perf: TextEncoder.encode improvement (#3596)

cli/js/encode_utf8.ts

+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+// The following code is based off:
+// https://github.com/samthor/fast-text-encoding
+//
+// Copyright 2017 Sam Thorogood. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+//
+
+export function encodeUtf8(input: string): Uint8Array {
+  let pos = 0;
+  const len = input.length;
+
+  let at = 0; // output position
+  let tlen = Math.max(32, len + (len >> 1) + 7); // 1.5x size
+  let target = new Uint8Array((tlen >> 3) << 3); // ... but at 8 byte offset
+
+  while (pos < len) {
+    let value = input.charCodeAt(pos++);
+    if (value >= 0xd800 && value <= 0xdbff) {
+      // high surrogate
+      if (pos < len) {
+        const extra = input.charCodeAt(pos);
+        if ((extra & 0xfc00) === 0xdc00) {
+          ++pos;
+          value = ((value & 0x3ff) << 10) + (extra & 0x3ff) + 0x10000;
+        }
+      }
+      if (value >= 0xd800 && value <= 0xdbff) {
+        continue; // drop lone surrogate
+      }
+    }
+
+    // expand the buffer if we couldn't write 4 bytes
+    if (at + 4 > target.length) {
+      tlen += 8; // minimum extra
+      tlen *= 1.0 + (pos / input.length) * 2; // take 2x the remaining
+      tlen = (tlen >> 3) << 3; // 8 byte offset
+
+      const update = new Uint8Array(tlen);
+      update.set(target);
+      target = update;
+    }
+
+    if ((value & 0xffffff80) === 0) {
+      // 1-byte
+      target[at++] = value; // ASCII
+      continue;
+    } else if ((value & 0xfffff800) === 0) {
+      // 2-byte
+      target[at++] = ((value >> 6) & 0x1f) | 0xc0;
+    } else if ((value & 0xffff0000) === 0) {
+      // 3-byte
+      target[at++] = ((value >> 12) & 0x0f) | 0xe0;
+      target[at++] = ((value >> 6) & 0x3f) | 0x80;
+    } else if ((value & 0xffe00000) === 0) {
+      // 4-byte
+      target[at++] = ((value >> 18) & 0x07) | 0xf0;
+      target[at++] = ((value >> 12) & 0x3f) | 0x80;
+      target[at++] = ((value >> 6) & 0x3f) | 0x80;
+    } else {
+      // FIXME: do we care
+      continue;
+    }
+
+    target[at++] = (value & 0x3f) | 0x80;
+  }
+
+  return target.slice(0, at);
+}

cli/js/text_encoding.ts

@@ -26,6 +26,7 @@
 import * as base64 from "./base64.ts";
 import { decodeUtf8 } from "./decode_utf8.ts";
 import * as domTypes from "./dom_types.ts";
+import { encodeUtf8 } from "./encode_utf8.ts";
 import { DenoError, ErrorKind } from "./errors.ts";
 
 const CONTINUE = null;
@@ -405,6 +406,12 @@ export class TextEncoder {
   readonly encoding = "utf-8";
   /** Returns the result of running UTF-8's encoder. */
   encode(input = ""): Uint8Array {
+    // For performance reasons we utilise a highly optimised decoder instead of
+    // the general decoder.
+    if (this.encoding === "utf-8") {
+      return encodeUtf8(input);
+    }
+
     const encoder = new UTF8Encoder();
     const inputStream = new Stream(stringToCodePoints(input));
     const output: number[] = [];