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>

1 files changed, 3 insertions, 352 deletions

diff --git a/lib/memmem.c b/lib/memmem.c
index 622a034b6d..186d840096 100644
--- 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 @@ memmem (const void *haystack_start, size_t haystack_len,
 }
 
 #undef LONG_NEEDLE_THRESHOLD
-#undef MAX