perf: Improve percentDecode (#2562)

lib/fetch/dataURL.js

@@ -188,11 +188,28 @@ function stringPercentDecode (input) {
   return percentDecode(bytes)
 }
 
+/**
+ * @param {number} byte
+ */
 function isHexCharByte (byte) {
   // 0-9 A-F a-f
   return (byte >= 0x30 && byte <= 0x39) || (byte >= 0x41 && byte <= 0x46) || (byte >= 0x61 && byte <= 0x66)
 }
 
+/**
+ * @param {number} byte
+ */
+function hexByteToNumber (byte) {
+  return (
+    // 0-9
+    byte >= 0x30 && byte <= 0x39
+      ? (byte - 48)
+    // Convert to uppercase
+    // ((byte & 0xDF) - 65) + 10
+      : ((byte & 0xDF) - 55)
+  )
+}
+
 // https://url.spec.whatwg.org/#percent-decode
 /** @param {Uint8Array} input */
 function percentDecode (input) {
@@ -224,11 +241,8 @@ function percentDecode (input) {
     } else {
       // 1. Let bytePoint be the two bytes after byte in input,
       // decoded, and then interpreted as hexadecimal number.
-      const nextTwoBytes = String.fromCharCode(input[i + 1], input[i + 2])
-      const bytePoint = Number.parseInt(nextTwoBytes, 16)
-
       // 2. Append a byte whose value is bytePoint to output.
-      output[j++] = bytePoint
+      output[j++] = (hexByteToNumber(input[i + 1]) << 4) | hexByteToNumber(input[i + 2])
 
       // 3. Skip the next two bytes in input.
       i += 2