diff --git a/enc/unicode.c b/enc/unicode.c
index cbfc6cdf589681..07497cdbe46731 100644
--- a/enc/unicode.c
+++ b/enc/unicode.c
@@ -682,15 +682,13 @@ onigenc_unicode_case_map(OnigCaseFoldType* flagP,
     *pp += codepoint_length;
 
     if (code <= 'z') { /* ASCII comes first */
-      if (code >= 'a' && code <= 'z') {
+      if (code >= 'a' /*&& code <= 'z'*/) {
 	if (flags & ONIGENC_CASE_UPCASE) {
 	  MODIFIED;
 	  if (flags & ONIGENC_CASE_FOLD_TURKISH_AZERI && code == 'i')
 	    code = I_WITH_DOT_ABOVE;
-          else {
-            code -= 'a';
-            code += 'A';
-          }
+          else
+            code -= 'a' - 'A';
 	}
       }
       else if (code >= 'A' && code <= 'Z') {
diff --git a/regcomp.c b/regcomp.c
index e389e6f1209af5..0ecf162556b777 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -2803,14 +2803,11 @@ get_head_value_node(Node* node, int exact, regex_t* reg)
   case NT_STR:
     {
       StrNode* sn = NSTR(node);
-
       if (sn->end <= sn->s)
         break;
 
-      if (exact != 0 &&
-          !NSTRING_IS_RAW(node) && IS_IGNORECASE(reg->options)) {
-      }
-      else {
+      if (exact == 0 ||
+          NSTRING_IS_RAW(node) || !IS_IGNORECASE(reg->options)) {
         n = node;
       }
     }
@@ -3301,6 +3298,14 @@ setup_subexp_call(Node* node, ScanEnv* env)
 }
 #endif
 
+#define IN_ALT          (1<<0)
+#define IN_NOT          (1<<1)
+#define IN_REPEAT       (1<<2)
+#define IN_VAR_REPEAT   (1<<3)
+#define IN_CALL         (1<<4)
+#define IN_RECCALL      (1<<5)
+#define IN_LOOK_BEHIND  (1<<6)
+
 /* divide different length alternatives in look-behind.
   (?<=A|B) ==> (?<=A)|(?<=B)
   (?<!A|B) ==> (?<!A)(?<!B)
@@ -3597,24 +3602,29 @@ expand_case_fold_string_alt(int item_num, OnigCaseFoldCodeItem items[],
   return ONIGERR_MEMORY;
 }
 
-static int
-expand_case_fold_string(Node* node, regex_t* reg)
-{
 #define THRESHOLD_CASE_FOLD_ALT_FOR_EXPANSION  8
 
+static int
+expand_case_fold_string(Node* node, regex_t* reg, int state)
+{
   int r, n, len, alt_num;
   int varlen = 0;
+  int is_in_look_behind;
   UChar *start, *end, *p;
   Node *top_root, *root, *snode, *prev_node;
   OnigCaseFoldCodeItem items[ONIGENC_GET_CASE_FOLD_CODES_MAX_NUM];
-  StrNode* sn = NSTR(node);
+  StrNode* sn;
 
   if (NSTRING_IS_AMBIG(node)) return 0;
 
+  sn = NSTR(node);
+
   start = sn->s;
   end   = sn->end;
   if (start >= end) return 0;
 
+  is_in_look_behind = (state & IN_LOOK_BEHIND) != 0;
+
   r = 0;
   top_root = root = prev_node = snode = NULL_NODE;
   alt_num = 1;
@@ -3630,7 +3640,7 @@ expand_case_fold_string(Node* node, regex_t* reg)
     len = enclen(reg->enc, p, end);
 
     varlen = is_case_fold_variable_len(n, items, len);
-    if (n == 0 || varlen == 0) {
+    if (n == 0 || varlen == 0 || is_in_look_behind) {
       if (IS_NULL(snode)) {
         if (IS_NULL(root) && IS_NOT_NULL(prev_node)) {
           onig_node_free(top_root);
@@ -3889,13 +3899,6 @@ setup_comb_exp_check(Node* node, int state, ScanEnv* env)
 }
 #endif
 
-#define IN_ALT        (1<<0)
-#define IN_NOT        (1<<1)
-#define IN_REPEAT     (1<<2)
-#define IN_VAR_REPEAT (1<<3)
-#define IN_CALL       (1<<4)
-#define IN_RECCALL    (1<<5)
-
 /* setup_tree does the following work.
  1. check empty loop. (set qn->target_empty_info)
  2. expand ignore-case in char class.
@@ -3937,7 +3940,7 @@ setup_tree(Node* node, regex_t* reg, int state, ScanEnv* env)
 
   case NT_STR:
     if (IS_IGNORECASE(reg->options) && !NSTRING_IS_RAW(node)) {
-      r = expand_case_fold_string(node, reg);
+      r = expand_case_fold_string(node, reg, state);
     }
     break;
 
@@ -4180,7 +4183,7 @@ setup_tree(Node* node, regex_t* reg, int state, ScanEnv* env)
           if (r < 0) return r;
           if (r > 0) return ONIGERR_INVALID_LOOK_BEHIND_PATTERN;
           if (NTYPE(node) != NT_ANCHOR) goto restart;
-          r = setup_tree(an->target, reg, state, env);
+          r = setup_tree(an->target, reg, (state | IN_LOOK_BEHIND), env);
           if (r != 0) return r;
           r = setup_look_behind(node, reg, env);
         }
@@ -4193,7 +4196,8 @@ setup_tree(Node* node, regex_t* reg, int state, ScanEnv* env)
           if (r < 0) return r;
           if (r > 0) return ONIGERR_INVALID_LOOK_BEHIND_PATTERN;
           if (NTYPE(node) != NT_ANCHOR) goto restart;
-          r = setup_tree(an->target, reg, (state | IN_NOT), env);
+          r = setup_tree(an->target, reg, (state | IN_NOT | IN_LOOK_BEHIND),
+                         env);
           if (r != 0) return r;
           r = setup_look_behind(node, reg, env);
         }
@@ -4209,104 +4213,49 @@ setup_tree(Node* node, regex_t* reg, int state, ScanEnv* env)
   return r;
 }
 
-#ifndef USE_SUNDAY_QUICK_SEARCH
-/* set skip map for Boyer-Moore search */
+/* set skip map for Sunday's quick search */
 static int
 set_bm_skip(UChar* s, UChar* end, regex_t* reg,
             UChar skip[], int** int_skip, int ignore_case)
 {
   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;
-
-    n = 0;
-    for (i = 0; i < len - 1; i += clen) {
-      p = s + i;
-      if (ignore_case)
-        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))
-          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 - 1 - i - j);
-        for (k = 0; k < n; k++) {
-          skip[buf[k][j]] = (UChar )(len - 1 - i - j);
-        }
-      }
-    }
-  }
-  else {
-# if OPT_EXACT_MAXLEN < ONIG_CHAR_TABLE_SIZE
-    /* This should not happen. */
-    return ONIGERR_TYPE_BUG;
-# else
-    if (IS_NULL(*int_skip)) {
-      *int_skip = (int* )xmalloc(sizeof(int) * ONIG_CHAR_TABLE_SIZE);
-      if (IS_NULL(*int_skip)) return ONIGERR_MEMORY;
-    }
-    for (i = 0; i < ONIG_CHAR_TABLE_SIZE; i++) (*int_skip)[i] = (int )len;
-
-    n = 0;
-    for (i = 0; i < len - 1; i += clen) {
-      p = s + i;
-      if (ignore_case)
+    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))
-          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++) {
-        (*int_skip)[s[i + j]] = (int )(len - 1 - i - j);
-        for (k = 0; k < n; k++) {
-          (*int_skip)[buf[k][j]] = (int )(len - 1 - i - j);
+            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:
+      ;
     }
-# endif
-  }
-  return 0;
-}
-
-#else /* USE_SUNDAY_QUICK_SEARCH */
-
-/* set skip map for Sunday's quick search */
-static int
-set_bm_skip(UChar* s, UChar* end, regex_t* reg,
-            UChar skip[], int** int_skip, int ignore_case)
-{
-  OnigDistance i, len;
-  int clen, flen, n, j, k;
-  UChar *p, buf[ONIGENC_GET_CASE_FOLD_CODES_MAX_NUM][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);
 
+    len = end - s;
+    for (i = 0; i < ONIG_CHAR_TABLE_SIZE; i++)
+      skip[i] = (UChar )(len + 1);
     n = 0;
     for (i = 0; i < len; i += clen) {
       p = s + i;
@@ -4317,17 +4266,11 @@ 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);
         }
       }
     }
@@ -4369,9 +4312,8 @@ set_bm_skip(UChar* s, UChar* end, regex_t* reg,
     }
 # endif
   }
-  return 0;
+  return (int)len;
 }
-#endif /* USE_SUNDAY_QUICK_SEARCH */
 
 typedef struct {
   OnigDistance min;  /* min byte length */
@@ -5049,7 +4991,7 @@ optimize_node_left(Node* node, NodeOptInfo* opt, OptEnv* env)
 
         if (NSTRING_IS_DONT_GET_OPT_INFO(node)) {
           int n = onigenc_strlen(env->enc, sn->s, sn->end);
-          max = ONIGENC_MBC_MAXLEN_DIST(env->enc) * (OnigDistance)n;
+          max = (OnigDistance )ONIGENC_MBC_MAXLEN_DIST(env->enc) * (OnigDistance)n;
         }
         else {
           concat_opt_exact_info_str(&opt->exb, sn->s, sn->end,
@@ -5232,7 +5174,7 @@ optimize_node_left(Node* node, NodeOptInfo* opt, OptEnv* env)
       r = optimize_node_left(qn->target, &nopt, env);
       if (r) break;
 
-      if (/*qn->lower == 0 &&*/ IS_REPEAT_INFINITE(qn->upper)) {
+      if (qn->lower == 0 && IS_REPEAT_INFINITE(qn->upper)) {
         if (env->mmd.max == 0 &&
             NTYPE(qn->target) == NT_CANY && qn->greedy) {
           if (IS_MULTILINE(env->options))
@@ -5342,7 +5284,6 @@ 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;
@@ -5357,15 +5298,18 @@ 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;
@@ -5373,15 +5317,10 @@ set_optimize_exact_info(regex_t* reg, OptExactInfo* e)
   }
   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;
diff --git a/regenc.c b/regenc.c
index 0afdf22cb7bdc1..823aacc28e615b 100644
--- a/regenc.c
+++ b/regenc.c
@@ -984,7 +984,7 @@ onigenc_ascii_only_case_map(OnigCaseFoldType* flagP, const OnigUChar** pp, const
 
     if (code >= 'a' && code <= 'z' && (flags & ONIGENC_CASE_UPCASE)) {
       flags |= ONIGENC_CASE_MODIFIED;
-      code += 'A' - 'a';
+      code -= 'a' - 'A';
     }
     else if (code >= 'A' && code <= 'Z' &&
         (flags & (ONIGENC_CASE_DOWNCASE | ONIGENC_CASE_FOLD))) {
@@ -1013,7 +1013,7 @@ onigenc_single_byte_ascii_only_case_map(OnigCaseFoldType* flagP, const OnigUChar
 
     if (code >= 'a' && code <= 'z' && (flags & ONIGENC_CASE_UPCASE)) {
       flags |= ONIGENC_CASE_MODIFIED;
-      code += 'A' - 'a';
+      code -= 'a' - 'A';
     }
     else if (code >= 'A' && code <= 'Z' &&
         (flags & (ONIGENC_CASE_DOWNCASE | ONIGENC_CASE_FOLD))) {
diff --git a/regexec.c b/regexec.c
index b8d174ec8ed472..eec3e236631805 100644
--- a/regexec.c
+++ b/regexec.c
@@ -2742,7 +2742,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 
       /* default behavior: return first-matching result. */
       goto finish;
-      NEXT;
 
     CASE(OP_EXACT1)  MOP_IN(OP_EXACT1);
       DATA_ENSURE(1);
@@ -3316,40 +3315,36 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
         if (ON_STR_BEGIN(s) || !ONIGENC_IS_MBC_WORD(encode, sprev, end)) {
           MOP_OUT;
           JUMP;
-        }
+	}
       }
       goto fail;
-      NEXT;
 
     CASE(OP_ASCII_WORD_BEGIN)  MOP_IN(OP_ASCII_WORD_BEGIN);
       if (DATA_ENSURE_CHECK1 && ONIGENC_IS_MBC_ASCII_WORD(encode, s, end)) {
         if (ON_STR_BEGIN(s) || !ONIGENC_IS_MBC_ASCII_WORD(encode, sprev, end)) {
           MOP_OUT;
           JUMP;
-        }
+	}
       }
       goto fail;
-      NEXT;
 
     CASE(OP_WORD_END)  MOP_IN(OP_WORD_END);
       if (!ON_STR_BEGIN(s) && ONIGENC_IS_MBC_WORD(encode, sprev, end)) {
         if (ON_STR_END(s) || !ONIGENC_IS_MBC_WORD(encode, s, end)) {
           MOP_OUT;
           JUMP;
-        }
+	}
       }
       goto fail;
-      NEXT;
 
     CASE(OP_ASCII_WORD_END)  MOP_IN(OP_ASCII_WORD_END);
       if (!ON_STR_BEGIN(s) && ONIGENC_IS_MBC_ASCII_WORD(encode, sprev, end)) {
         if (ON_STR_END(s) || !ONIGENC_IS_MBC_ASCII_WORD(encode, s, end)) {
           MOP_OUT;
           JUMP;
-        }
+	}
       }
       goto fail;
-      NEXT;
 #endif
 
     CASE(OP_BEGIN_BUF)  MOP_IN(OP_BEGIN_BUF);
@@ -3379,10 +3374,9 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 #endif
                 && !ON_STR_END(s)) {
         MOP_OUT;
-        JUMP;
+	JUMP;
       }
       goto fail;
-      NEXT;
 
     CASE(OP_END_LINE)  MOP_IN(OP_END_LINE);
       if (ON_STR_END(s)) {
@@ -3398,10 +3392,9 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
       }
       else if (ONIGENC_IS_MBC_NEWLINE_EX(encode, s, str, end, option, 1)) {
         MOP_OUT;
-        JUMP;
+	JUMP;
       }
       goto fail;
-      NEXT;
 
     CASE(OP_SEMI_END_BUF)  MOP_IN(OP_SEMI_END_BUF);
       if (ON_STR_END(s)) {
@@ -3433,7 +3426,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 #endif
       }
       goto fail;
-      NEXT;
 
     CASE(OP_BEGIN_POSITION)  MOP_IN(OP_BEGIN_POSITION);
       if (s != msa->gpos)
@@ -3499,12 +3491,10 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
     CASE(OP_BACKREF1)  MOP_IN(OP_BACKREF1);
       mem = 1;
       goto backref;
-      NEXT;
 
     CASE(OP_BACKREF2)  MOP_IN(OP_BACKREF2);
       mem = 2;
       goto backref;
-      NEXT;
 
     CASE(OP_BACKREFN)  MOP_IN(OP_BACKREFN);
       GET_MEMNUM_INC(mem, p);
@@ -3934,7 +3924,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
       STACK_GET_REPEAT(mem, stkp);
       si = GET_STACK_INDEX(stkp);
       goto repeat_inc;
-      NEXT;
 
     CASE(OP_REPEAT_INC_NG)  MOP_IN(OP_REPEAT_INC_NG);
       GET_MEMNUM_INC(mem, p); /* mem: OP_REPEAT ID */
@@ -3970,7 +3959,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
       STACK_GET_REPEAT(mem, stkp);
       si = GET_STACK_INDEX(stkp);
       goto repeat_inc_ng;
-      NEXT;
 
     CASE(OP_PUSH_POS)  MOP_IN(OP_PUSH_POS);
       STACK_PUSH_POS(s, sprev, pkeep);
@@ -3995,7 +3983,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
     CASE(OP_FAIL_POS)  MOP_IN(OP_FAIL_POS);
       STACK_POP_TIL_POS_NOT;
       goto fail;
-      NEXT;
 
     CASE(OP_PUSH_STOP_BT)  MOP_IN(OP_PUSH_STOP_BT);
       STACK_PUSH_STOP_BT;
@@ -4036,7 +4023,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
     CASE(OP_FAIL_LOOK_BEHIND_NOT)  MOP_IN(OP_FAIL_LOOK_BEHIND_NOT);
       STACK_POP_TIL_LOOK_BEHIND_NOT;
       goto fail;
-      NEXT;
 
     CASE(OP_PUSH_ABSENT_POS)  MOP_IN(OP_PUSH_ABSENT_POS);
       /* Save the absent-start-pos and the original end-pos. */
@@ -4098,7 +4084,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 #endif
       STACK_POP_TIL_ABSENT;
       goto fail;
-      NEXT;
 
 #ifdef USE_SUBEXP_CALL
     CASE(OP_CALL)  MOP_IN(OP_CALL);
@@ -4128,7 +4113,6 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 
     CASE(OP_FINISH)
       goto finish;
-      NEXT;
 
     CASE(OP_FAIL)
       if (0) {
@@ -4393,219 +4377,6 @@ slow_search_backward_ic(OnigEncoding enc, int case_fold_flag,
   return (UChar* )NULL;
 }
 
-#ifndef USE_SUNDAY_QUICK_SEARCH
-/* Boyer-Moore-Horspool search applied to a multibyte string */
-static UChar*
-bm_search_notrev(regex_t* reg, const UChar* target, const UChar* target_end,
-                 const UChar* text, const UChar* text_end,
-                 const UChar* text_range)
-{
-  const UChar *s, *se, *t, *p, *end;
-  const UChar *tail;
-  ptrdiff_t skip, tlen1;
-
-# ifdef ONIG_DEBUG_SEARCH
-  fprintf(stderr, "bm_search_notrev: text: %"PRIuPTR" (%p), text_end: %"PRIuPTR" (%p), text_range: %"PRIuPTR" (%p)\n",
-          (uintptr_t )text, text, (uintptr_t )text_end, text_end, (uintptr_t )text_range, text_range);
-# endif
-
-  tail = target_end - 1;
-  tlen1 = tail - target;
-  end = text_range;
-  if (end + tlen1 > text_end)
-    end = text_end - tlen1;
-
-  s = text;
-
-  if (IS_NULL(reg->int_map)) {
-    while (s < end) {
-      p = se = s + tlen1;
-      t = tail;
-      while (*p == *t) {
-        if (t == target) return (UChar* )s;
-        p--; t--;
-      }
-      skip = reg->map[*se];
-      t = s;
-      do {
-        s += enclen(reg->enc, s, end);
-      } while ((s - t) < skip && s < end);
-    }
-  }
-  else {
-# if OPT_EXACT_MAXLEN >= ONIG_CHAR_TABLE_SIZE
-    while (s < end) {
-      p = se = s + tlen1;
-      t = tail;
-      while (*p == *t) {
-        if (t == target) return (UChar* )s;
-        p--; t--;
-      }
-      skip = reg->int_map[*se];
-      t = s;
-      do {
-        s += enclen(reg->enc, s, end);
-      } while ((s - t) < skip && s < end);
-    }
-# endif
-  }
-
-  return (UChar* )NULL;
-}
-
-/* Boyer-Moore-Horspool search */
-static UChar*
-bm_search(regex_t* reg, const UChar* target, const UChar* target_end,
-          const UChar* text, const UChar* text_end, const UChar* text_range)
-{
-  const UChar *s, *t, *p, *end;
-  const UChar *tail;
-
-# ifdef ONIG_DEBUG_SEARCH
-  fprintf(stderr, "bm_search: text: %"PRIuPTR" (%p), text_end: %"PRIuPTR" (%p), text_range: %"PRIuPTR" (%p)\n",
-          (uintptr_t )text, text, (uintptr_t )text_end, text_end, (uintptr_t )text_range, text_range);
-# endif
-
-  end = text_range + (target_end - target) - 1;
-  if (end > text_end)
-    end = text_end;
-
-  tail = target_end - 1;
-  s = text + (target_end - target) - 1;
-  if (IS_NULL(reg->int_map)) {
-    while (s < end) {
-      p = s;
-      t = tail;
-# ifdef ONIG_DEBUG_SEARCH
-      fprintf(stderr, "bm_search_loop: pos: %"PRIdPTR" %s\n",
-          (intptr_t )(s - text), s);
-# endif
-      while (*p == *t) {
-        if (t == target) return (UChar* )p;
-        p--; t--;
-      }
-      s += reg->map[*s];
-    }
-  }
-  else { /* see int_map[] */
-# if OPT_EXACT_MAXLEN >= ONIG_CHAR_TABLE_SIZE
-    while (s < end) {
-      p = s;
-      t = tail;
-      while (*p == *t) {
-        if (t == target) return (UChar* )p;
-        p--; t--;
-      }
-      s += reg->int_map[*s];
-    }
-# endif
-  }
-  return (UChar* )NULL;
-}
-
-/* Boyer-Moore-Horspool search applied to a multibyte string (ignore case) */
-static UChar*
-bm_search_notrev_ic(regex_t* reg, const UChar* target, const UChar* target_end,
-                    const UChar* text, const UChar* text_end,
-                    const UChar* text_range)
-{
-  const UChar *s, *se, *t, *end;
-  const UChar *tail;
-  ptrdiff_t skip, tlen1;
-  OnigEncoding enc = reg->enc;
-  int case_fold_flag = reg->case_fold_flag;
-
-# ifdef ONIG_DEBUG_SEARCH
-  fprintf(stderr, "bm_search_notrev_ic: text: %d (%p), text_end: %d (%p), text_range: %d (%p)\n",
-          (int )text, text, (int )text_end, text_end, (int )text_range, text_range);
-# endif
-
-  tail = target_end - 1;
-  tlen1 = tail - target;
-  end = text_range;
-  if (end + tlen1 > text_end)
-    end = text_end - tlen1;
-
-  s = text;
-
-  if (IS_NULL(reg->int_map)) {
-    while (s < end) {
-      se = s + tlen1;
-      if (str_lower_case_match(enc, case_fold_flag, target, target_end,
-                               s, se + 1))
-        return (UChar* )s;
-      skip = reg->map[*se];
-      t = s;
-      do {
-        s += enclen(reg->enc, s, end);
-      } while ((s - t) < skip && s < end);
-    }
-  }
-  else {
-# if OPT_EXACT_MAXLEN >= ONIG_CHAR_TABLE_SIZE
-    while (s < end) {
-      se = s + tlen1;
-      if (str_lower_case_match(enc, case_fold_flag, target, target_end,
-                               s, se + 1))
-        return (UChar* )s;
-      skip = reg->int_map[*se];
-      t = s;
-      do {
-        s += enclen(reg->enc, s, end);
-      } while ((s - t) < skip && s < end);
-    }
-# endif
-  }
-
-  return (UChar* )NULL;
-}
-
-/* Boyer-Moore-Horspool search (ignore case) */
-static UChar*
-bm_search_ic(regex_t* reg, const UChar* target, const UChar* target_end,
-             const UChar* text, const UChar* text_end, const UChar* text_range)
-{
-  const UChar *s, *p, *end;
-  const UChar *tail;
-  OnigEncoding enc = reg->enc;
-  int case_fold_flag = reg->case_fold_flag;
-
-# ifdef ONIG_DEBUG_SEARCH
-  fprintf(stderr, "bm_search_ic: text: %d (%p), text_end: %d (%p), text_range: %d (%p)\n",
-          (int )text, text, (int )text_end, text_end, (int )text_range, text_range);
-# endif
-
-  end = text_range + (target_end - target) - 1;
-  if (end > text_end)
-    end = text_end;
-
-  tail = target_end - 1;
-  s = text + (target_end - target) - 1;
-  if (IS_NULL(reg->int_map)) {
-    while (s < end) {
-      p = s - (target_end - target) + 1;
-      if (str_lower_case_match(enc, case_fold_flag, target, target_end,
-                               p, s + 1))
-        return (UChar* )p;
-      s += reg->map[*s];
-    }
-  }
-  else { /* see int_map[] */
-# if OPT_EXACT_MAXLEN >= ONIG_CHAR_TABLE_SIZE
-    while (s < end) {
-      p = s - (target_end - target) + 1;
-      if (str_lower_case_match(enc, case_fold_flag, target, target_end,
-                               p, s + 1))
-        return (UChar* )p;
-      s += reg->int_map[*s];
-    }
-# endif
-  }
-  return (UChar* )NULL;
-}
-
-#else /* USE_SUNDAY_QUICK_SEARCH */
-
 /* Sunday's quick search applied to a multibyte string */
 static UChar*
 bm_search_notrev(regex_t* reg, const UChar* target, const UChar* target_end,
@@ -4824,7 +4595,6 @@ bm_search_ic(regex_t* reg, const UChar* target, const UChar* target_end,
   }
   return (UChar* )NULL;
 }
-#endif /* USE_SUNDAY_QUICK_SEARCH */
 
 #ifdef USE_INT_MAP_BACKWARD
 static int
diff --git a/regint.h b/regint.h
index 75abfba235790c..9924e5f62ab5f3 100644
--- a/regint.h
+++ b/regint.h
@@ -86,7 +86,6 @@
 /* #define USE_OP_PUSH_OR_JUMP_EXACT */
 #define USE_QTFR_PEEK_NEXT
 #define USE_ST_LIBRARY
-#define USE_SUNDAY_QUICK_SEARCH
 
 #define INIT_MATCH_STACK_SIZE                     160
 #define DEFAULT_MATCH_STACK_LIMIT_SIZE              0 /* unlimited */
diff --git a/spec/ruby/language/regexp_spec.rb b/spec/ruby/language/regexp_spec.rb
index 0cd9584549b801..dbf341b19ea526 100644
--- a/spec/ruby/language/regexp_spec.rb
+++ b/spec/ruby/language/regexp_spec.rb
@@ -112,7 +112,7 @@
     /foo.(?<=\d)/.match("fooA foo1").to_a.should == ["foo1"]
   end
 
-  ruby_bug "#13671", ""..."3.6" do # https://bugs.ruby-lang.org/issues/13671
+  ruby_bug "#13671", ""..."3.5" do # https://bugs.ruby-lang.org/issues/13671
     it "handles a lookbehind with ss characters" do
       r =  Regexp.new("(?<!dss)", Regexp::IGNORECASE)
       r.should =~ "✨"
diff --git a/test/ruby/test_regexp.rb b/test/ruby/test_regexp.rb
index 9f1e03e6499782..2d7a67dd549c61 100644
--- a/test/ruby/test_regexp.rb
+++ b/test/ruby/test_regexp.rb
@@ -1743,6 +1743,33 @@ def test_conditional_expression
     assert_raise(RegexpError, bug12418){ Regexp.new('(0?0|(?(5)||)|(?(5)||))?') }
   end
 
+  def test_quick_search
+    assert_match_at('(?i) *TOOKY', 'Mozilla/5.0 (Linux; Android 4.0.3; TOOKY', [[34, 40]])   # Issue #120
+  end
+
+  def test_ss_in_look_behind
+    assert_match_at("(?i:ss)", "ss", [[0, 2]])
+    assert_match_at("(?i:ss)", "Ss", [[0, 2]])
+    assert_match_at("(?i:ss)", "SS", [[0, 2]])
+    assert_match_at("(?i:ss)", "\u017fS", [[0, 2]])  # LATIN SMALL LETTER LONG S
+    assert_match_at("(?i:ss)", "s\u017f", [[0, 2]])
+    assert_match_at("(?i:ss)", "\u00df", [[0, 1]])   # LATIN SMALL LETTER SHARP S
+    assert_match_at("(?i:ss)", "\u1e9e", [[0, 1]])   # LATIN CAPITAL LETTER SHARP S
+    assert_match_at("(?i:xssy)", "xssy", [[0, 4]])
+    assert_match_at("(?i:xssy)", "xSsy", [[0, 4]])
+    assert_match_at("(?i:xssy)", "xSSy", [[0, 4]])
+    assert_match_at("(?i:xssy)", "x\u017fSy", [[0, 4]])
+    assert_match_at("(?i:xssy)", "xs\u017fy", [[0, 4]])
+    assert_match_at("(?i:xssy)", "x\u00dfy", [[0, 3]])
+    assert_match_at("(?i:xssy)", "x\u1e9ey", [[0, 3]])
+    assert_match_at("(?i:\u00df)", "ss", [[0, 2]])
+    assert_match_at("(?i:\u00df)", "SS", [[0, 2]])
+    assert_match_at("(?i:[\u00df])", "ss", [[0, 2]])
+    assert_match_at("(?i:[\u00df])", "SS", [[0, 2]])
+    assert_match_at("(?i)(?<!ss)\u2728", "qq\u2728", [[2, 3]])     # Issue #92
+    assert_match_at("(?i)(?<!xss)\u2728", "qq\u2728", [[2, 3]])
+  end
+
   def test_options_in_look_behind
     assert_nothing_raised {
       assert_match_at("(?<=(?i)ab)cd", "ABcd", [[2,4]])