perf: Optimize TextEncoder and TextDecoder (#4430)

* add tests for "Deno.core.encode" and "Deno.core.decode" for empty inputs
* use "Deno.core.encode" in "TextEncoder"
* use "Deno.core.decode" in "TextDecoder"
* remove "core_decode" and "core_encode" benchmarks

7 files changed, 32 insertions, 156 deletions

diff --git a/cli/js/web/encode_utf8.ts b/cli/js/web/encode_utf8.ts
deleted file mode 100644
index 04e2560b7..000000000
--- a/cli/js/web/encode_utf8.ts
+++ /dev/null
@@ -1,80 +0,0 @@
-// 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);
-}
diff --git a/cli/js/web/text_encoding.ts b/cli/js/web/text_encoding.ts
index 2da53d934..5f04972aa 100644
--- a/cli/js/web/text_encoding.ts
+++ b/cli/js/web/text_encoding.ts
@@ -26,7 +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 { core } from "../core.ts";
 
 const CONTINUE = null;
 const END_OF_STREAM = -1;
@@ -352,6 +352,15 @@ export class TextDecoder {
       bytes = new Uint8Array(0);
     }
 
+    // For simple utf-8 decoding "Deno.core.decode" can be used for performance
+    if (
+      this._encoding === "utf-8" &&
+      this.fatal === false &&
+      this.ignoreBOM === false
+    ) {
+      return core.decode(bytes);
+    }
+
     // For performance reasons we utilise a highly optimised decoder instead of
     // the general decoder.
     if (this._encoding === "utf-8") {
@@ -396,10 +405,9 @@ interface TextEncoderEncodeIntoResult {
 export class TextEncoder {
   readonly encoding = "utf-8";
   encode(input = ""): Uint8Array {
-    // For performance reasons we utilise a highly optimised decoder instead of
-    // the general decoder.
+    // Deno.core.encode() provides very efficient utf-8 encoding
     if (this.encoding === "utf-8") {
-      return encodeUtf8(input);
+      return core.encode(input);
     }
 
     const encoder = new UTF8Encoder();
diff --git a/cli/tests/core_decode_perf.js b/cli/tests/core_decode_perf.js
deleted file mode 100644
index fc00b8996..000000000
--- a/cli/tests/core_decode_perf.js
+++ /dev/null
@@ -1,37 +0,0 @@
-const mixed = new TextEncoder().encode("@Ā๐😀");
-
-function generateRandom(bytes) {
-  const result = new Uint8Array(bytes);
-  let i = 0;
-  while (i < bytes) {
-    const toAdd = Math.floor(Math.random() * Math.min(4, bytes - i));
-    switch (toAdd) {
-      case 0:
-        result[i] = mixed[0];
-        i++;
-        break;
-      case 1:
-        result[i] = mixed[1];
-        result[i + 1] = mixed[2];
-        i += 2;
-        break;
-      case 2:
-        result[i] = mixed[3];
-        result[i + 1] = mixed[4];
-        result[i + 2] = mixed[5];
-        i += 3;
-        break;
-      case 3:
-        result[i] = mixed[6];
-        result[i + 1] = mixed[7];
-        result[i + 2] = mixed[8];
-        result[i + 3] = mixed[9];
-        i += 4;
-        break;
-    }
-  }
-  return result;
-}
-
-const randomData = generateRandom(1024);
-for (let i = 0; i < 10_000; i++) Deno.core.decode(randomData);
diff --git a/cli/tests/core_encode_perf.js b/cli/tests/core_encode_perf.js
deleted file mode 100644
index 5cde81c7a..000000000
--- a/cli/tests/core_encode_perf.js
+++ /dev/null
@@ -1,32 +0,0 @@
-const mixed = "@Ā๐😀";
-
-function generateRandom(bytes) {
-  let result = "";
-  let i = 0;
-  while (i < bytes) {
-    const toAdd = Math.floor(Math.random() * Math.min(4, bytes - i));
-    switch (toAdd) {
-      case 0:
-        result += mixed[0];
-        i++;
-        break;
-      case 1:
-        result += mixed[1];
-        i++;
-        break;
-      case 2:
-        result += mixed[2];
-        i++;
-        break;
-      case 3:
-        result += mixed[3];
-        result += mixed[4];
-        i += 2;
-        break;
-    }
-  }
-  return result;
-}
-
-const randomData = generateRandom(1024);
-for (let i = 0; i < 10_000; i++) Deno.core.encode(randomData);
diff --git a/core/bindings.rs b/core/bindings.rs
index 3745abf69..88bdf7f30 100644
--- a/core/bindings.rs
+++ b/core/bindings.rs
@@ -632,7 +632,20 @@ fn encode(
   };
   let text_str = text.to_rust_string_lossy(scope);
   let text_bytes = text_str.as_bytes().to_vec().into_boxed_slice();
-  let buf = boxed_slice_to_uint8array(scope, text_bytes);
+
+  let buf = if text_bytes.is_empty() {
+    let ab = v8::ArrayBuffer::new(scope, 0);
+    v8::Uint8Array::new(ab, 0, 0).expect("Failed to create UintArray8")
+  } else {
+    let buf_len = text_bytes.len();
+    let backing_store =
+      v8::ArrayBuffer::new_backing_store_from_boxed_slice(text_bytes);
+    let mut backing_store_shared = backing_store.make_shared();
+    let ab =
+      v8::ArrayBuffer::with_backing_store(scope, &mut backing_store_shared);
+    v8::Uint8Array::new(ab, 0, buf_len).expect("Failed to create UintArray8")
+  };
+
   rv.set(buf.into())
 }
 
diff --git a/core/encode_decode_test.js b/core/encode_decode_test.js
index 8a366dd66..294144593 100644
--- a/core/encode_decode_test.js
+++ b/core/encode_decode_test.js
@@ -27,12 +27,18 @@ function main() {
     108, 100 
   ];
 
+  const empty = Deno.core.encode("");
+  if (empty.length !== 0) throw new Error("assert");
+
   assertArrayEquals(Array.from(Deno.core.encode("𝓽𝓮𝔁𝓽")), fixture1);
   assertArrayEquals(
     Array.from(Deno.core.encode("Hello \udc12\ud834 World")),
     fixture2
   );
 
+  const emptyBuf = Deno.core.decode(new Uint8Array(0));
+  if (emptyBuf !== "") throw new Error("assert");
+
   assert(Deno.core.decode(new Uint8Array(fixture1)) === "𝓽𝓮𝔁𝓽");
   assert(Deno.core.decode(new Uint8Array(fixture2)) === "Hello �� World");
 }
diff --git a/tools/benchmark.py b/tools/benchmark.py
index 3891bc207..c29ca3e8c 100755
--- a/tools/benchmark.py
+++ b/tools/benchmark.py
@@ -28,9 +28,7 @@ exec_time_benchmarks = [
     ("workers_startup", ["cli/tests/workers_startup_bench.ts"]),
     ("workers_round_robin", ["cli/tests/workers_round_robin_bench.ts"]),
     ("text_decoder", ["cli/tests/text_decoder_perf.js"]),
-    ("core_decode", ["cli/tests/core_decode_perf.js"]),
     ("text_encoder", ["cli/tests/text_encoder_perf.js"]),
-    ("core_encode", ["cli/tests/core_encode_perf.js"]),
 ]