Dirty Coding Tricks

[Simon F]

And with code like that,

.. you deserve to be fired?

 

[arjan de lumens]

And with code like that, if you put a printf("%d\n",i) inside the loop and run it thru the optimizer, you'll prolly wonder why the hell am I not getting an infinite loop?

Actually, I did try, and I did get an infinite loop even with printf() in it.

Input code, in C:

#include <stdio.h>
int main(void)
        {
        int i;
        for(i=0;i<100;i--)
                {
                printf("%d\n",i);
                }
        }

Assembly code generated by gcc-4.3.3 for the main() function, compiled with optimizations (gcc command line switch -O3):

globl main
        .type   main, @function
main:
.LFB24:
        pushq   %rbx
.LCFI0:
        xorl    %ebx, %ebx
        .p2align 4,,10
        .p2align 3
.L2:
        movl    %ebx, %edx
        movl    $.LC0, %esi
        movl    $1, %edi
        xorl    %eax, %eax
        subl    $1, %ebx
        call    __printf_chk
        jmp     .L2

Excerpt of output from actually running the program:

-2147483645
-2147483646
-2147483647
-2147483648
2147483647
2147483646
2147483645
2147483644

However, if I turn optimizations off (by giving gcc the commandline switch -O0 instead of -O3), then the loop is no longer infinite.