Instead of blindly trusting the first byte, decode UTF-8 safely.

LICENSE

@@ -18,6 +18,10 @@ released under the following license:
 rgbfix was rewritten from scratch by Anthony J. Bentley, and is released
 under the ISC license; see the source file for the text of the license.
 
+The UTF-8 decoder in src/asm/charmap.c was written by Björn Höhrmann and is
+released under the MIT license. The remainder of charmap.c was written by
+stag019, and is released under the ISC license.
+
 extern/err.c is derived from the Musl C library, http://www.musl-libc.org,
 and is released under the MIT license.
 

src/asm/charmap.c

@@ -1,3 +1,57 @@
+/*
+ * UTF-8 decoder copyright © 2008–2009 Björn Höhrmann <bjoern@hoehrmann.de>
+ * http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <stdint.h>
+
+static const uint8_t utf8d[] = {
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 00..1f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 20..3f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 40..5f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 60..7f
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9, // 80..9f
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, // a0..bf
+  8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // c0..df
+  0xa,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x4,0x3,0x3, // e0..ef
+  0xb,0x6,0x6,0x6,0x5,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8, // f0..ff
+  0x0,0x1,0x2,0x3,0x5,0x8,0x7,0x1,0x1,0x1,0x4,0x6,0x1,0x1,0x1,0x1, // s0..s0
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,1,1, // s1..s2
+  1,2,1,1,1,1,1,2,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1, // s3..s4
+  1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,3,1,3,1,1,1,1,1,1, // s5..s6
+  1,3,1,1,1,1,1,3,1,3,1,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // s7..s8
+};
+
+uint32_t
+decode(uint32_t* state, uint32_t* codep, uint32_t byte) {
+  uint32_t type = utf8d[byte];
+
+  *codep = (*state != 0) ?
+    (byte & 0x3fu) | (*codep << 6) :
+    (0xff >> type) & (byte);
+
+  *state = utf8d[256 + *state*16 + type];
+  return *state;
+}
+
 /*
  * Copyright © 2013 stag019 <stag019@gmail.com>
  *
@@ -28,30 +82,26 @@ struct Charmap globalCharmap = {0};
 extern struct Section *pCurrentSection;
 
 int
-readUTF8Char(char *destination, char *source)
+readUTF8Char(char *dest, char *src)
 {
-	int size;
+	uint32_t state;
-	UBYTE first;
+	uint32_t codep;
-	first = source[0];
+	int i;
 
-	if (first >= 0xFC) {
+	for (i = 0, state = 0;; i++) {
-		size = 6;
+		if (decode(&state, &codep, (uint8_t)src[i]) == 1) {
-	} else if (first >= 0xF8) {
+			fatalerror("invalid UTF-8 character");
-		size = 5;
+		}
-	} else if (first >= 0xF0) {
+
-		size = 4;
+		dest[i] = src[i];
-	} else if (first >= 0xE0) {
+
-		size = 3;
+		i++;
-	} else if (first >= 0xC0) {
+		if (state == 0) {
-		size = 2;
+			dest[i] = '\0';
-	} else if (first != '\0') {
+			return i;
-		size = 1;
+		}
-	} else {
+		dest[i] = src[i];
-		size = 0;
 	}
-	strncpy(destination, source, size);
-	destination[size] = 0;
-	return size;
 }
 
 int