diff --git a/datalab/bits.c b/datalab/bits.c
index f166d22..44c3fd3 100644
--- a/datalab/bits.c
+++ b/datalab/bits.c
@@ -247,10 +247,13 @@ int logicalShift(int x, int n) {
  *   Rating: 4
  */
 int swapNibblePairs(int x) {
-  int lowMask = 0x0F0F0F0F;
-  int lowPart = (x & lowMask) << 4;
-  int highPart = ((x >> 4) & lowMask);
-  return lowPart | highPart;
+  int mask = 0x0F;                 // 合法常量
+  mask = mask | (mask << 8);       // 得到 0x0F0F
+  mask = mask | (mask << 16);      // 得到 0x0F0F0F0F
+  // int lowPart = (x & mask) << 4;   // 取低 nibble 并左移
+  // int highPart = (x >> 4) & mask;  // 取高 nibble 并右移
+  // return lowPart | highPart;       // 合并
+  return ((x & mask) << 4) | ((x >> 4) & mask);
 }
 
 // P9
diff --git a/datalab/dlc b/datalab/dlc
old mode 100644
new mode 100755
index 9b34c05..8df5369
Binary files a/datalab/dlc and b/datalab/dlc differ