br4infuck 0.1.5

A brainfuck interpreter
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151

use std;
use std::fs::OpenOptions;
use std::io::{self, Read, Write};

// Interpret brainfuck code
pub fn evaluate(program: String) {
    let tape_length = 30_000;

    let mut buffer = String::new();

    let mut tape: Vec<u8> = vec![0; tape_length];
    let mut ptr = 0;
    let mut is_looping = false;
    let mut loop_stack = vec![];
    let mut inner_loops = 0;

    let mut i = 0;

    while i < program.len() {
        let c = program.chars().nth(i).unwrap();

        if is_looping {
            if c == '[' {
                inner_loops += 1;
            }
            if c == ']' {
                if inner_loops == 0 {
                    is_looping = false;
                } else {
                    inner_loops -= 1;
                }
            }

            i += 1;
            continue;
        }

        match c {
            '+' => tape[ptr] += 1,
            '-' => tape[ptr] -= 1,
            '>' => {
                ptr += 1;
            }
            '<' => {
                ptr -= 1;
            }
            '.' => {
                print!("{}", tape[ptr] as char);
                io::stdout().flush();
            }
            ',' => {
                io::stdin().read_to_string(&mut buffer);
                tape[ptr] = buffer.chars().next().unwrap() as u8;
            }
            ']' => {
                if tape[ptr] != 0 {
                    i = loop_stack[loop_stack.len() - 1];
                } else {
                    loop_stack.pop();
                }
            }
            '[' => {
                if tape[ptr] == 0 {
                    is_looping = true;
                } else {
                    loop_stack.push(i);
                }
            }
            _ => {}
        }

        i += 1;
    }
}

// compile brainfuck code to x86
pub fn compile(program: String) {

    let mut file = OpenOptions::new()
        .write(true)
        .create(true)
        .open("temp.s")
        .unwrap();

    let mut matching_bracket;

    let mut num_brackets = 0;
    let mut loop_stack = vec![];
    let prologue = concat!(
        ".text\n",
        ".globl _main\n",
        "_main:\n",
        "  pushq %rbp\n",
        "  movq %rsp, %rbp\n",
        "  pushq %r12\n",        // store callee saved register
        "  subq $30008, %rsp\n", // allocate 30,008 B on stack, and realign
        "  leaq (%rsp), %rdi\n", // address of beginning of tape
        "  movl $0, %esi\n",     // fill with 0's
        "  movq $30000, %rdx\n", // length 30,000 B
        "  call _memset\n",      // memset
        "  movq %rsp, %r12\n",
        "\n",
    );

    file.write_all(prologue.as_bytes());

    let mut i = 0;
    while i < program.len() {
        let c = program.chars().nth(i).unwrap();

        match c {
            '+' => { file.write_all(b"  incb (%r12)\n"); },
            '-' => { file.write_all(b"  decb (%r12)\n"); },
            '>' => { file.write_all(b"  inc %r12\n"); },
            '<' => { file.write_all(b"  dec %r12\n"); },
            '.' => {
                // move byte to double word and zero upper bits since putchar takes an int.
                file.write_all(b"  movzbl (%r12), %edi\n");
                file.write_all(b"  call _putchar\n");
            }
            ',' => {
                file.write_all(b"  call _getchar\n");
                file.write_all(b"  movb %al, (%r12)\n");
            }
            ']' => {
                matching_bracket = loop_stack.pop().unwrap(); // Should check if stack underflow
                file.write_all(b"  cmpb $0, (%r12)\n");
                file.write_all(format!("  jne bracket_{}_start\n", matching_bracket).as_bytes());
                file.write_all(format!("bracket_{}_end:\n", matching_bracket).as_bytes());
            }
            '[' => {
                loop_stack.push(num_brackets); // Should check if too much nesting
                file.write_all(b"  cmpb $0, (%r12)\n");
                file.write_all(format!("  je bracket_{}_end\n", num_brackets).as_bytes());
                file.write_all(format!("bracket_{}_start:\n", num_brackets).as_bytes());
                num_brackets += 1;
            }
            _ => {}
        }

        i += 1;
    }

    let epilogue = concat!(
        "  addq $30008, %rsp\n", // clean up tape from stack.
        "  popq %r12\n",         // restore callee saved register
        "  popq %rbp\n",
        "  ret\n"
    );
    file.write_all(epilogue.as_bytes());
}