From 8b2834b06aad9ed92c6d7653454b40d9d4de1d1c Mon Sep 17 00:00:00 2001 From: Jixun Wu Date: Mon, 21 Nov 2022 18:15:16 +0000 Subject: [PATCH] refactor: implement a more efficient buffer decryption algorithm for qmc cache. --- src/decrypt/qmccache.ts | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/src/decrypt/qmccache.ts b/src/decrypt/qmccache.ts index 7d66ed5..023cd73 100644 --- a/src/decrypt/qmccache.ts +++ b/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; - if (buffer[i] <= 0x3f) buffer[i] = buffer[i] * 4; - else if (buffer[i] <= 0x7f) buffer[i] = (buffer[i] - 0x40) * 4 + 1; - else if (buffer[i] <= 0xbf) buffer[i] = (buffer[i] - 0x80) * 4 + 2; - else buffer[i] = (buffer[i] - 0xc0) * 4 + 3; + let byte = buffer[i] ^ 0xf4; // xor 0xf4 + byte = ((byte & 0b0011_1111) << 2) | (byte >> 6); // rol 2 + buffer[i] = byte; } }