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pub mod utils;
pub mod options;
fn num_size(n: u64) -> u64 {
if n < 10 {
1
} else {
1 + num_size(n / 10)
}
}
fn calculate_shift(number: u64, size: u64, position: u64) -> u64 {
let actual_position = (position % size) + 1;
let exponent = (size - actual_position) as u32;
(number / 10u64.pow(exponent)) % 10
}
fn encode_byte(c: u8, key: u64, shift: u64) -> u64 {
let mut nc = c as u64 + shift;
nc *= key;
nc += key;
nc *= key;
nc - 2 * key
}
fn decode_byte(c: u64, key: u64, shift: u64) -> u8 {
let mut nc = c;
nc += 2 * key;
nc /= key;
nc -= key;
nc /= key;
(nc - shift) as u8
}
pub fn encode(characters: Vec<u8>, key: u64) -> Vec<u64> {
let key_size = num_size(key);
let shifts = (0..key_size)
.cycle()
.map(|i| calculate_shift(key, key_size, i));
characters.into_iter()
.zip(shifts)
.map(|(c, shift)| encode_byte(c, key, shift))
.collect::<Vec<u64>>()
}
pub fn decode(numbers: Vec<u64>, key: u64) -> String {
let key_size = num_size(key);
let shifts = (0..key_size)
.cycle()
.map(|i| calculate_shift(key, key_size, i));
let bytes = numbers.into_iter()
.zip(shifts)
.map(|(c, shift)| decode_byte(c as u64, key, shift))
.collect::<Vec<u8>>();
String::from_utf8(bytes).unwrap()
}
#[cfg(test)]
mod tests {
use super::num_size;
use super::calculate_shift;
#[test]
fn test_num_size() {
assert_eq!(num_size(1234), 4);
assert_eq!(num_size(345342), 6);
}
#[test]
fn test_calculate_shift() {
let n = 1235;
let size = num_size(n);
assert_eq!(calculate_shift(n, size, 0), 1);
assert_eq!(calculate_shift(n, size, 7), 5);
}
}