[Feature] Add two way substring search algorithm

diff --git a/src/libutil/str_util.c b/src/libutil/str_util.c
index 513c00d85bd9edc63d7109e70dcf007d80bde90a..384a3ffdb81b092ca0541446c70b8500b178ac16 100644 (file)
--- a/src/libutil/str_util.c
+++ b/src/libutil/str_util.c
@@ -1259,6 +1259,164 @@ rspamd_substring_search_caseless (const gchar *in, gsize inlen,
        return -1;
 }
 
+/* Computing of the maximal suffix for <= */
+static inline gint
+rspamd_two_way_max_suffix (const gchar *x, gint m, gint *p)
+{
+       gint ms, j, k;
+       gchar a, b;
+
+       ms = -1;
+       j = 0;
+       k = *p = 1;
+
+       while (j + k < m) {
+               a = x[j + k];
+               b = x[ms + k];
+
+               if (a < b) {
+                       j += k;
+                       k = 1;
+                       *p = j - ms;
+               }
+               else if (a == b)
+                       if (k != *p)
+                               ++k;
+                       else {
+                               j += *p;
+                               k = 1;
+                       }
+               else { /* a > b */
+                       ms = j;
+                       j = ms + 1;
+                       k = *p = 1;
+               }
+       }
+
+       return (ms);
+}
+
+/* Computing of the maximal suffix for >= */
+static inline gint
+rspamd_two_way_max_suffix_tilde (const gchar *x, gint m, gint *p)
+{
+       gint ms, j, k;
+       gchar a, b;
+
+       ms = -1;
+       j = 0;
+       k = *p = 1;
+
+       while (j + k < m) {
+               a = x[j + k];
+               b = x[ms + k];
+
+               if (a > b) {
+                       j += k;
+                       k = 1;
+                       *p = j - ms;
+               }
+               else if (a == b)
+                       if (k != *p)
+                               ++k;
+                       else {
+                               j += *p;
+                               k = 1;
+                       }
+               else { /* a < b */
+                       ms = j;
+                       j = ms + 1;
+                       k = *p = 1;
+               }
+       }
+       return (ms);
+}
+
+/* Two Way string matching algorithm. */
+goffset
+rspamd_substring_search_twoway (const gchar *in, gint inlen,
+               const gchar *srch, gint srchlen)
+{
+       int i, j, ell, memory, p, per, q;
+
+       /* Preprocessing */
+       i = rspamd_two_way_max_suffix (in, inlen, &p);
+       j = rspamd_two_way_max_suffix_tilde (in, inlen, &q);
+
+       if (i > j) {
+               ell = i;
+               per = p;
+       }
+       else {
+               ell = j;
+               per = q;
+       }
+
+       /* Searching */
+       if (memcmp (in, in + per, ell + 1) == 0) {
+               j = 0;
+               memory = -1;
+
+               while (j <= srchlen - inlen) {
+                       i = MAX (ell, memory) + 1;
+
+                       while (i < inlen && in[i] == srch[i + j]) {
+                               i ++;
+                       }
+
+                       if (i >= inlen) {
+                               i = ell;
+
+                               while (i > memory && in[i] == srch[i + j]) {
+                                       i --;
+                               }
+
+                               if (i <= memory) {
+                                       return j;
+                               }
+
+                               j += per;
+                               memory = inlen - per - 1;
+                       }
+                       else {
+                               j += (i - ell);
+                               memory = -1;
+                       }
+               }
+       }
+       else {
+               per = MAX (ell + 1, inlen - ell - 1) + 1;
+               j = 0;
+
+               while (j <= srchlen - inlen) {
+                       i = ell + 1;
+
+                       while (i < inlen && in[i] == srch[i + j]) {
+                               i ++;
+                       }
+
+                       if (i >= inlen) {
+                               i = ell;
+
+                               while (i >= 0 && in[i] == srch[i + j]) {
+                                       i --;
+                               }
+
+                               if (i < 0) {
+                                       return j;
+                               }
+
+                               j += per;
+                       }
+                       else
+                               j += (i - ell);
+               }
+       }
+
+       return -1;
+}
+
+
 goffset
 rspamd_string_find_eoh (GString *input)
 {

diff --git a/src/libutil/str_util.h b/src/libutil/str_util.h
index 04132a4d373e96f0bf65f80623fe1ff89d723d48..68f84f7bc6afcea7a1869a7ae7af4998008f02a0 100644 (file)
--- a/src/libutil/str_util.h
+++ b/src/libutil/str_util.h
@@ -251,6 +251,17 @@ goffset rspamd_substring_search (const gchar *in, gsize inlen,
 goffset rspamd_substring_search_caseless (const gchar *in, gsize inlen,
                const gchar *srch, gsize srchlen);
 
+/**
+ * Search for a substring `srch` in the text `in` using 2-way algorithm:
+ * http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
+ * @param in input
+ * @param inlen input len
+ * @param srch search string
+ * @param srchlen length of the search string
+ * @return position of the first substring match or (-1) if not found
+ */
+goffset rspamd_substring_search_twoway (const gchar *in, gint inlen,
+               const gchar *srch, gint srchlen);
 
 /**
  * Search for end-of-headers mark in the input string. Returns position just after