brainfuck.c

//compiles to 740 bytes using -O0, 384 bytes using -Os
//both targeting i386 and with freestanding GCC compiler

typedef unsigned int size_t;




void interpret(volatile char* s, int s_size, volatile char* input, volatile char* output){
    int i=0;
    int right = s_size;
    size_t ptr;
    int BUFSIZE = 1000;
    char buf[BUFSIZE];
    int inpos=0;
    int outpos=0;
    while ( i < right){
        switch(s[i]){
            case '>':
            {
                ptr++;
                if(ptr >= BUFSIZE){
                    ptr = 0;
                }
                break;
            }
            case '<':
            {
                ptr--;
                if(ptr < 0){
                    ptr = BUFSIZE - 1;
                }
                break;
            }
            case '.':
                buf[ptr] = input[inpos];
                inpos++;
                break;
            case '+':
                buf[ptr]++;
                break;
            case '-':
                buf[ptr]--;
                break;
            case '[':
            {
                int loop = 1;
                while(loop > 0){
                    i++;
                    char c = s[i];
                    if(c == '['){
                        loop++;
                    }else if(c == ']'){
                        loop--;
                    }
                }
                break;
            }
            case ']':
            {
                int loop = 1;
                while(loop > 0){
                    i--;
                    char c = s[i];
                    if(c == '['){
                        loop--;
                    }else if(c == ']'){
                        loop++;
                    }
                }
                i--;
                break;
            }
            case ',':
                output[outpos] = buf[ptr];
                outpos++;
                break;
        }
        i++;
    }
}


void start() __attribute__((section(".text.start")));
void start(){
    //use volatile pointers here so the compiler doesn't assume the memory is empty
    start((volatile char*)0x1000, 1000, (volatile char*)0x2000, (volatile char*)0x3000);
}