xC: fix displaying IRC colours above 16

First, we indexed the colour array without a required offset.
Second, the data type was too small and overflowed negative.

Detected during a refactor, which this is a part of.

2 files changed, 27 insertions, 39 deletions

diff --git a/NEWS b/NEWS
index 9edef71..2ce6791 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,8 @@
 
  * xC: made message autosplitting respect text formatting
 
+ * xC: fixed displaying IRC colours above 16
+
 
 1.3.0 (2021-08-07) "New World Order"
 
diff --git a/xC.c b/xC.c
index 2b2bf73..e714c65 100644
--- a/xC.c
+++ b/xC.c
@@ -3191,7 +3191,7 @@ static const int g_mirc_to_terminal[] =
 
 // https://modern.ircdocs.horse/formatting.html
 // http://anti.teamidiot.de/static/nei/*/extended_mirc_color_proposal.html
-static const char g_extra_to_256[100 - 16] =
+static const int16_t g_extra_to_256[100 - 16] =
 {
 	 52,  94, 100,  58,  22,  29,  23,  24,  17,  54,  53,  89,
 	 88, 130, 142,  64,  28,  35,  30,  25,  18,  91,  90, 125,
@@ -3203,36 +3203,45 @@ static const char g_extra_to_256[100 - 16] =
 };
 
 static const char *
-formatter_parse_mirc_color (struct formatter *self, const char *s)
+irc_parse_mirc_color (const char *s, uint8_t *fg, uint8_t *bg)
 {
 	if (!isdigit_ascii (*s))
 	{
-		FORMATTER_ADD_ITEM (self, FG_COLOR, .color = -1);
-		FORMATTER_ADD_ITEM (self, BG_COLOR, .color = -1);
+		*fg = *bg = 99;
 		return s;
 	}
 
-	int fg = *s++ - '0';
+	*fg = *s++ - '0';
 	if (isdigit_ascii (*s))
-		fg = fg * 10 + (*s++ - '0');
-	if (fg < 16)
-		FORMATTER_ADD_ITEM (self, FG_COLOR, .color = g_mirc_to_terminal[fg]);
-	else
-		FORMATTER_ADD_ITEM (self, FG_COLOR,
-			.color = COLOR_256 (DEFAULT, g_extra_to_256[fg]));
+		*fg = *fg * 10 + (*s++ - '0');
 
 	if (*s != ',' || !isdigit_ascii (s[1]))
 		return s;
 	s++;
 
-	int bg = *s++ - '0';
+	*bg = *s++ - '0';
 	if (isdigit_ascii (*s))
-		bg = bg * 10 + (*s++ - '0');
+		*bg = *bg * 10 + (*s++ - '0');
+	return s;
+}
+
+static const char *
+formatter_parse_mirc_color (struct formatter *self, const char *s)
+{
+	uint8_t fg = 255, bg = 255;
+	s = irc_parse_mirc_color (s, &fg, &bg);
+
+	if (fg < 16)
+		FORMATTER_ADD_ITEM (self, FG_COLOR, .color = g_mirc_to_terminal[fg]);
+	else if (fg < 100)
+		FORMATTER_ADD_ITEM (self, FG_COLOR,
+			.color = COLOR_256 (DEFAULT, g_extra_to_256[fg - 16]));
+
 	if (bg < 16)
 		FORMATTER_ADD_ITEM (self, BG_COLOR, .color = g_mirc_to_terminal[bg]);
-	else
+	else if (bg < 100)
 		FORMATTER_ADD_ITEM (self, BG_COLOR,
-			.color = COLOR_256 (DEFAULT, g_extra_to_256[bg]));
+			.color = COLOR_256 (DEFAULT, g_extra_to_256[bg - 16]));
 
 	return s;
 }
@@ -8257,29 +8266,6 @@ irc_serialize_char_attrs (const struct irc_char_attrs *attrs, struct str *out)
 	if (attrs->attributes & TEXT_MONOSPACE)   str_append_c (out, '\x11');
 }
 
-static const char *
-irc_analyze_mirc_color (const char *s, uint8_t *fg, uint8_t *bg)
-{
-	if (!isdigit_ascii (*s))
-	{
-		*fg = *bg = 99;
-		return s;
-	}
-
-	*fg = *s++ - '0';
-	if (isdigit_ascii (*s))
-		*fg = *fg * 10 + (*s++ - '0');
-
-	if (*s != ',' || !isdigit_ascii (s[1]))
-		return s;
-	s++;
-
-	*bg = *s++ - '0';
-	if (isdigit_ascii (*s))
-		*bg = *bg * 10 + (*s++ - '0');
-	return s;
-}
-
 // The text needs to be NUL-terminated
 // TODO: try to deduplicate analogous code in formatter_parse_mirc()
 static struct irc_char_attrs *
@@ -8303,7 +8289,7 @@ irc_analyze_text (const char *text, size_t len)
 		case '\x16': next.attributes ^= TEXT_INVERSE;     break;
 
 		case '\x03':
-			text = irc_analyze_mirc_color (text, &next.fg, &next.bg);
+			text = irc_parse_mirc_color (text, &next.fg, &next.bg);
 			break;
 		case '\x0f':
 			next = blank;