From 9302ebd75164835b985fd511746689c32cb2d55c Mon Sep 17 00:00:00 2001
From: Andrew <realendermanch@gmail.com>
Date: Sun, 4 Jun 2023 15:06:51 +0300
Subject: [PATCH] Abstract FIRSTNBITS(), fix logic

---
 src/header.h |  2 ++
 src/xp.cpp   | 14 +++++++-------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/header.h b/src/header.h
index 84c308e..6017459 100644
--- a/src/header.h
+++ b/src/header.h
@@ -39,6 +39,8 @@
 #define FIELD_BITS_2003     512
 #define FIELD_BYTES_2003    64
 
+#define FIRSTNBITS(field, n)           ((field) & ((1ULL << (n)) - 1))
+
 // Confirmation ID generator constants
 #define SUCCESS 0
 #define ERR_TOO_SHORT 1
diff --git a/src/xp.cpp b/src/xp.cpp
index cabda5a..933ba53 100644
--- a/src/xp.cpp
+++ b/src/xp.cpp
@@ -24,21 +24,21 @@ void unpackXP(DWORD (&pRaw)[4], DWORD &pSerial, DWORD &pHash, DWORD (&pSignature
     // log2(24^25) = 114.
 
     // Serial = Bits [0..30] -> 31 bits
-    pSerial = pRaw[0] & 0x7fffffff;
+    pSerial = FIRSTNBITS(pRaw[0], 31);
 
     // Hash (e) = Bits [31..58] -> 28 bits
-    pHash = ((pRaw[0] >> 31) | (pRaw[1] << 1)) & 0xfffffff;
+    pHash = FIRSTNBITS(pRaw[1] << 1 | pRaw[0] >> 31, 28);
 
     // Signature (s) = Bits [59..113] -> 55 bits
-    pSignature[0] = (pRaw[1] >> 27) | (pRaw[2] << 5);
-    pSignature[1] = (pRaw[2] >> 27) | (pRaw[3] << 5);
+    pSignature[0] = pRaw[2] << 5 | pRaw[1] >> 27;
+    pSignature[1] = pRaw[3] << 5 | pRaw[2] >> 27;
 }
 
 /* Packs the Windows XP Product Key. */
 void packXP(DWORD (&pRaw)[4], DWORD pSerial, DWORD pHash, DWORD (&pSignature)[2]) {
-    pRaw[0] = pSerial | ((pHash & 1) << 31);
-    pRaw[1] = (pHash >> 1) | ((pSignature[0] & 0x1f) << 27);
-    pRaw[2] = (pSignature[0] >> 5) | (pSignature[1] << 27);
+    pRaw[0] = pSerial | FIRSTNBITS(pHash, 1) << 31;
+    pRaw[1] = FIRSTNBITS(pSignature[0], 5) << 27 | pHash >> 1;
+    pRaw[2] = pSignature[1] << 27 | pSignature[0] >> 5;
     pRaw[3] = pSignature[1] >> 5;
 }