bf.c

/* The world's smallest Brainfuck interpreter in C, by Kang Seonghoon
 * http://j.mearie.org/post/1181041789/brainfuck-interpreter-in-2-lines-of-c */
s[99],*r=s,*d,c;main(a,b){char*v=1[d=b];for(;c=*v++%93;)for(b=c&2,b=c%7?a&&(c&17
?c&1?(*r+=b-1):(r+=b-1):syscall(4-!b,b,r,1),0):v;b&&c|a**r;v=d)main(!c,&a);d=v;}

A lot of pointer arithmatic and untyped variables. Maybe gcc -m32 means 32-bit ints? I guess I have to phone ask the GPT to answer this one.

This is an example of obfuscated C code — it’s intentionally written in a cryptic, unreadable way using obscure pointer arithmetic, operator overloading, and terse expressions. Let's break it down to figure out what it’s doing.

---

Step-by-step Breakdown

Declaration:

s[99], *r = s, *d, c;

• s[99] declares an array of 99 integers.
• *r = s sets r as a pointer to s (i.e., beginning of array).
• *d, c declares d as a pointer, c as an int.

So s is the data buffer, r is the current pointer into it, d will be a pointer, c is a char/int used in the main loop.

---

Main function signature

main(a, b)

Old-style K&R function declaration. a and b are parameters.

• a is treated like an int
• b is treated like char ** in some places

---

Initial pointer setup

char *v = 1[d = b];

This means:

• d = b assigns b to d
• 1[d] is the same as d[1] (pointer syntax)
• So v = d[1]

Assuming b is char **argv, then v = argv[1]

So v now points to the first command-line argument string

---

Outer for loop

for (; c = *v++ % 93;)

• This reads each character from v (i.e. the command-line argument)
• Takes ASCII value mod 93
• Stores result in c
• Continues loop while c is non-zero

---

Inner for loop

for (b = c & 2, b = c % 7 ? a && (c & 17 ?
    c & 1 ? ( * r += b - 1) : (r += b - 1) : syscall(4 - !b, b, r, 1), 0) : v;
     b && c | a ** r;
     v = d)
    main(!c, &a);

This is where things get dense. Here's a breakdown:

• b = c & 2 extracts bit 1 of c

• b = c % 7 ? ... : v:

  • If c % 7 is true:
    • If a and (c & 17):
      • If c & 1: *r += b - 1
      • Else: r += b - 1
    • Else: syscall(4 - !b, b, r, 1)
  • Then comma operator evaluates to 0 (meaning no change to b)

• The loop condition:

  • b && (c | a ** r) — continues looping if b is nonzero and expression doesn't short-circuit

• In loop body:

  main(!c, &a);

  Recursively calls main

• After loop: d = v;

---

Summary of What It Does

This is a small ASCII-art or brainf*ck-style interpreter, often used in programming contests or obfuscation competitions like the IOCCC.

It:

• Reads characters from command-line input
• Interprets them as a kind of bytecode
• Manipulates a data tape (s[] via pointer r)
• Uses recursion, pointer arithmetic, and the syscall() to possibly output characters

This kind of code is often used to execute a tiny self-contained language or generate output from a compressed string.

---

Likely Behavior When Run

If you compile and run this with:

./a.out 'encoded_string'

It would process each character, updating memory and maybe writing output to stdout using syscall(4, ...) — which is a direct write system call on Unix/Linux.

---

TL;DR

This code:

• Takes a command-line string
• Interprets each character with custom logic
• Modifies a buffer
• Possibly outputs characters via syscall
• Uses heavy recursion and obfuscation tricks

It’s likely an interpreter or decoder, possibly producing ASCII art or executing some esoteric code. Would you like me to deobfuscate and rewrite it clearly?

Edit: had to get GPT to reveal the original markdown ina code block so it had to escape the ``` with \```

how te fook. (also who is here from bf in 100 seconds)

Me lol