Optimize WebCrypto bytes to hex conversion.

- Improvement depends on number of digests performed.
- Browser:
  - Precompute a byte-to-hex table.
  - ~4-9% improvement overall using improved algorithm in Node.js.
  - Browsers should see similar speedup. Node.js normally will use the
    method below.
- Node.js:
  - Use native `Buffer.from(...).toString('hex')` conversion.
  - ~5-12% improvement overall.
  - The non-WebCrypto MessageDigest on Node.js is still faster.

Author: davidlehn

CHANGELOG.md

@@ -17,6 +17,10 @@
 - Refactor `MessageDigest-browser.js` to `MessageDigest-webcrypto.js` so it can
   also be optionally used with Node.js.
 - Move platform specific support into `platform.js` and `platform-browser.js`.
+- Optimize WebCrypto bytes to hex conversion:
+  - Improvement depends on number of digests performed.
+  - Node.js using the improved browser algorithm can be ~4-9% faster overall.
+  - Node.js native `Buffer` conversion can be ~5-12% faster overall.
 
 ### Fixed
 - Disable native lib tests in a browser.

lib/MessageDigest-webcrypto.js

@@ -3,7 +3,7 @@
  */
 'use strict';
 
-const {crypto} = require('./platform');
+const {bufferToHex, crypto} = require('./platform');
 
 module.exports = class MessageDigest {
   /**
@@ -31,13 +31,7 @@ module.exports = class MessageDigest {
 
   async digest() {
     const data = new TextEncoder().encode(this._content);
-    const buffer = new Uint8Array(
-      await crypto.subtle.digest(this.algorithm, data));
-    // return digest in hex
-    let hex = '';
-    for(let i = 0; i < buffer.length; ++i) {
-      hex += buffer[i].toString(16).padStart(2, '0');
-    }
-    return hex;
+    const buffer = await crypto.subtle.digest(this.algorithm, data);
+    return bufferToHex(buffer);
   }
 };

lib/platform-browser.js

@@ -9,3 +9,18 @@ exports.setImmediate = setImmediate;
 
 // WebCrypto
 exports.crypto = globalThis.crypto;
+
+// precompute byte to hex table
+const byteToHex = [];
+for(let n = 0; n <= 0xff; ++n) {
+  byteToHex.push(n.toString(16).padStart(2, '0'));
+}
+
+exports.bufferToHex = function bufferToHex(buffer) {
+  let hex = '';
+  const bytes = new Uint8Array(buffer);
+  for(let i = 0; i < bytes.length; ++i) {
+    hex += byteToHex[bytes[i]];
+  }
+  return hex;
+};

lib/platform.js

@@ -8,3 +8,7 @@ exports.setImmediate = setImmediate;
 // WebCrypto
 const crypto = require('node:crypto');
 exports.crypto = crypto.webcrypto;
+
+exports.bufferToHex = function bufferToHex(buffer) {
+  return Buffer.from(buffer).toString('hex');
+};