Imported Upstream version 0.9.6upstream/0.9.6

1 files changed, 153 insertions, 0 deletions

diff --git a/lib/str-kmp.h b/lib/str-kmp.h
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+/* Substring search in a NUL terminated string of UNIT elements,
+   using the Knuth-Morris-Pratt algorithm.
+   Copyright (C) 2005-2015 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2005.
+
+   This program 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, 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 Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program; if not, see <http://www.gnu.org/licenses/>.  */
+
+/* Before including this file, you need to define:
+     UNIT                    The element type of the needle and haystack.
+     CANON_ELEMENT(c)        A macro that canonicalizes an element right after
+                             it has been fetched from needle or haystack.
+                             The argument is of type UNIT; the result must be
+                             of type UNIT as well.  */
+
+/* Knuth-Morris-Pratt algorithm.
+   See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
+   HAYSTACK is the NUL terminated string in which to search for.
+   NEEDLE is the string to search for in HAYSTACK, consisting of NEEDLE_LEN
+   units.
+   Return a boolean indicating success:
+   Return true and set *RESULTP if the search was completed.
+   Return false if it was aborted because not enough memory was available.  */
+static bool
+knuth_morris_pratt (const UNIT *haystack,
+                    const UNIT *needle, size_t needle_len,
+                    const UNIT **resultp)
+{
+  size_t m = needle_len;
+
+  /* Allocate the table.  */
+  size_t *table = (size_t *) nmalloca (m, sizeof (size_t));
+  if (table == NULL)
+    return false;
+  /* Fill the table.
+     For 0 < i < m:
+       0 < table[i] <= i is defined such that
+       forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x],
+       and table[i] is as large as possible with this property.
+     This implies:
+     1) For 0 < i < m:
+          If table[i] < i,
+          needle[table[i]..i-1] = needle[0..i-1-table[i]].
+     2) For 0 < i < m:
+          rhaystack[0..i-1] == needle[0..i-1]
+          and exists h, i <= h < m: rhaystack[h] != needle[h]
+          implies
+          forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1].
+     table[0] remains uninitialized.  */
+  {
+    size_t i, j;
+
+    /* i = 1: Nothing to verify for x = 0.  */
+    table[1] = 1;
+    j = 0;
+
+    for (i = 2; i < m; i++)
+      {
+        /* Here: j = i-1 - table[i-1].
+           The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold
+           for x < table[i-1], by induction.
+           Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1].  */
+        UNIT b = CANON_ELEMENT (needle[i - 1]);
+
+        for (;;)
+          {
+            /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x]
+               is known to hold for x < i-1-j.
+               Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1].  */
+            if (b == CANON_ELEMENT (needle[j]))
+              {
+                /* Set table[i] := i-1-j.  */
+                table[i] = i - ++j;
+                break;
+              }
+            /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
+               for x = i-1-j, because
+                 needle[i-1] != needle[j] = needle[i-1-x].  */
+            if (j == 0)
+              {
+                /* The inequality holds for all possible x.  */
+                table[i] = i;
+                break;
+              }
+            /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
+               for i-1-j < x < i-1-j+table[j], because for these x:
+                 needle[x..i-2]
+                 = needle[x-(i-1-j)..j-1]
+                 != needle[0..j-1-(x-(i-1-j))]  (by definition of table[j])
+                    = needle[0..i-2-x],
+               hence needle[x..i-1] != needle[0..i-1-x].
+               Furthermore
+                 needle[i-1-j+table[j]..i-2]
+                 = needle[table[j]..j-1]
+                 = needle[0..j-1-table[j]]  (by definition of table[j]).  */
+            j = j - table[j];
+          }
+        /* Here: j = i - table[i].  */
+      }
+  }
+
+  /* Search, using the table to accelerate the processing.  */
+  {
+    size_t j;
+    const UNIT *rhaystack;
+    const UNIT *phaystack;
+
+    *resultp = NULL;
+    j = 0;
+    rhaystack = haystack;
+    phaystack = haystack;
+    /* Invariant: phaystack = rhaystack + j.  */
+    while (*phaystack != 0)
+      if (CANON_ELEMENT (needle[j]) == CANON_ELEMENT (*phaystack))
+        {
+          j++;
+          phaystack++;
+          if (j == m)
+            {
+              /* The entire needle has been found.  */
+              *resultp = rhaystack;
+              break;
+            }
+        }
+      else if (j > 0)
+        {
+          /* Found a match of needle[0..j-1], mismatch at needle[j].  */
+          rhaystack += table[j];
+          j -= table[j];
+        }
+      else
+        {
+          /* Found a mismatch at needle[0] already.  */
+          rhaystack++;
+          phaystack++;
+        }
+  }
+
+  freea (table);
+  return true;
+}
+
+#undef CANON_ELEMENT