overhaul utf8decode()

this changes the utf8decode function to:

* report when an error occurs
* report how many bytes to advance on error

these will be useful in the next commit to render invalid utf8
sequences.

the new implementation is also shorter and more direct.

drw.c

@@ -9,54 +9,40 @@
 #include "util.h"
 
 #define UTF_INVALID 0xFFFD
-#define UTF_SIZ     4
 
-static const unsigned char utfbyte[UTF_SIZ + 1] = {0x80,    0, 0xC0, 0xE0, 0xF0};
+static int
-static const unsigned char utfmask[UTF_SIZ + 1] = {0xC0, 0x80, 0xE0, 0xF0, 0xF8};
+utf8decode(const char *s_in, long *u, int *err)
-static const long utfmin[UTF_SIZ + 1] = {       0,    0,  0x80,  0x800,  0x10000};
-static const long utfmax[UTF_SIZ + 1] = {0x10FFFF, 0x7F, 0x7FF, 0xFFFF, 0x10FFFF};
-
-static long
-utf8decodebyte(const char c, size_t *i)
 {
-	for (*i = 0; *i < (UTF_SIZ + 1); ++(*i))
+	static const unsigned char lens[] = {
-		if (((unsigned char)c & utfmask[*i]) == utfbyte[*i])
+		/* 0XXXX */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-			return (unsigned char)c & ~utfmask[*i];
+		/* 10XXX */ 0, 0, 0, 0, 0, 0, 0, 0,  /* invalid */
-	return 0;
+		/* 110XX */ 2, 2, 2, 2,
-}
+		/* 1110X */ 3, 3,
+		/* 11110 */ 4,
+		/* 11111 */ 0,  /* invalid */
+	};
+	static const unsigned char leading_mask[] = { 0x7F, 0x1F, 0x0F, 0x07 };
+	static const unsigned int overlong[] = { 0x0, 0x80, 0x0800, 0x10000 };
 
-static size_t
+	const unsigned char *s = (const unsigned char *)s_in;
-utf8validate(long *u, size_t i)
+	int len = lens[*s >> 3];
-{
-	if (!BETWEEN(*u, utfmin[i], utfmax[i]) || BETWEEN(*u, 0xD800, 0xDFFF))
 	*u = UTF_INVALID;
-	for (i = 1; *u > utfmax[i]; ++i)
+	*err = 1;
-		;
+	if (len == 0)
-	return i;
-}
-
-static size_t
-utf8decode(const char *c, long *u, size_t clen)
-{
-	size_t i, j, len, type;
-	long udecoded;
-
-	*u = UTF_INVALID;
-	if (!clen)
-		return 0;
-	udecoded = utf8decodebyte(c[0], &len);
-	if (!BETWEEN(len, 1, UTF_SIZ))
 		return 1;
-	for (i = 1, j = 1; i < clen && j < len; ++i, ++j) {
-		udecoded = (udecoded << 6) | utf8decodebyte(c[i], &type);
-		if (type)
-			return j;
-	}
-	if (j < len)
-		return 0;
-	*u = udecoded;
-	utf8validate(u, len);
 
+	long cp = s[0] & leading_mask[len - 1];
+	for (int i = 1; i < len; ++i) {
+		if (s[i] == '\0' || (s[i] & 0xC0) != 0x80)
+			return i;
+		cp = (cp << 6) | (s[i] & 0x3F);
+	}
+	/* out of range, surrogate, overlong encoding */
+	if (cp > 0x10FFFF || (cp >> 11) == 0x1B || cp < overlong[len - 1])
+		return len;
+
+	*err = 0;
+	*u = cp;
 	return len;
 }
 
@@ -242,7 +228,7 @@ drw_text(Drw *drw, int x, int y, unsigned int w, unsigned int h, unsigned int lp
 	unsigned int tmpw, ew, ellipsis_w = 0, ellipsis_len, hash, h0, h1;
 	XftDraw *d = NULL;
 	Fnt *usedfont, *curfont, *nextfont;
-	int utf8strlen, utf8charlen, render = x || y || w || h;
+	int utf8strlen, utf8charlen, utf8err, render = x || y || w || h;
 	long utf8codepoint = 0;
 	const char *utf8str;
 	FcCharSet *fccharset;
@@ -272,11 +258,11 @@ drw_text(Drw *drw, int x, int y, unsigned int w, unsigned int h, unsigned int lp
 	if (!ellipsis_width && render)
 		ellipsis_width = drw_fontset_getwidth(drw, "...");
 	while (1) {
-		ew = ellipsis_len = utf8strlen = 0;
+		ew = ellipsis_len = utf8err = utf8charlen = utf8strlen = 0;
 		utf8str = text;
 		nextfont = NULL;
 		while (*text) {
-			utf8charlen = utf8decode(text, &utf8codepoint, UTF_SIZ);
+			utf8charlen = utf8decode(text, &utf8codepoint, &utf8err);
 			for (curfont = drw->fonts; curfont; curfont = curfont->next) {
 				charexists = charexists || XftCharExists(drw->dpy, curfont->xfont, utf8codepoint);
 				if (charexists) {