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/*
* Copyright 2019 Reiner Herrmann <reiner@reiner-h.de>
* License: GPL-3+
*/
use std::env;
use std::fs::File;
use std::io::{self, Read, BufReader};
use std::collections::HashMap;
#[derive(PartialEq,Debug)]
enum Command {
INCPTR,
DECPTR,
INCVAL,
DECVAL,
PUTC,
GETC,
LOOPSTART { end: usize },
LOOPEND { start: usize },
}
struct Program {
commands: Vec<Command>,
}
impl Program {
pub fn run(&mut self, input: &mut dyn io::Read, output: &mut dyn io::Write) -> Result<(), String> {
let mut memory : HashMap<isize, u8> = HashMap::new();
let mut pos : isize = 0;
let mut pc : usize = 0;
loop {
if pc >= self.commands.len() {
break;
}
match self.commands[pc] {
Command::INCPTR => pos = pos.checked_add(1).ok_or("Pointer overflow")?,
Command::DECPTR => pos = pos.checked_sub(1).ok_or("Pointer underflow")?,
Command::INCVAL => {
let val = memory.entry(pos).or_insert(0);
*val = val.wrapping_add(1);
},
Command::DECVAL => {
let val = memory.entry(pos).or_insert(0);
*val = val.wrapping_sub(1);
},
Command::PUTC => {
let char_out = *memory.get(&pos).unwrap_or(&0);
output.write(&[char_out]).or(Err("Writing to output failed"))?;
},
Command::GETC => {
let mut char_in = [0];
input.read_exact(&mut char_in).or(Err("Reading the input failed"))?;
memory.insert(pos, char_in[0]);
},
Command::LOOPSTART { end } => {
if *memory.get(&pos).unwrap_or(&0) == 0 {
pc = end;
}
},
Command::LOOPEND { start } => {
pc = start;
continue;
},
};
pc = pc.checked_add(1).ok_or("PC overflow")?;
}
Ok(())
}
}
fn read_program(filename: &str) -> Result<String, io::Error> {
let file = File::open(filename)?;
let mut content = String::new();
let mut reader = BufReader::new(file);
reader.read_to_string(&mut content)?;
Ok(content)
}
fn find_loops(commands: &mut Vec<Command>) -> Result<(), String> {
let mut loop_starts = Vec::new();
for i in 0 .. commands.len() {
match commands[i] {
Command::LOOPSTART { .. } => {
loop_starts.push(i);
}
Command::LOOPEND { .. } => {
let start = loop_starts.pop().ok_or("Cannot find opening bracket for closing bracket")?;
commands[start] = Command::LOOPSTART { end: i };
commands[i] = Command::LOOPEND { start };
},
_ => {},
};
}
if !loop_starts.is_empty() {
return Err("More opening than closing loop brackets".to_string());
}
Ok(())
}
fn preprocess(program: &str) -> String {
let allowed_chars = ['>', '<', '+', '-', '.', ',', '[', ']'];
program.chars().filter(|c| allowed_chars.contains(c)).collect()
}
fn tokenize(input: &str) -> Vec<Command> {
input.chars().map(|token|
match token {
'>' => Command::INCPTR,
'<' => Command::DECPTR,
'+' => Command::INCVAL,
'-' => Command::DECVAL,
'.' => Command::PUTC,
',' => Command::GETC,
'[' => Command::LOOPSTART { end: 0 },
']' => Command::LOOPEND { start: 0 },
_ => panic!("Trying to tokenize invalid character: {}", token),
}
).collect()
}
fn run() -> Result<(), String> {
let args: Vec<String> = env::args().collect();
if args.len() < 2 {
return Err(format!("Usage: {} filename", args[0]));
}
let input = match read_program(&args[1]) {
Ok(p) => preprocess(&p),
Err(e) => return Err(format!("Cannot open file: {}", e)),
};
let mut commands = tokenize(&input);
find_loops(&mut commands)?;
let mut program = Program{commands};
program.run(&mut io::stdin(), &mut io::stdout())
}
fn main() {
if let Err(e) = run() {
println!("Error: {}", e);
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_preprocess() {
assert_eq!(preprocess(">foo<bar[hello] world. this,is+a-comment"), "><[].,+-");
assert_eq!(preprocess(""), "");
assert_eq!(preprocess("not a real program"), "");
assert_eq!(preprocess("[>>>+++,---.<<<]"), "[>>>+++,---.<<<]");
}
#[test]
fn test_tokenize() {
assert_eq!(tokenize(""), []);
assert_eq!(tokenize("><+-.,[]"),
[
Command::INCPTR,
Command::DECPTR,
Command::INCVAL,
Command::DECVAL,
Command::PUTC,
Command::GETC,
Command::LOOPSTART { end: 0 },
Command::LOOPEND { start: 0 },
]
);
}
#[test]
#[should_panic]
fn test_tokenize_panic() {
tokenize("42");
}
#[test]
fn test_find_loops() {
let mut commands = vec![
Command::INCPTR,
Command::INCVAL,
Command::LOOPSTART { end: 0 },
Command::DECPTR,
Command::LOOPSTART { end: 0 },
Command::DECVAL,
Command::LOOPEND { start: 0 },
Command::PUTC,
Command::LOOPEND { start: 0 },
];
assert!(find_loops(&mut commands).is_ok());
assert_eq!(commands[2], Command::LOOPSTART { end: 8 });
assert_eq!(commands[4], Command::LOOPSTART { end: 6 });
assert_eq!(commands[6], Command::LOOPEND { start: 4 });
assert_eq!(commands[8], Command::LOOPEND { start: 2 });
}
#[test]
fn test_find_loop_unbalanced() {
let mut commands = vec![Command::INCPTR, Command::LOOPSTART { end: 0 }, Command::INCVAL];
assert!(find_loops(&mut commands).is_err());
let mut commands = vec![Command::INCPTR, Command::LOOPEND { start: 0 }, Command::INCVAL];
assert!(find_loops(&mut commands).is_err());
}
#[test]
fn test_program_run() {
use std::io::Cursor;
let mut buf_in = Cursor::new("31abc".as_bytes());
let mut buf_out = Cursor::new(Vec::new());
let code = "++[>[>],+[<]>-]>[.>]"; // reads 2 chars, increments them, and prints them at the end
let mut commands = tokenize(code);
find_loops(&mut commands).unwrap();
let mut program = Program{commands};
program.run(&mut buf_in, &mut buf_out).unwrap();
let expected = vec!['4' as u8, '2' as u8];
assert_eq!(buf_out.get_ref(), &expected);
}
}
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