@
 /* Specification of strstr.  */
 #include <string.h>
 
-#include <limits.h>
 #include <stdbool.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 better 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 3 *
-   HAYSTACK_LEN - NEEDLE_LEN comparisons in searching.  */
-static char *
-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 (!memchr (&haystack[haystack_len], '\0',
-		      j + needle_len - haystack_len)
-	     && (haystack_len = j + 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 (char *) (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 (!memchr (&haystack[haystack_len], '\0',
-		      j + needle_len - haystack_len)
-	     && (haystack_len = j + 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 (char *) (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 3 * HAYSTACK_LEN - NEEDLE_LEN comparisons in searching.
-   The extra initialization cost allows for as few as HAYSTACK_LEN +
-   HAYSTACK_LEN / NEEDLE_LEN.  */
-static char *
-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 (!memchr (&haystack[haystack_len], '\0',
-		      j + needle_len - haystack_len)
-	     && (haystack_len = j + 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 (char *) (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 (!memchr (&haystack[haystack_len], '\0',
-		      j + needle_len - haystack_len)
-	     && (haystack_len = j + 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 (char *) (haystack + j);
-	      j += period;
-	    }
-	  else
-	    j += i - suffix + 1;
-	}
-    }
-  return NULL;
-}
+#define RETURN_TYPE char *
+#define AVAILABLE(h, h_l, j, n_l)			\
+  (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))	\
+   && ((h_l) = (j) + (n_l)))
+#include "str-two-way.h"
 
 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
    if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
@@ -434,4 +81,3 @@
 }
 
 #undef LONG_NEEDLE_THRESHOLD
-#undef MAX
--- a/modules/memmem-simple
+++ b/modules/memmem-simple
@@ -2,6 +2,7 @@
 memmem() function: locate first substring in a buffer.
 
 Files:
+lib/str-two-way.h
 lib/memmem.c
 m4/memmem.m4
 
--- a/modules/strstr
+++ b/modules/strstr
@@ -2,6 +2,7 @@
 strstr() function: efficiently locate first substring in a buffer.
 
 Files:
+lib/str-two-way.h
 lib/strstr.c
 m4/strstr.m4