From 3e1705c5c059ecad3c90b785f4d364c8ecfd45c1 Mon Sep 17 00:00:00 2001
From: Philipp Emanuel Weidmann <pew@worldwidemann.com>
Date: Sat, 13 Jun 2020 08:32:00 +0530
Subject: [PATCH] Make RuneWidth faster for code points below 0x0300

---
 runewidth.go | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/runewidth.go b/runewidth.go
index 19f8e04..dc020f5 100644
--- a/runewidth.go
+++ b/runewidth.go
@@ -101,7 +101,19 @@ func NewCondition() *Condition {
 // See http://www.unicode.org/reports/tr11/
 func (c *Condition) RuneWidth(r rune) int {
 	switch {
-	case r < 0 || r > 0x10FFFF || inTables(r, nonprint, combining, notassigned):
+	case r < 0 || r > 0x10FFFF:
+		return 0
+	// Fast path
+	case r < 0x0300: // neither combining, non-assigned or double-width
+		switch {
+		case r <= 0x001F || (0x007F <= r && r <= 0x009F) || r == 0x00AD: // non-printable
+			return 0
+		case c.EastAsianWidth && IsAmbiguousWidth(r):
+			return 2
+		default:
+			return 1
+		}
+	case inTables(r, nonprint, combining, notassigned):
 		return 0
 	case (c.EastAsianWidth && IsAmbiguousWidth(r)) || inTables(r, doublewidth):
 		return 2