From 3df8017e9b7ea2b72477294133563b4ff304a007 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Tue, 17 May 2022 17:29:39 -0600
Subject: [PATCH] [ot-tag] Optimize subtag_matches() more

---
 src/gen-tag-table.py   |   2 +-
 src/hb-ot-tag-table.hh | 112 ++++++++++++++++++++---------------------
 src/hb-ot-tag.cc       |   5 +-
 3 files changed, 59 insertions(+), 60 deletions(-)

diff --git a/src/gen-tag-table.py b/src/gen-tag-table.py
index 9fc3c59fd..d8c5a2fcf 100755
--- a/src/gen-tag-table.py
+++ b/src/gen-tag-table.py
@@ -999,7 +999,7 @@ def print_subtag_matches (subtag, new_line):
 		if new_line:
 			print ()
 			print ('\t&& ', end='')
-		print ('subtag_matches (lang_str, limit, "-%s")' % subtag, end='')
+		print ('subtag_matches (lang_str, limit, "-%s", %i)' % (subtag, 1 + len (subtag)), end='')
 
 complex_tags = collections.defaultdict (list)
 for initial, group in itertools.groupby ((lt_tags for lt_tags in [
diff --git a/src/hb-ot-tag-table.hh b/src/hb-ot-tag-table.hh
index 341eb20ce..bcf40123a 100644
--- a/src/hb-ot-tag-table.hh
+++ b/src/hb-ot-tag-table.hh
@@ -1645,63 +1645,63 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
   if (limit - lang_str > 5 ||
       (limit - lang_str == 5 && *lang_str == '-'))
   {
-    if (subtag_matches (lang_str, limit, "-fonnapa"))
+    if (subtag_matches (lang_str, limit, "-fonnapa", 8))
     {
       /* Undetermined; North American Phonetic Alphabet */
       tags[0] = HB_TAG('A','P','P','H');  /* Phonetic transcription—Americanist conventions */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-polyton"))
+    if (subtag_matches (lang_str, limit, "-polyton", 8))
     {
       /* Modern Greek (1453-); Polytonic Greek */
       tags[0] = HB_TAG('P','G','R',' ');  /* Polytonic Greek */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-arevmda"))
+    if (subtag_matches (lang_str, limit, "-arevmda", 8))
     {
       /* Armenian; Western Armenian (retired code) */
       tags[0] = HB_TAG('H','Y','E',' ');  /* Armenian */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-provenc"))
+    if (subtag_matches (lang_str, limit, "-provenc", 8))
     {
       /* Occitan (post 1500); Provençal */
       tags[0] = HB_TAG('P','R','O',' ');  /* Provençal / Old Provençal */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-fonipa"))
+    if (subtag_matches (lang_str, limit, "-fonipa", 7))
     {
       /* Undetermined; International Phonetic Alphabet */
       tags[0] = HB_TAG('I','P','P','H');  /* Phonetic transcription—IPA conventions */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-geok"))
+    if (subtag_matches (lang_str, limit, "-geok", 5))
     {
       /* Undetermined; Khutsuri (Asomtavruli and Nuskhuri) */
       tags[0] = HB_TAG('K','G','E',' ');  /* Khutsuri Georgian */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-syre"))
+    if (subtag_matches (lang_str, limit, "-syre", 5))
     {
       /* Undetermined; Syriac (Estrangelo variant) */
       tags[0] = HB_TAG('S','Y','R','E');  /* Syriac, Estrangela script-variant (equivalent to ISO 15924 'Syre') */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-syrj"))
+    if (subtag_matches (lang_str, limit, "-syrj", 5))
     {
       /* Undetermined; Syriac (Western variant) */
       tags[0] = HB_TAG('S','Y','R','J');  /* Syriac, Western script-variant (equivalent to ISO 15924 'Syrj') */
       *count = 1;
       return true;
     }
-    if (subtag_matches (lang_str, limit, "-syrn"))
+    if (subtag_matches (lang_str, limit, "-syrn", 5))
     {
       /* Undetermined; Syriac (Eastern variant) */
       tags[0] = HB_TAG('S','Y','R','N');  /* Syriac, Eastern script-variant (equivalent to ISO 15924 'Syrn') */
@@ -1994,7 +1994,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "do-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Min Dong Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2002,7 +2002,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "do-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Min Dong Chinese; Macao */
       unsigned int i;
@@ -2016,7 +2016,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "do-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Min Dong Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2024,7 +2024,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "jy-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Jinyu Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2032,7 +2032,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "jy-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Jinyu Chinese; Macao */
       unsigned int i;
@@ -2046,7 +2046,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "jy-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Jinyu Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2054,7 +2054,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "mn-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Mandarin Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2062,7 +2062,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "mn-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Mandarin Chinese; Macao */
       unsigned int i;
@@ -2076,7 +2076,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "mn-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Mandarin Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2084,7 +2084,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "np-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Northern Ping Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2092,7 +2092,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "np-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Northern Ping Chinese; Macao */
       unsigned int i;
@@ -2106,7 +2106,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "np-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Northern Ping Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2114,7 +2114,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "px-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Pu-Xian Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2122,7 +2122,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "px-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Pu-Xian Chinese; Macao */
       unsigned int i;
@@ -2136,7 +2136,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "px-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Pu-Xian Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2144,7 +2144,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "sp-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Southern Ping Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2152,7 +2152,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "sp-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Southern Ping Chinese; Macao */
       unsigned int i;
@@ -2166,7 +2166,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "sp-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Southern Ping Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2174,7 +2174,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "zh-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Huizhou Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2182,7 +2182,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "zh-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Huizhou Chinese; Macao */
       unsigned int i;
@@ -2196,7 +2196,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "zh-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Huizhou Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2204,7 +2204,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "zo-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Min Zhong Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2212,7 +2212,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "zo-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Min Zhong Chinese; Macao */
       unsigned int i;
@@ -2226,7 +2226,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "zo-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Min Zhong Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2277,7 +2277,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "an-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Gan Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2285,7 +2285,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "an-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Gan Chinese; Macao */
       unsigned int i;
@@ -2299,7 +2299,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "an-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Gan Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2377,7 +2377,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "ak-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Hakka Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2385,7 +2385,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "ak-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Hakka Chinese; Macao */
       unsigned int i;
@@ -2399,7 +2399,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "ak-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Hakka Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2407,7 +2407,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "sn-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Xiang Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2415,7 +2415,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "sn-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Xiang Chinese; Macao */
       unsigned int i;
@@ -2429,7 +2429,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "sn-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Xiang Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2511,7 +2511,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "np-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Min Bei Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2519,7 +2519,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "np-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Min Bei Chinese; Macao */
       unsigned int i;
@@ -2533,7 +2533,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "np-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Min Bei Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2541,7 +2541,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "nw-", 3)
-	&& subtag_matches (lang_str, limit, "-th"))
+	&& subtag_matches (lang_str, limit, "-th", 3))
     {
       /* Mon; Thailand */
       tags[0] = HB_TAG('M','O','N','T');  /* Thailand Mon */
@@ -2585,7 +2585,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "an-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Min Nan Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2593,7 +2593,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "an-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Min Nan Chinese; Macao */
       unsigned int i;
@@ -2607,7 +2607,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "an-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Min Nan Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2631,7 +2631,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
     break;
   case 'r':
     if (0 == strncmp (&lang_str[1], "o-", 2)
-	&& subtag_matches (lang_str, limit, "-md"))
+	&& subtag_matches (lang_str, limit, "-md", 3))
     {
       /* Romanian; Moldova */
       unsigned int i;
@@ -2681,7 +2681,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "uu-", 3)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Wu Chinese; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2689,7 +2689,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "uu-", 3)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Wu Chinese; Macao */
       unsigned int i;
@@ -2703,7 +2703,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "uu-", 3)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Wu Chinese; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
@@ -2770,7 +2770,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "h-", 2)
-	&& subtag_matches (lang_str, limit, "-hk"))
+	&& subtag_matches (lang_str, limit, "-hk", 3))
     {
       /* Chinese [macrolanguage]; Hong Kong */
       tags[0] = HB_TAG('Z','H','H',' ');  /* Chinese, Traditional, Hong Kong SAR */
@@ -2778,7 +2778,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "h-", 2)
-	&& subtag_matches (lang_str, limit, "-mo"))
+	&& subtag_matches (lang_str, limit, "-mo", 3))
     {
       /* Chinese [macrolanguage]; Macao */
       unsigned int i;
@@ -2792,7 +2792,7 @@ hb_ot_tags_from_complex_language (const char   *lang_str,
       return true;
     }
     if (0 == strncmp (&lang_str[1], "h-", 2)
-	&& subtag_matches (lang_str, limit, "-tw"))
+	&& subtag_matches (lang_str, limit, "-tw", 3))
     {
       /* Chinese [macrolanguage]; Taiwan, Province of China */
       tags[0] = HB_TAG('Z','H','T',' ');  /* Chinese, Traditional */
diff --git a/src/hb-ot-tag.cc b/src/hb-ot-tag.cc
index 8d63eb791..31f247cf4 100644
--- a/src/hb-ot-tag.cc
+++ b/src/hb-ot-tag.cc
@@ -192,10 +192,9 @@ hb_ot_tag_to_script (hb_tag_t tag)
 static inline bool
 subtag_matches (const char *lang_str,
 		const char *limit,
-		const char *subtag)
+		const char *subtag,
+		unsigned subtag_len)
 {
-  unsigned subtag_len = strlen (subtag);
-
   if (likely ((unsigned) (limit - lang_str) < subtag_len))
     return false;