refactor: implement a more efficient buffer decryption algorithm for qmc cache.

src/decrypt/qmccache.ts

@@ -16,11 +16,9 @@ import { parseBlob as metaParseBlob } from 'music-metadata-browser';
 export function DecryptBuffer(buffer: Uint8Array | Buffer) {
   let length = buffer.byteLength;
   for (let i = 0; i < length; i++) {
-    buffer[i] ^= 0xf4;
+    let byte = buffer[i] ^ 0xf4; // xor 0xf4
-    if (buffer[i] <= 0x3f) buffer[i] = buffer[i] * 4;
+    byte = ((byte & 0b0011_1111) << 2) | (byte >> 6); // rol 2
-    else if (buffer[i] <= 0x7f) buffer[i] = (buffer[i] - 0x40) * 4 + 1;
+    buffer[i] = byte;
-    else if (buffer[i] <= 0xbf) buffer[i] = (buffer[i] - 0x80) * 4 + 2;
-    else buffer[i] = (buffer[i] - 0xc0) * 4 + 3;
   }
 }