speedup utf32ToString conversion

src/EscapeSequenceParser.ts

@@ -567,7 +567,7 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
             if (j >= length
                 || (code = data[j]) < 0x20
                 || (code > 0x7f && code <= 0x9f)) {
-              osc += utf32ToString(data.subarray(i, j));
+              osc += utf32ToString(data, i, j);
               i = j - 1;
               break;
             }

src/common/TypedArrayUtils.ts

@@ -1,5 +1,3 @@
-import { stringFromCodePoint } from '../core/input/TextDecoder';
-
 /**
  * Copyright (c) 2018 The xterm.js authors. All rights reserved.
  * @license MIT
@@ -54,17 +52,17 @@ export function concat<T extends TypedArray>(a: T, b: T): T {
 
 /**
  * Convert UTF32 char codes into JS string.
- * Note the typed array is not limited to Uint16Array, make sure to align
- * the values to 0-65535 integer for other typed array types, otherwise
- * the conversion will fail.
  */
-export function utf32ToString<T extends TypedArray>(data: T): string {
-  if ((String as any).fromCodePoint) {
-    return (String as any).fromCodePoint.apply(null, data);
-  }
+export function utf32ToString<T extends TypedArray>(data: T, start: number = 0, end: number = data.length): string {
   let result = '';
-  for (let i = 0; i < data.length; ++i) {
-    result += stringFromCodePoint(data[i]);
+  let cp;
+  for (let i = start; i < end; ++i) {
+    if ((cp = data[i]) > 0xFFFF) {
+      cp -= 0x10000;
+      result += String.fromCharCode((cp >> 10) + 0xD800) + String.fromCharCode((cp % 0x400) + 0xDC00);
+    } else {
+      result += String.fromCharCode(cp);
+    }
   }
   return result;
 }