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;}

After a few back and forth with GPT-4o, I got this:

#include <unistd.h>  // for syscall

#define MEMORY_SIZE 99
#define SYSCALL_WRITE 4

#define INCREMENT '+'
#define DECREMENT '-'
#define SHIFT_RIGHT '>'
#define SHIFT_LEFT '<'
#define OUTPUT '.'
#define INPUT ','
#define LOOP_START '['
#define LOOP_END ']'

#define IO_OPERATION_FLAG 2

#define TO_CHAR(x) ((char)(x))
#define TO_INT(x) ((int)(x))

char memory[MEMORY_SIZE], *pointer = memory, *return_address, command;

int main(char argument, char **arguments) {
    return_address = arguments;
    char *code = return_address[1];
    
    while ((command = TO_CHAR(*code++)) != '\0') {
        command = TO_CHAR(TO_INT(command) % 93);

        char is_io_operation = TO_CHAR(command & IO_OPERATION_FLAG);
        char is_pointer_operation = TO_CHAR(command % 7);

        if (is_pointer_operation) {
            if (argument) {
                if (command == INCREMENT || command == DECREMENT) {
                    if (command == INCREMENT) {
                        *pointer += INCREMENT - '0';
                    } else {
                        *pointer += DECREMENT + '0';
                    }
                } else if (command == SHIFT_RIGHT || command == SHIFT_LEFT) {
                    if (command == SHIFT_RIGHT) {
                        pointer += SHIFT_RIGHT - '>';
                    } else {
                        pointer += SHIFT_LEFT - '<';
                    }
                } else if (command == OUTPUT || command == INPUT) {
                    syscall(SYSCALL_WRITE - !is_io_operation, is_io_operation, pointer, 1);
                }
            }
        } else {
            code = return_address;  // Set code pointer back to the start of the current command
        }

        while (is_io_operation && (command | argument ** pointer)) {
            code = return_address;
            main(!command, &argument);  // Toggle argument based on the command
        }

        return_address = code;
    }

    return 0;
}

Wow. wow.

To any newcomers:

Compile using gcc with the flag "-m32"

You may need to install the gcc-multilib package in order to target an x86 binary

After you have the right libraries installed, you should be able to compile like this:

gcc -m32 -o bf bf.c

Cheers!

Og code using an online C beautifier: https://codebeautify.org/c-formatter-beautifier/y255f5fa5

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;
}