init

Author: lesheng

.gitignore

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+# Prerequisites
+*.d
+
+# Object files
+*.o
+*.ko
+*.obj
+*.elf
+
+# Linker output
+*.ilk
+*.map
+*.exp
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Libraries
+*.lib
+*.a
+*.la
+*.lo
+
+# Shared objects (inc. Windows DLLs)
+*.dll
+*.so
+*.so.*
+*.dylib
+
+# Executables
+*.exe
+*.out
+*.app
+*.i*86
+*.x86_64
+*.hex
+
+# Debug files
+*.dSYM/
+*.su
+*.idb
+*.pdb
+
+# Kernel Module Compile Results
+*.mod*
+*.cmd
+.tmp_versions/
+modules.order
+Module.symvers
+Mkfile.old
+dkms.conf

.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "gcc.exe - Build and debug active file",
+            "type": "cppdbg",
+            "request": "launch",
+            "program": "${fileDirname}\\${fileBasenameNoExtension}.exe",
+            "args": [],
+            "stopAtEntry": false,
+            "cwd": "${workspaceFolder}",
+            "environment": [],
+            "externalConsole": false,
+            "MIMode": "gdb",
+            "miDebuggerPath": "C:\\Program Files\\mingw-w64\\x86_64-8.1.0-posix-seh-rt_v6-rev0\\mingw64\\bin\\gdb.exe",
+            "setupCommands": [
+                {
+                    "description": "Enable pretty-printing for gdb",
+                    "text": "-enable-pretty-printing",
+                    "ignoreFailures": true
+                }
+            ],
+            "preLaunchTask": "C/C++: gcc.exe build active file"
+        }
+    ]
+}

.vscode/tasks.json

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+{
+    "tasks": [
+        {
+            "type": "cppbuild",
+            "label": "C/C++: gcc.exe build active file",
+            "command": "C:\\Program Files\\mingw-w64\\x86_64-8.1.0-posix-seh-rt_v6-rev0\\mingw64\\bin\\gcc.exe",
+            "args": [
+                "-g",
+                "${file}",
+                "-o",
+                "${fileDirname}\\${fileBasenameNoExtension}.exe"
+            ],
+            "options": {
+                "cwd": "${workspaceFolder}"
+            },
+            "problemMatcher": [
+                "$gcc"
+            ],
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "detail": "Task generated by Debugger."
+        }
+    ],
+    "version": "2.0.0"
+}

chap1/data_cast.c

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+#include <stdio.h>
+
+typedef unsigned char *byte_pointer;
+
+void show_bytes(byte_pointer start,size_t len){
+    size_t i;
+    for(i=0;i<len;i++){
+        printf("%.2x",start[i]);
+    }
+    printf("\n");
+}
+
+void show_int(int x){
+    show_bytes((byte_pointer)&x,sizeof(int));
+}
+
+void show_float(float x){
+    show_bytes((byte_pointer)&x,sizeof(float));
+}
+
+void show_pointer(void *x){
+    show_bytes((byte_pointer)&x,sizeof(void*));
+}
+
+void main(int val){
+    int ival=val;
+    float fval=(float)ival;
+    int *pval=&ival;
+    show_int(ival);
+    show_float(fval);
+    show_pointer(pval);
+}

chap1/ex2_10.c

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+#include <stdio.h>
+
+void inplace_swap(int *x,int *y){
+    *y=*x^*y;
+    *x=*x^*y;
+    *y=*x^*y;
+}
+
+void reverse_array(int a[],int cnt){
+    int first,last;
+    for(first=0,last=cnt-1;
+    first<=last;
+    first++,last--){
+        inplace_swap(&a[first],&a[last]);
+    }
+}
+
+void main(){
+
+    int b[5]={1,2,3,4,5};
+     reverse_array(&b,5);
+    for(int i=0;i<5;i++){
+        printf("%d ",b[i]);
+    }
+    // 最后一次交换 swap(b[2],b[2]) 
+    // a^a=0 加法逆元
+    printf("\n");
+
+    int a[4]={1,2,3,4};
+    reverse_array(&a,4);
+    for(int i=0;i<4;i++){
+        printf("%d ",a[i]);
+        // printf("%.2x",a[i]);
+    }
+    printf("\n");
+}

chap1/ex2_13.c

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+#include <stdio.h>
+
+void main(){
+    int d= 0b11111101;
+    int mask =0b0000;
+    int result= bis(d,mask);
+    printf("%d",result);
+}
+
+
+//位设置:以m为掩码,若m位置上为1,则将z相应位设置为1
+int bis(int x,int m) {
+    int z = x | m;
+    return z;
+}
+//位清除:以m为掩码,若m位置上为1,则将z相应位设置为0
+int bic(int x,int m) {
+    int z = x & (x ^ m);
+    return z;
+}

t/mi.c

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+#include <stdio.h>
+
+// 幂:循环
+unsigned mi_loop(unsigned a,unsigned m)
+{
+    unsigned result;
+    for (int i=0;i<m;i++){
+        result*=a;
+    }
+    return result;
+}
+
+// 幂：迭代，每次迭代减一
+unsigned mi_iterative(unsigned a,unsigned m){
+    // 非0为true，!m等价m==0
+    if(!m){
+        return 1;
+    }
+    unsigned b=mi_iterative(a , m - 1);
+    return a * b;
+    // return a*mi_iterative(a , m - 1);
+}
+
+// 幂：快速迭代,每次迭代右移一位
+unsigned mi_fast_iterative(unsigned a , unsigned m)
+{
+    // if(m=0)
+    if (!m){
+        return 1;
+    }
+    // if (m%2=0) 
+    // m&1>0 -> m的最低位是1 -> m是奇数
+    if (m & 1){
+        // a^m=a*(a^2)^(m/2)
+        return a * mi_fast_iterative(a * a , m >> 1);
+    }
+    // a^m=(a^2)^(m/2)
+    return mi_fast_iterative(a * a , m >> 1);
+}
+
+void main(){
+   printf("%d",mi_iterative(2,4));
+   printf("%d",mi_fast_iterative(2,5));
+}