diff --git a/ChangeLog b/ChangeLog
index 153c9e74e3..7749a19a4d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Jan 15 23:52:51 2008  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* enc/*: add ARG_UNUSED.
+
+	* enc/koi8_u.c: added.
+
 Tue Jan 15 23:00:08 2008  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* enc/utf_{16,32}{be,le}.c: remove some ARG_UNUSED.  replace struct
diff --git a/enc/big5.c b/enc/big5.c
index 5829c3c47f..676e262252 100644
--- a/enc/big5.c
+++ b/enc/big5.c
@@ -49,7 +49,7 @@ static const int EncLen_BIG5[] = {
 };
 
 static int
-big5_mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc)
+big5_mbc_enc_len(const UChar* p, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   return EncLen_BIG5[*p];
 }
@@ -135,7 +135,7 @@ big5_left_adjust_char_head(const UChar* start, const UChar* s, OnigEncoding enc)
 }
 
 static int
-big5_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc)
+big5_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   const UChar c = *s;
 
diff --git a/enc/euc_jp.c b/enc/euc_jp.c
index 7950f41d5d..1828d03a3d 100644
--- a/enc/euc_jp.c
+++ b/enc/euc_jp.c
@@ -115,7 +115,7 @@ static const signed char trans[][0x100] = {
 #undef F
 
 static int
-mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc)
+mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc ARG_UNUSED)
 {
   int firstbyte = *p++;
   state_t s;
@@ -151,7 +151,7 @@ mbc_to_code(const UChar* p, const UChar* end, OnigEncoding enc)
 }
 
 static int
-code_to_mbclen(OnigCodePoint code, OnigEncoding enc)
+code_to_mbclen(OnigCodePoint code, OnigEncoding enc ARG_UNUSED)
 {
   if (ONIGENC_IS_CODE_ASCII(code)) return 1;
   else if (code > 0xffffff) return 0;
@@ -241,7 +241,7 @@ left_adjust_char_head(const UChar* start, const UChar* s, OnigEncoding enc)
 }
 
 static int
-is_allowed_reverse_match(const UChar* s, const UChar* end, OnigEncoding enc)
+is_allowed_reverse_match(const UChar* s, const UChar* end, OnigEncoding enc ARG_UNUSED)
 {
   const UChar c = *s;
   if (c <= 0x7e || c == 0x8e || c == 0x8f)
@@ -297,7 +297,7 @@ property_name_to_ctype(OnigEncoding enc, UChar* p, UChar* end)
 }
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (ctype <= ONIGENC_MAX_STD_CTYPE) {
     if (code < 128)
@@ -323,7 +323,7 @@ is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
 
 static int
 get_ctype_code_range(OnigCtype ctype, OnigCodePoint* sb_out,
-		     const OnigCodePoint* ranges[], OnigEncoding enc)
+		     const OnigCodePoint* ranges[], OnigEncoding enc ARG_UNUSED)
 {
   if (ctype <= ONIGENC_MAX_STD_CTYPE) {
     return ONIG_NO_SUPPORT_CONFIG;
diff --git a/enc/euc_kr.c b/enc/euc_kr.c
index 0b42f9985d..09869e6b5a 100644
--- a/enc/euc_kr.c
+++ b/enc/euc_kr.c
@@ -49,7 +49,7 @@ static const int EncLen_EUCKR[] = {
 };
 
 static int
-euckr_mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc)
+euckr_mbc_enc_len(const UChar* p, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   return EncLen_EUCKR[*p];
 }
@@ -111,7 +111,7 @@ euckr_left_adjust_char_head(const UChar* start, const UChar* s, OnigEncoding enc
 }
 
 static int
-euckr_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc)
+euckr_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   const UChar c = *s;
   if (c <= 0x7e) return TRUE;
diff --git a/enc/euc_tw.c b/enc/euc_tw.c
index 395f1e9ae0..8638021cc1 100644
--- a/enc/euc_tw.c
+++ b/enc/euc_tw.c
@@ -49,13 +49,13 @@ static const int EncLen_EUCTW[] = {
 };
 
 static int
-euctw_mbc_enc_len(const UChar* p, const UChar* end, OnigEncoding enc)
+euctw_mbc_enc_len(const UChar* p, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   return EncLen_EUCTW[*p];
 }
 
 static OnigCodePoint
-euctw_mbc_to_code(const UChar* p, const UChar* end, OnigEncoding enc)
+euctw_mbc_to_code(const UChar* p, const UChar* end, OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_mbn_mbc_to_code(enc, p, end);
 }
@@ -111,7 +111,7 @@ euctw_left_adjust_char_head(const UChar* start, const UChar* s, OnigEncoding enc
 }
 
 static int
-euctw_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc)
+euctw_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   const UChar c = *s;
   if (c <= 0x7e) return TRUE;
diff --git a/enc/gb18030.c b/enc/gb18030.c
index 100c2bb78e..b2adb785f8 100644
--- a/enc/gb18030.c
+++ b/enc/gb18030.c
@@ -63,7 +63,7 @@ static const char GB18030_MAP[] = {
 };
 
 static int
-gb18030_mbc_enc_len(const UChar* p, const UChar* end, OnigEncoding enc)
+gb18030_mbc_enc_len(const UChar* p, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   if (GB18030_MAP[*p] != CM)
     return 1;
@@ -470,7 +470,7 @@ gb18030_left_adjust_char_head(const UChar* start, const UChar* s, OnigEncoding e
 }
 
 static int
-gb18030_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc)
+gb18030_is_allowed_reverse_match(const UChar* s, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
 {
   return GB18030_MAP[*s] == C1 ? TRUE : FALSE;
 }
diff --git a/enc/iso_8859_1.c b/enc/iso_8859_1.c
index 10c68f5300..e2779753e2 100644
--- a/enc/iso_8859_1.c
+++ b/enc/iso_8859_1.c
@@ -104,7 +104,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 		    OnigApplyAllCaseFoldFunc f, void* arg,
-		    OnigEncoding enc)
+		    OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
             sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -115,7 +115,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 			   const OnigUChar* p, const OnigUChar* end,
 			   OnigCaseFoldCodeItem items[],
-			   OnigEncoding enc)
+			   OnigEncoding enc ARG_UNUSED)
 {
   if (0x41 <= *p && *p <= 0x5a) {
     items[0].byte_len = 1;
@@ -201,8 +201,8 @@ get_case_fold_codes_by_str(OnigCaseFoldType flag,
 }
 
 static int
-mbc_case_fold(OnigCaseFoldType flag, const UChar** pp, const UChar* end,
-	      UChar* lower, OnigEncoding enc)
+mbc_case_fold(OnigCaseFoldType flag, const UChar** pp, const UChar* end ARG_UNUSED,
+	      UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -246,7 +246,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag,
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_1_CTYPE(code, ctype);
diff --git a/enc/iso_8859_10.c b/enc/iso_8859_10.c
index 64ec45a3b8..2089a92df0 100644
--- a/enc/iso_8859_10.c
+++ b/enc/iso_8859_10.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_10_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-			  const UChar** pp, const UChar* end, UChar* lower,
-			  OnigEncoding enc)
+			  const UChar** pp, const UChar* end ARG_UNUSED,
+			  UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -145,7 +145,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_10_CTYPE(code, ctype);
@@ -205,7 +205,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 			       OnigApplyAllCaseFoldFunc f, void* arg,
-			       OnigEncoding enc)
+			       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -216,7 +216,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 				       const OnigUChar* p, const OnigUChar* end,
 				       OnigCaseFoldCodeItem items[],
-				       OnigEncoding enc)
+				       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_11.c b/enc/iso_8859_11.c
index edba3cb0b1..facb28437d 100644
--- a/enc/iso_8859_11.c
+++ b/enc/iso_8859_11.c
@@ -68,7 +68,7 @@ static const unsigned short EncISO_8859_11_CtypeTable[256] = {
 };
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_11_CTYPE(code, ctype);
diff --git a/enc/iso_8859_13.c b/enc/iso_8859_13.c
index 9f7f12122d..cbb79d9337 100644
--- a/enc/iso_8859_13.c
+++ b/enc/iso_8859_13.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_13_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-			  const UChar** pp, const UChar* end, UChar* lower,
-			  OnigEncoding enc)
+			  const UChar** pp, const UChar* end ARG_UNUSED,
+			  UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -149,7 +149,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_13_CTYPE(code, ctype);
@@ -194,7 +194,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 				OnigApplyAllCaseFoldFunc f, void* arg,
-				OnigEncoding enc)
+				OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -205,7 +205,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 				       const OnigUChar* p, const OnigUChar* end,
 				       OnigCaseFoldCodeItem items[],
-				       OnigEncoding enc)
+				       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_14.c b/enc/iso_8859_14.c
index 0970145dc1..d508848208 100644
--- a/enc/iso_8859_14.c
+++ b/enc/iso_8859_14.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_14_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-                          const UChar** pp, const UChar* end, UChar* lower,
-			  OnigEncoding enc)
+			  const UChar** pp, const UChar* end ARG_UNUSED,
+			  UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -146,7 +146,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag,
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_14_CTYPE(code, ctype);
@@ -207,7 +207,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 				OnigApplyAllCaseFoldFunc f, void* arg,
-				OnigEncoding enc)
+				OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -218,7 +218,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 				       const OnigUChar* p, const OnigUChar* end,
 				       OnigCaseFoldCodeItem items[],
-				       OnigEncoding enc)
+				       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_15.c b/enc/iso_8859_15.c
index a842ab4f3d..f7c5bbeef1 100644
--- a/enc/iso_8859_15.c
+++ b/enc/iso_8859_15.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_15_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-			  const UChar** pp, const UChar* end, UChar* lower,
-			  OnigEncoding enc)
+			  const UChar** pp, const UChar* end ARG_UNUSED,
+			  UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -150,7 +150,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag,
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_15_CTYPE(code, ctype);
@@ -201,7 +201,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 				OnigApplyAllCaseFoldFunc f, void* arg,
-				OnigEncoding enc)
+				OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -212,7 +212,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 				       const OnigUChar* p, const OnigUChar* end,
 				       OnigCaseFoldCodeItem items[],
-				       OnigEncoding enc)
+				       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_16.c b/enc/iso_8859_16.c
index 86e626c5fb..61e9c28464 100644
--- a/enc/iso_8859_16.c
+++ b/enc/iso_8859_16.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_16_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-			  const UChar** pp, const UChar* end, UChar* lower,
-			  OnigEncoding enc)
+			  const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+			  OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -145,7 +145,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_16_CTYPE(code, ctype);
@@ -203,7 +203,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 				OnigApplyAllCaseFoldFunc f, void* arg,
-				OnigEncoding enc)
+				OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -214,7 +214,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 				       const OnigUChar* p, const OnigUChar* end,
 				       OnigCaseFoldCodeItem items[],
-				       OnigEncoding enc)
+				       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_2.c b/enc/iso_8859_2.c
index a6a6c3d4c1..8f4e1ad2f8 100644
--- a/enc/iso_8859_2.c
+++ b/enc/iso_8859_2.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_2_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-	      const UChar** pp, const UChar* end, UChar* lower,
-	      OnigEncoding enc)
+	      const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+	      OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -192,7 +192,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 		    OnigApplyAllCaseFoldFunc f, void* arg,
-		    OnigEncoding enc)
+		    OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
             sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -203,7 +203,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 			   const OnigUChar* p, const OnigUChar* end,
 			   OnigCaseFoldCodeItem items[],
-			   OnigEncoding enc)
+			   OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -211,7 +211,7 @@ get_case_fold_codes_by_str(OnigCaseFoldType flag,
 }
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_2_CTYPE(code, ctype);
diff --git a/enc/iso_8859_3.c b/enc/iso_8859_3.c
index 5b0ba04c73..f484061aa4 100644
--- a/enc/iso_8859_3.c
+++ b/enc/iso_8859_3.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_3_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-	      const UChar** pp, const UChar* end, UChar* lower,
-	      OnigEncoding enc)
+	      const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+	      OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -149,7 +149,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_3_CTYPE(code, ctype);
@@ -201,7 +201,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 		    OnigApplyAllCaseFoldFunc f, void* arg,
-		    OnigEncoding enc)
+		    OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -212,7 +212,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 			   const OnigUChar* p, const OnigUChar* end,
 			   OnigCaseFoldCodeItem items[],
-			   OnigEncoding enc)
+			   OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_4.c b/enc/iso_8859_4.c
index d9d41f4e53..f548ed581d 100644
--- a/enc/iso_8859_4.c
+++ b/enc/iso_8859_4.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_4_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-	      const UChar** pp, const UChar* end, UChar* lower,
-	      OnigEncoding enc)
+	      const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+	      OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -148,7 +148,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_4_CTYPE(code, ctype);
@@ -203,7 +203,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 		    OnigApplyAllCaseFoldFunc f, void* arg,
-		    OnigEncoding enc)
+		    OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -214,7 +214,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 			   const OnigUChar* p, const OnigUChar* end,
 			   OnigCaseFoldCodeItem items[],
-			   OnigEncoding enc)
+			   OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/iso_8859_5.c b/enc/iso_8859_5.c
index d53cbdbe71..7eb78d2b0b 100644
--- a/enc/iso_8859_5.c
+++ b/enc/iso_8859_5.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_5_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-	      const UChar** pp, const UChar* end, UChar* lower,
-	      OnigEncoding enc)
+	      const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+	      OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -129,7 +129,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_5_CTYPE(code, ctype);
@@ -191,7 +191,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 		    OnigApplyAllCaseFoldFunc f, void* arg,
-		    OnigEncoding enc)
+		    OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
@@ -202,7 +202,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 			   const OnigUChar* p, const OnigUChar* end,
 			   OnigCaseFoldCodeItem items[],
-			   OnigEncoding enc)
+			   OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
diff --git a/enc/iso_8859_6.c b/enc/iso_8859_6.c
index 8a91280c1c..0f9a1b7d95 100644
--- a/enc/iso_8859_6.c
+++ b/enc/iso_8859_6.c
@@ -68,7 +68,7 @@ static const unsigned short EncISO_8859_6_CtypeTable[256] = {
 };
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_6_CTYPE(code, ctype);
diff --git a/enc/iso_8859_7.c b/enc/iso_8859_7.c
index 68d590dfa1..4b1f6167c2 100644
--- a/enc/iso_8859_7.c
+++ b/enc/iso_8859_7.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_7_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-	      const UChar** pp, const UChar* end, UChar* lower,
-	      OnigEncoding enc)
+	      const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+	      OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -137,7 +137,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag,
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_7_CTYPE(code, ctype);
@@ -187,7 +187,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 		    OnigApplyAllCaseFoldFunc f, void* arg,
-		    OnigEncoding enc)
+		    OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
@@ -198,7 +198,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 			   const OnigUChar* p, const OnigUChar* end,
 			   OnigCaseFoldCodeItem items[],
-			   OnigEncoding enc)
+			   OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
diff --git a/enc/iso_8859_8.c b/enc/iso_8859_8.c
index 72cfea95d7..ab58084461 100644
--- a/enc/iso_8859_8.c
+++ b/enc/iso_8859_8.c
@@ -68,7 +68,7 @@ static const unsigned short EncISO_8859_8_CtypeTable[256] = {
 };
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_8_CTYPE(code, ctype);
diff --git a/enc/iso_8859_9.c b/enc/iso_8859_9.c
index 0af43fb733..9c228ad93e 100644
--- a/enc/iso_8859_9.c
+++ b/enc/iso_8859_9.c
@@ -105,8 +105,8 @@ static const unsigned short EncISO_8859_9_CtypeTable[256] = {
 
 static int
 mbc_case_fold(OnigCaseFoldType flag,
-	      const UChar** pp, const UChar* end, UChar* lower,
-	      OnigEncoding enc)
+	      const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower,
+	      OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -149,7 +149,7 @@ is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end)
 #endif
 
 static int
-is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_ISO_8859_9_CTYPE(code, ctype);
@@ -194,7 +194,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 static int
 apply_all_case_fold(OnigCaseFoldType flag,
 			       OnigApplyAllCaseFoldFunc f, void* arg,
-			       OnigEncoding enc)
+			       OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
@@ -205,7 +205,7 @@ static int
 get_case_fold_codes_by_str(OnigCaseFoldType flag,
 				      const OnigUChar* p, const OnigUChar* end,
 				      OnigCaseFoldCodeItem items[],
-				      OnigEncoding enc)
+				      OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 1,
diff --git a/enc/koi8_r.c b/enc/koi8_r.c
index 88fa04eaae..dfdf6d248a 100644
--- a/enc/koi8_r.c
+++ b/enc/koi8_r.c
@@ -105,7 +105,8 @@ static const unsigned short EncKOI8_R_CtypeTable[256] = {
 
 static int
 koi8_r_mbc_case_fold(OnigCaseFoldType flag ARG_UNUSED,
-             const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower, OnigEncoding enc)
+		     const UChar** pp, const UChar* end ARG_UNUSED,
+		     UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -116,7 +117,8 @@ koi8_r_mbc_case_fold(OnigCaseFoldType flag ARG_UNUSED,
 
 #if 0
 static int
-koi8_r_is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* end, OnigEncoding enc)
+koi8_r_is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp,
+			const UChar* end, OnigEncoding enc ARG_UNUSED)
 {
   int v;
   const UChar* p = *pp;
@@ -128,7 +130,8 @@ koi8_r_is_mbc_ambiguous(OnigCaseFoldType flag, const UChar** pp, const UChar* en
 #endif
 
 static int
-koi8_r_is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+koi8_r_is_code_ctype(OnigCodePoint code, unsigned int ctype,
+		     OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_KOI8_R_CTYPE(code, ctype);
@@ -176,7 +179,8 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 
 static int
 koi8_r_apply_all_case_fold(OnigCaseFoldType flag,
-			       OnigApplyAllCaseFoldFunc f, void* arg, OnigEncoding enc)
+			   OnigApplyAllCaseFoldFunc f,
+			   void* arg, OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
@@ -185,7 +189,8 @@ koi8_r_apply_all_case_fold(OnigCaseFoldType flag,
 
 static int
 koi8_r_get_case_fold_codes_by_str(OnigCaseFoldType flag,
-    const OnigUChar* p, const OnigUChar* end, OnigCaseFoldCodeItem items[], OnigEncoding enc)
+		  const OnigUChar* p, const OnigUChar* end,
+		  OnigCaseFoldCodeItem items[], OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
diff --git a/enc/shift_jis.c b/enc/shift_jis.c
index 48e7842dd9..dd42ebee44 100644
--- a/enc/shift_jis.c
+++ b/enc/shift_jis.c
@@ -115,7 +115,7 @@ static const signed char trans[][0x100] = {
 #undef F
 
 static int
-mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc)
+mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc ARG_UNUSED)
 {
   int firstbyte = *p++;
   state_t s;
@@ -129,7 +129,7 @@ mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc)
 }
 
 static int
-code_to_mbclen(OnigCodePoint code, OnigEncoding enc)
+code_to_mbclen(OnigCodePoint code, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256) {
     if (EncLen_SJIS[(int )code] == 1)
@@ -252,7 +252,7 @@ left_adjust_char_head(const UChar* start, const UChar* s, OnigEncoding enc)
 }
 
 static int
-is_allowed_reverse_match(const UChar* s, const UChar* end, OnigEncoding enc)
+is_allowed_reverse_match(const UChar* s, const UChar* end, OnigEncoding enc ARG_UNUSED)
 {
   const UChar c = *s;
   return (SJIS_ISMB_TRAIL(c) ? FALSE : TRUE);
@@ -332,7 +332,7 @@ is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
 
 static int
 get_ctype_code_range(OnigCtype ctype, OnigCodePoint* sb_out,
-		     const OnigCodePoint* ranges[], OnigEncoding enc)
+		     const OnigCodePoint* ranges[], OnigEncoding enc ARG_UNUSED)
 {
   if (ctype <= ONIGENC_MAX_STD_CTYPE) {
     return ONIG_NO_SUPPORT_CONFIG;
diff --git a/enc/windows_1251.c b/enc/windows_1251.c
index faba0c937b..5317b3da6c 100644
--- a/enc/windows_1251.c
+++ b/enc/windows_1251.c
@@ -106,7 +106,7 @@ static const unsigned short EncCP1251_CtypeTable[256] = {
 
 static int
 cp1251_mbc_case_fold(OnigCaseFoldType flag ARG_UNUSED,
-             const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower, OnigEncoding enc)
+             const UChar** pp, const UChar* end ARG_UNUSED, UChar* lower, OnigEncoding enc ARG_UNUSED)
 {
   const UChar* p = *pp;
 
@@ -116,7 +116,7 @@ cp1251_mbc_case_fold(OnigCaseFoldType flag ARG_UNUSED,
 }
 
 static int
-cp1251_is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc)
+cp1251_is_code_ctype(OnigCodePoint code, unsigned int ctype, OnigEncoding enc ARG_UNUSED)
 {
   if (code < 256)
     return ENC_IS_CP1251_CTYPE(code, ctype);
@@ -164,7 +164,7 @@ static const OnigPairCaseFoldCodes CaseFoldMap[] = {
 
 static int
 cp1251_apply_all_case_fold(OnigCaseFoldType flag,
-			       OnigApplyAllCaseFoldFunc f, void* arg, OnigEncoding enc)
+			       OnigApplyAllCaseFoldFunc f, void* arg, OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_apply_all_case_fold_with_map(
              sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,
@@ -173,7 +173,7 @@ cp1251_apply_all_case_fold(OnigCaseFoldType flag,
 
 static int
 cp1251_get_case_fold_codes_by_str(OnigCaseFoldType flag,
-    const OnigUChar* p, const OnigUChar* end, OnigCaseFoldCodeItem items[], OnigEncoding enc)
+    const OnigUChar* p, const OnigUChar* end, OnigCaseFoldCodeItem items[], OnigEncoding enc ARG_UNUSED)
 {
   return onigenc_get_case_fold_codes_by_str_with_map(
 	     sizeof(CaseFoldMap)/sizeof(OnigPairCaseFoldCodes), CaseFoldMap, 0,