free21.md

free21

Polyglot code to print "FREE " 21 times in both (obfuscated) C and brainf*ck. The C version prints an additional newline character at the end.

/****************************************************************************/

          /****[****/
        #define x  0x0a
      #define o   putchar
     #define          q *p
     #define          w <<1
     char a
     [x]={0}
     ;char q
     =a;void
     main(){q+=x;++
     p;++q;++p;++p;
     ++q;++          q;  ++p;++       q;++q;          p-=04;
     while           (q){++p;q+=    (*(p+-1)w)       %0x6;++p;
     q+=(*           (p-2    )w)%  (x w)   ;q-=    (*(p-   2)w)%
     0x6;++          p;q           +=((*   (p+-3  )w)%x)   w;++p;
     q+=(((          *(p           -4)w)%x)+((*   (p-4)w)%0x6))>>
     1;p-=(          x-2           )>>1;          --q;
     }++p;          while          (q){     ++p;  o(q)       ;++p
     ;o(q)           ;--            p;--q;o(q);    o(q);++q;++p;    ++p
     ;o(q)          ;p-=              0xf>>q%        x;--q;}o(x     );}

/*]++++++++++>+>>++>++<<<<[>++>+++++++>++++++++>+++<<<<-]>[>.>.<-..+>>.<<<-]*/

Explanation

Both codes follow the same general procedure.

An array of memory cells holds integer values to control the program flow or be interpreted as ASCII characters. Five cells are used:

Cell	Purpose
0	Loop counter
1	Loop counter
2	Character
3	Character
4	Character

The first loop counter controls a loop to increment values in the other cells. The second loop counter controls the number of times "FREE " is printed.

All cells initially hold a value of 0.

At the beginning of execution, the first loop counter is set to 10, the second loop counter is set to 1, and the character cells 3 and 4 are set to 2. (Cell 2 is not modified and remains set to 0.)

++++++++++
>+
>>++
>++

The instruction pointer is moved back to cell 0 (the first loop counter) and the first loop is started. The first loop iterates 10 times. During each iteration it adds 2 to cell 1, 7 to cell 2, 8 to cell 3, and 3 to cell 4, then subtracts 1 from cell 0. (The C version follows a different procedure with the same results at the end of the loop.)

<<<<[
    >++
    >+++++++
    >++++++++
    >+++
    <<<<-
]

At the end of the first loop, the cell values are as follows:

Cell	Value
0	0
1	21
2	70 (ASCII "F")
3	82 (ASCII "R")
4	32 (ASCII " ")

Next, the instruction pointer is moved to cell 1 and the second loop is started. The second loop iterates 21 times. During each iteration, it prints cell 2, then cell 3, subtracts 1 from cell 2, prints cell 2 twice, adds 1 to cell 2, prints cell 4, and subtracts 1 from cell 1.

>[
    >.
    >.
    <-..+
    >>.
    <<<-
]