diff --git a/README.md b/README.md
new file mode 100644
index 0000000..a6844fc
--- /dev/null
+++ b/README.md
@@ -0,0 +1,8 @@
+# CS:APP Labs    
+
+最近在啃CSAPP，同时做了些配套的labs，这个项目给了一些labs的解答，都是我参考了Google一点点啃出来的T_T，还有一些是我写的笔记。     
+### 目录：
+- labs: 包含从[Lab Assignments](http://csapp.cs.cmu.edu/3e/labs.html)下载来的实验文件，其中 bits.c 为题目列表和我写的解答；    
+- notes: 包含我写的笔记；
+
+
diff --git a/labs/datalab-handout.tar b/labs/datalab-handout.tar
deleted file mode 100755
index 9e94552..0000000
Binary files a/labs/datalab-handout.tar and /dev/null differ
diff --git a/labs/datalab-handout/bits.c b/labs/datalab-handout/bits.c
index 62fd6ac..2196dfe 100755
--- a/labs/datalab-handout/bits.c
+++ b/labs/datalab-handout/bits.c
@@ -161,11 +161,12 @@ int getByte(int x, int n) {
  *   Rating: 3 
  */
 int logicalShift(int x, int n) {
+  int mask=((0x1<<(32+~n))+~0)|(0x1<<(32+~n));
+  return (x>>n)&mask;
 /*  int c=((0x1<<31>>31)^0x1)<<31;
   return ((x>>n)^(c>>n)); it's wrong for 0x0>>0x1==0x0
 */
-/*Bug: return ~((~x)>>n); it's wrong for ~x contains all 32 bits,
-  as ~(0x10000000)==(0x0000000001111111) in x86-64?
+/*Bug: return ~((~x)>>n); it's wrong for ~x is postive while x is negative
 */ 
 }
 /*
@@ -212,7 +213,9 @@ int tmin(void) {
  *   Rating: 2
  */
 int fitsBits(int x, int n) {
-  return 2;
+  int c=33+~n;
+  int t=(x<<c)>>c;
+  return !(x^t);
 }
 /* 
  * divpwr2 - Compute x/(2^n), for 0 <= n <= 30
@@ -264,7 +267,7 @@ int isLessOrEqual(int x, int y) {
  *   Rating: 4
  */
 int ilog2(int x) {
-  return 2;
+  return !!(x)+!!(x>>1)+;
 }
 /* 
  * float_neg - Return bit-level equivalent of expression -f for
diff --git a/labs/datalab-handout/btest b/labs/datalab-handout/btest
index 40e0581..023cd77 100755
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diff --git a/notes/README.md b/notes/README.md
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index 0000000..e69de29