Fix performance problem with /k/i and /s/i (Close k-takata/Onigmo#97)

E.g.
For the pattern `/----k/i`, optimization was totally turned off.
Make it possible to use the characters before `k` (i.e. `----`) for
optimization.

k-takata/Onigmo@9c13de8

Author: k-takata

regcomp.c

@@ -4217,7 +4217,7 @@ set_bm_skip(UChar* s, UChar* end, regex_t* reg,
 {
   OnigDistance i, len;
   int clen, flen, n, j, k;
-  UChar *p, buf[ONIGENC_GET_CASE_FOLD_CODES_MAX_NUM][ONIGENC_MBC_CASE_FOLD_MAXLEN];
+  UChar *p, buf[ONIGENC_MBC_CASE_FOLD_MAXLEN];
   OnigCaseFoldCodeItem items[ONIGENC_GET_CASE_FOLD_CODES_MAX_NUM];
   OnigEncoding enc = reg->enc;
 
@@ -4299,14 +4299,42 @@ set_bm_skip(UChar* s, UChar* end, regex_t* reg,
 {
   OnigDistance i, len;
   int clen, flen, n, j, k;
-  UChar *p, buf[ONIGENC_GET_CASE_FOLD_CODES_MAX_NUM][ONIGENC_MBC_CASE_FOLD_MAXLEN];
+  UChar *p, buf[ONIGENC_MBC_CASE_FOLD_MAXLEN];
   OnigCaseFoldCodeItem items[ONIGENC_GET_CASE_FOLD_CODES_MAX_NUM];
   OnigEncoding enc = reg->enc;
 
   len = end - s;
   if (len < ONIG_CHAR_TABLE_SIZE) {
     for (i = 0; i < ONIG_CHAR_TABLE_SIZE; i++) skip[i] = (UChar )(len + 1);
 
+    if (ignore_case) {
+      for (i = 0; i < len; i += clen) {
+        p = s + i;
+        n = ONIGENC_GET_CASE_FOLD_CODES_BY_STR(enc, reg->case_fold_flag,
+            p, end, items);
+        clen = enclen(enc, p, end);
+        if (p + clen > end)
+          clen = (int )(end - p);
+
+        for (j = 0; j < n; j++) {
+          if ((items[j].code_len != 1) || (items[j].byte_len != clen)) {
+            /* Different length isn't supported. Stop optimization at here. */
+            end = p;
+            goto endcheck;
+          }
+          flen = ONIGENC_CODE_TO_MBC(enc, items[j].code[0], buf);
+          if (flen != clen) {
+            /* Different length isn't supported. Stop optimization at here. */
+            end = p;
+            goto endcheck;
+          }
+        }
+      }
+endcheck:
+      ;
+    }
+
+    len = end - s;
     n = 0;
     for (i = 0; i < len; i += clen) {
       p = s + i;
@@ -4317,17 +4345,11 @@ set_bm_skip(UChar* s, UChar* end, regex_t* reg,
       if (p + clen > end)
         clen = (int )(end - p);
 
-      for (j = 0; j < n; j++) {
-        if ((items[j].code_len != 1) || (items[j].byte_len != clen))
-          return 1;  /* different length isn't supported. */
-        flen = ONIGENC_CODE_TO_MBC(enc, items[j].code[0], buf[j]);
-        if (flen != clen)
-          return 1;  /* different length isn't supported. */
-      }
       for (j = 0; j < clen; j++) {
         skip[s[i + j]] = (UChar )(len - i - j);
         for (k = 0; k < n; k++) {
-          skip[buf[k][j]] = (UChar )(len - i - j);
+          ONIGENC_CODE_TO_MBC(enc, items[k].code[0], buf);
+          skip[buf[j]] = (UChar )(len - i - j);
         }
       }
     }
@@ -4369,7 +4391,7 @@ set_bm_skip(UChar* s, UChar* end, regex_t* reg,
     }
 # endif
   }
-  return 0;
+  return (int)len;
 }
 #endif /* USE_SUNDAY_QUICK_SEARCH */
 
@@ -5342,7 +5364,6 @@ optimize_node_left(Node* node, NodeOptInfo* opt, OptEnv* env)
 static int
 set_optimize_exact_info(regex_t* reg, OptExactInfo* e)
 {
-  int r;
   int allow_reverse;
 
   if (e->len == 0) return 0;
@@ -5357,31 +5378,29 @@ set_optimize_exact_info(regex_t* reg, OptExactInfo* e)
 
   if (e->ignore_case > 0) {
     if (e->len >= 3 || (e->len >= 2 && allow_reverse)) {
-      r = set_bm_skip(reg->exact, reg->exact_end, reg,
+      e->len = set_bm_skip(reg->exact, reg->exact_end, reg,
                       reg->map, &(reg->int_map), 1);
-      if (r == 0) {
+      reg->exact_end = reg->exact + e->len;
+      if (e->len >= 3) {
         reg->optimize = (allow_reverse != 0
                          ? ONIG_OPTIMIZE_EXACT_BM_IC : ONIG_OPTIMIZE_EXACT_BM_NOT_REV_IC);
       }
-      else {
+      else if (e->len > 0) {
         reg->optimize = ONIG_OPTIMIZE_EXACT_IC;
       }
+      else
+        return 0;
     }
     else {
       reg->optimize = ONIG_OPTIMIZE_EXACT_IC;
     }
   }
   else {
     if (e->len >= 3 || (e->len >= 2 && allow_reverse)) {
-      r = set_bm_skip(reg->exact, reg->exact_end, reg,
-                      reg->map, &(reg->int_map), 0);
-      if (r == 0) {
-        reg->optimize = (allow_reverse != 0
-                       ? ONIG_OPTIMIZE_EXACT_BM : ONIG_OPTIMIZE_EXACT_BM_NOT_REV);
-      }
-      else {
-        reg->optimize = ONIG_OPTIMIZE_EXACT;
-      }
+      set_bm_skip(reg->exact, reg->exact_end, reg,
+                  reg->map, &(reg->int_map), 0);
+      reg->optimize = (allow_reverse != 0
+                     ? ONIG_OPTIMIZE_EXACT_BM : ONIG_OPTIMIZE_EXACT_BM_NOT_REV);
     }
     else {
       reg->optimize = ONIG_OPTIMIZE_EXACT;