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const PROGRAM_NAME: &str = "xor_compress";
fn read_files(filenames: &[String]) -> Result<Vec<u8>, (&String, std::io::Error)> {
let mut data = Vec::new();
for filename in filenames.iter() {
match std::fs::read(filename) {
Ok(bytes) => data.extend(&bytes),
Err(err) => return Err((filename, err)),
}
}
Ok(data)
}
fn write_compressed(filename: &String, data: Vec<u8>) -> Result<u32, std::io::Error> {
let n = data.len();
let mut output = Vec::new();
let mut v = 0x00;
let mut i = 0;
let mut runs = 0;
while i < n {
let mut byte = data[i];
i += 1;
runs += 1;
if data[i] == v {
// Alternating (>= 0x80)
// Run stops at 0x80 bytes or when the values stop alternating
let mut size = 0;
while i < n && size < 0x80 && data[i] == (if size % 2 == 0 { v } else { byte }) {
size += 1;
i += 1;
}
output.push(size + 0x7f);
output.push(v ^ byte);
if size % 2 == 0 {
v = byte;
}
} else {
// Sequential (< 0x80)
// Run stops at 0x80 bytes or when the value two ahead is equal to v
let mut buffer = vec![v ^ byte];
while i < n {
v = byte;
if buffer.len() > 0x7f || (i + 1 < n && data[i + 1] == v) {
break;
}
byte = data[i];
buffer.push(v ^ byte);
i += 1;
}
output.push((buffer.len() - 1) as u8);
output.extend(buffer);
}
}
match std::fs::write(filename, &output[..]) {
Ok(()) => Ok(runs),
Err(err) => Err(err),
}
}
fn main() {
let mut args: Vec<String> = std::env::args().skip(1).collect();
let mut verbose = false;
if !args.is_empty() && args[0] == "-v" {
verbose = true;
args.remove(0);
}
if args.len() < 2 {
eprintln!("Usage: {} [-v] file... files.xor", PROGRAM_NAME);
std::process::exit(1);
}
let out_filename = args.pop().unwrap();
let data = match read_files(&args[..]) {
Ok(data) => data,
Err((filename, err)) => {
eprintln!("{}: {}: {}", PROGRAM_NAME, filename, err);
std::process::exit(err.raw_os_error().unwrap_or(1));
}
};
if !data.is_empty() {
match write_compressed(&out_filename, data) {
Ok(runs) => if verbose {
println!("{}: {}: ld bc, ${:x}", PROGRAM_NAME, out_filename, runs);
},
Err(err) => {
eprintln!("{}: {}: {}", PROGRAM_NAME, out_filename, err);
std::process::exit(err.raw_os_error().unwrap_or(1));
},
}
}
}
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