binary_codec/
dyn_int.rs

1use crate::DeserializationError;
2
3/// Gives encoded size in bytes
4///
5/// # Arguments
6/// * `nr` - number to encode
7pub fn encoded_size(nr: u128) -> usize {
8    let mut res = 0;
9    let mut nr = nr;
10    while nr > 0 {
11        nr /= 128;
12        res += 1;
13    }
14    res
15}
16
17/// Encodes a number into a vector of bytes.
18///
19/// # Arguments
20/// * `nr` - number to encode
21pub fn encode(nr: u128) -> Vec<u8> {
22    let mut res = Vec::new();
23    let mut nr = nr;
24    while nr > 0 {
25        let mut encoded = nr % 128;
26        nr /= 128;
27        if nr > 0 {
28            encoded |= 128;
29        }
30        res.push(encoded as u8);
31    }
32    res
33}
34
35/// Decodes a number from a slice of bytes.
36///
37/// # Arguments
38/// * `data` - slice of bytes to decode
39pub fn decode(data: &[u8]) -> u128 {
40    let mut num = 0;
41    let mut multiplier = 1;
42    for byte in data {
43        num += (*byte as u128 & 127) * multiplier;
44        multiplier *= 128;
45    }
46    num
47}
48
49/// Decodes a number from a slice of bytes when size of encoded number is unknown, returning the number and the number of bytes read.
50///
51/// # Arguments
52/// * `data` - slice of bytes to decode number from
53///
54/// # Returns
55/// * (number, bytes read)
56pub fn read_from_slice(data: &[u8]) -> Result<(u128, usize), DeserializationError> {
57    let mut idx = 0;
58    loop {
59        if idx > data.len() - 1 {
60            break Err(DeserializationError::NotEnoughBytes(1));
61        }
62
63        if (data[idx] & 1 << 7) == 0 {
64            break Ok((decode(&data[..=idx]), idx + 1));
65        }
66
67        idx += 1;
68    }
69}
70
71#[cfg(test)]
72mod test {
73    use super::*;
74
75    #[test]
76    fn can_encode_decode_number() {
77        let number = 1234567890;
78        let encoded = encode(number);
79        let decoded = decode(&encoded);
80        assert_eq!(number, decoded);
81        assert_eq!(5, encoded.len()); // 1234567890 ~ 2^31, 7 bits per byte = 7 * 5 = 35
82    }
83
84    #[test]
85    fn can_decode_number() {
86        let nr = &[216u8, 4];
87        let res = decode(nr);
88        assert_eq!(600, res);
89    }
90
91    #[test]
92    fn can_decode_number_from_larger_slice() {
93        let nr = &[216u8, 4, 234, 19, 74];
94        let res = read_from_slice(nr).unwrap();
95        assert_eq!((600, 2), res);
96    }
97
98    #[test]
99    fn can_decode_number_in_4_bytes() {
100        let max_nr = 268435455; // max number in 4 bytes
101        let encoded = encode(max_nr);
102        assert_eq!(4, encoded.len());
103    }
104
105    #[test]
106    fn cant_decode_bignr_in_4_bytes() {
107        let max_nr = 268435456;
108        let encoded = encode(max_nr);
109        assert_ne!(4, encoded.len());
110    }
111
112    #[test]
113    fn cant_decode_slice_that_lies() {
114        let slice = &[0b10111110]; // slice notes there is a second byte (7th bit, right-to-left), but there's not
115        let decoded = read_from_slice(slice);
116        assert!(decoded.is_err());
117    }
118
119    #[test]
120    fn can_encode_nr_lt_128_in_1_byte() {
121        let encoded = encode(127);
122        assert_eq!(1, encoded.len());
123    }
124
125    #[test]
126    fn can_guess_encoded_size() {
127        let one_byte = 127;
128        assert_eq!(1, encoded_size(one_byte));
129
130        let two_bytes = 128;
131        assert_eq!(2, encoded_size(two_bytes));
132
133        let four_bytes = 268435455;
134        assert_eq!(4, encoded_size(four_bytes));
135    }
136}
binary_codec/dyn_int.rs

binary_codec/
dyn_int.rs
