C与汇编

Signed vs unsigned

 1     char c = -1;
 2 00A81962  mov         byte ptr [c],0FFh  
 3     unsigned char uc = -1;
 4 00A81966  mov         byte ptr [uc],0FFh  
 5 
 6     if (uc == c)
 7 00A8196A  movzx       eax,byte ptr [uc]  
 8 00A8196E  movsx       ecx,byte ptr [c]  
 9 00A81972  cmp         eax,ecx  
10 00A81974  jne         main+53h (0A81983h)  
11         printf("1\n");
12 00A81976  push        offset string "1\n" (0A87B7Ch)  
13 00A8197B  call        _printf (0A8104Bh)  
14 00A81980  add         esp,4  
15
16     if ((char)uc == c) 
17 00A81983  movsx       eax,byte ptr [uc]  
18 00A81987  movsx       ecx,byte ptr [c]  
19 00A8198B  cmp         eax,ecx  
20 00A8198D  jne         main+6Ch (0A8199Ch)  
21         printf("1\n");
22 00A8198F  push        offset string "1\n" (0A87B7Ch)  
23 00A81994  call        _printf (0A8104Bh)  
24 00A81999  add         esp,4

Multi-level Pointer

 1     printf("Value of var using level-4"
 2 00E2198B  mov         eax,dword ptr [ptr4]  
 3 00E2198E  mov         ecx,dword ptr [eax]  
 4 00E21990  mov         edx,dword ptr [ecx]  
 5 00E21992  mov         eax,dword ptr [edx]  
 6 00E21994  cvtss2sd    xmm0,dword ptr [eax]  
 7 00E21998  sub         esp,8  
 8 00E2199B  movsd       mmword ptr [esp],xmm0  
 9 00E219A0  push        offset string "Value of var using level-4 poin@"... (0E27BE4h)  
10 00E219A5  call        _printf (0E2104Bh)  
11 00E219AA  add         esp,0Ch  
12         " pointer = %f\n", ****ptr4);

 

posted @ 2022-04-14 17:07  anyboo  阅读(38)  评论(0)  编辑  收藏  举报