Bombe binaire (phase 4)% d% d

Question

J'ai une phase binaire qui ne revient pas Résultat requis i.e 12. Des suggestions?

Phase 4

Dump of assembler code for function phase_4: 
    0x000000000040100b <+0>:  sub $0x18,%rsp 
    0x000000000040100f <+4>:  lea 0x8(%rsp),%rcx 
    0x0000000000401014 <+9>:  lea 0xc(%rsp),%rdx 
    0x0000000000401019 <+14>: mov $0x40278d,%esi 
    0x000000000040101e <+19>: mov $0x0,%eax 
    0x0000000000401023 <+24>: callq 0x400b90 <__isoc99_sscanf@plt> 
    0x0000000000401028 <+29>: cmp $0x2,%eax 
=> 0x000000000040102b <+32>: je  0x401054 <phase_4+73> 
    0x000000000040102d <+34>: callq 0x401538 <explode_bomb> 
    0x0000000000401032 <+39>: mov $0xe,%edx 
    0x0000000000401037 <+44>: mov $0x0,%esi 
    0x000000000040103c <+49>: mov 0xc(%rsp),%edi 
    0x0000000000401040 <+53>: callq 0x400fd7 <func4> 
    0x0000000000401045 <+58>: cmp $0x12,%eax 
    0x0000000000401048 <+61>: je  0x40105d <phase_4+82> 
    0x000000000040104a <+63>: callq 0x401538 <explode_bomb> 
    0x000000000040104f <+68>: add $0x18,%rsp 
    0x0000000000401053 <+72>: retq 
    0x0000000000401054 <+73>: cmpl $0xe,0xc(%rsp) 
    0x0000000000401059 <+78>: jbe 0x401032 <phase_4+39> 
    0x000000000040105b <+80>: jmp 0x40102d <phase_4+34> 
    0x000000000040105d <+82>: cmpl $0x12,0x8(%rsp) 
    0x0000000000401062 <+87>: jne 0x40104a <phase_4+63> 
    0x0000000000401064 <+89>: jmp 0x40104f <phase_4+68> 
End of assembler dump. 

FUNC4 est la suivante:

Dump of assembler code for function func4: 
=> 0x0000000000400fd7 <+0>:  push %rbx   
    0x0000000000400fd8 <+1>:  mov %edx,%eax  
    0x0000000000400fda <+3>:  sub %esi,%eax  
    0x0000000000400fdc <+5>:  mov %eax,%ebx 
    0x0000000000400fde <+7>:  shr $0x1f,%ebx 
    0x0000000000400fe1 <+10>: add %eax,%ebx  
    0x0000000000400fe3 <+12>: sar %ebx 
    0x0000000000400fe5 <+14>: add %esi,%ebx  
    0x0000000000400fe7 <+16>: cmp %edi,%ebx  
    0x0000000000400fe9 <+18>: jg  0x400ff3 <func4+28> 
    0x0000000000400feb <+20>: cmp %edi,%ebx  
    0x0000000000400fed <+22>: jl  0x400fff <func4+40> 
    0x0000000000400fef <+24>: mov %ebx,%eax 
    0x0000000000400ff1 <+26>: pop %rbx 
    0x0000000000400ff2 <+27>: retq 
    0x0000000000400ff3 <+28>: lea -0x1(%rbx),%edx 
    0x0000000000400ff6 <+31>: callq 0x400fd7 <func4> 
    0x0000000000400ffb <+36>: add %eax,%ebx 
    0x0000000000400ffd <+38>: jmp 0x400fef <func4+24> 
    0x0000000000400fff <+40>: lea 0x1(%rbx),%esi 
    0x0000000000401002 <+43>: callq 0x400fd7 <func4> 
    0x0000000000401007 <+48>: add %eax,%ebx  
    0x0000000000401009 <+50>: jmp 0x400fef <func4+24> 
End of assembler dump. 

J'ai écrit un programme test C que je crois équivalent au code de montage ci-dessus pour FUNC4.

#include <stdio.h> 

int main() 
{ 

    int i=0; 
    for(int i=0;i<15;i++) 
    { 
    int z=func4(i,0,14); 
    printf("in main program: For input %d -> %d\n",i,z); 
    } 
    return 0; 
} 

int func4(int x, int low, int high) { 
    int mid = (low + high)/2; 

    if (x == mid) { 
     return (mid); 
    } else if (x < mid) { 
     int w=mid+func4(x, low, mid - 1); 
     return w; 
    } else { 
     int p=mid+func4(x, mid + 1, high); 
     return p; 
    } 
} 

Ce programme retourne sortie comme suit:

in main program: For input 0 -> 11                        
in main program: For input 1 -> 11                        
in main program: For input 2 -> 13                        
in main program: For input 3 -> 10                        
in main program: For input 4 -> 19                        
in main program: For input 5 -> 15                        
in main program: For input 6 -> 21                        
in main program: For input 7 -> 7                        
in main program: For input 8 -> 35                        
in main program: For input 9 -> 27                        
in main program: For input 10 -> 37 
in main program: For input 11 -> 18                       
in main program: For input 12 -> 43                       
in main program: For input 13 -> 31                       
in main program: For input 14 -> 45 

je me suis dit que la fonction prendra deux arguments et le second argument doit être 12. Mais je ne suis pas d'obtenir la valeur 12 est revenu de FUNC4.

Des suggestions?

Answer 1

Le code de montage est en fait attend une valeur de 0x12 (18 au lieu de 12) func4:

0x0000000000401040 <+53>: callq 0x400fd7 <func4> 
0x0000000000401045 <+58>: cmp $0x12,%eax    <- Compare result to 0x12 
0x0000000000401048 <+61>: je  0x40105d <phase_4+82> 
0x000000000040104a <+63>: callq 0x401538 <explode_bomb> 

Je ne l'ai pas regardé votre traduction C de func4 pour l'exactitude, mais en supposant qu'il est correct, il semble comme func4(11, 0, 14) vous donne ce que vous voulez.