add TextDecoder for string to UTF32

src/core/input/TextDecoder.ts

@@ -0,0 +1,87 @@
+/**
+ * Copyright (c) 2019 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+/**
+ * StringToUtf32 - decodes UTF16 sequences into UTF32 codepoints.
+ * To keep the decoder in line with JS strings it handles single surrogates as UCS2.
+ */
+export class StringToUtf32 {
+  private _interim: number = 0;
+
+  /**
+   * Clears interim and resets decoder to clean state.
+   */
+  public clear(): void {
+    this._interim = 0;
+  }
+
+  /**
+   * Decode JS string to UTF32 codepoints.
+   * The methods assumes stream input and will store partly transmitted
+   * surrogate pairs and decode them with the next data chunk.
+   * Note: The method does no bound checks for target, therefore make sure
+   * the provided input data does not exceed the size of `target`.
+   * Returns the number of written codepoints in `target`.
+   */
+  decode(input: string, target: Uint32Array): number {
+    const length = input.length;
+
+    if (!length) {
+      return 0;
+    }
+
+    let size = 0;
+    let startPos = 0;
+
+    // handle leftover surrogate high
+    if (this._interim) {
+      const second = input.charCodeAt(startPos++);
+      if (0xDC00 <= second && second <= 0xDFFF) {
+        target[size++] = (this._interim - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
+      } else {
+        // illegal codepoint (USC2 handling)
+        target[size++] = this._interim;
+        target[size++] = second;
+      }
+      this._interim = 0;
+    }
+
+    for (let i = startPos; i < length; ++i) {
+      const code = input.charCodeAt(i);
+      // surrogate pair first
+      if (0xD800 <= code && code <= 0xDBFF) {
+        if (++i >= length) {
+          this._interim = code;
+          return size;
+        }
+        const second = input.charCodeAt(i);
+        if (0xDC00 <= second && second <= 0xDFFF) {
+          target[size++] = (code - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
+        } else {
+          // illegal codepoint (USC2 handling)
+          target[size++] = code;
+          target[size++] = second;
+        }
+        continue;
+      }
+      target[size++] = code;
+    }
+    return size;
+  }
+}
+
+/**
+ * Polyfill - Convert UTF32 codepoint into JS string.
+ */
+export function stringFromCodePoint(codePoint: number): string {
+  if ((String as any).fromCodePoint) {
+    return (String as any).fromCodePoint(codePoint);
+  }
+  if (codePoint > 0xFFFF) {
+    codePoint -= 0x10000;
+    return String.fromCharCode((codePoint >> 10) + 0xD800) + String.fromCharCode((codePoint % 0x400) + 0xDC00);
+  }
+  return String.fromCharCode(codePoint);
+}