From fa89e1776b107fd602213af42c5f8dc6e722b668 Mon Sep 17 00:00:00 2001
From: Per Bothner <per@bothner.com>
Date: Sun, 21 May 2023 10:29:13 -0700
Subject: [PATCH] Optimize UnicodeGraphemeProvider for the ASCII case.

---
 .../src/UnicodeGraphemeProvider.ts                       | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/addons/xterm-addon-unicode-graphemes/src/UnicodeGraphemeProvider.ts b/addons/xterm-addon-unicode-graphemes/src/UnicodeGraphemeProvider.ts
index 87ec8d32..00740dac 100644
--- a/addons/xterm-addon-unicode-graphemes/src/UnicodeGraphemeProvider.ts
+++ b/addons/xterm-addon-unicode-graphemes/src/UnicodeGraphemeProvider.ts
@@ -15,6 +15,15 @@ export class UnicodeGraphemeProvider implements IUnicodeVersionProvider {
   }
 
   public charProperties(codepoint: number, preceding: UnicodeCharProperties): UnicodeCharProperties {
+    // Optimize the simple ASCII case, under the condition that
+    // UnicodeService.extractCharKind(preceding) === GRAPHEME_BREAK_Other
+    // (which also covers the case that preceding === 0).
+
+    if ((codepoint >= 32 && codepoint < 127) && (preceding >> 3) === 0) {
+      // Inlined UnicodeService.createPropertyValue(GRAPHEME_BREAK_Other, 1, false)
+      return 1;
+    }
+
     let charInfo = UC.getInfo(codepoint);
     let w = UC.infoToWidthInfo(charInfo);
     let shouldJoin = false;