plabble_codec/codec/common/
dyn_int.rs

1use crate::abstractions::SerializationError;
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
53pub fn read_from_slice(data: &[u8]) -> Result<(u128, usize), SerializationError> {
54    let mut idx = 0;
55    loop {
56        if idx > data.len() - 1 {
57            break Err(SerializationError::TooFewBytes(1));
58        }
59
60        if (data[idx] & 1 << 7) == 0 {
61            break Ok((decode(&data[..=idx]), idx + 1));
62        }
63
64        idx += 1;
65    }
66}
67
68#[cfg(test)]
69mod test {
70    use super::*;
71
72    #[test]
73    fn can_encode_decode_number() {
74        let number = 1234567890;
75        let encoded = encode(number);
76        let decoded = decode(&encoded);
77        assert_eq!(number, decoded);
78        assert_eq!(5, encoded.len()); // 1234567890 ~ 2^31, 7 bits per byte = 7 * 5 = 35
79    }
80
81    #[test]
82    fn can_decode_number() {
83        let nr = &[216u8, 4];
84        let res = decode(nr);
85        assert_eq!(600, res);
86    }
87
88    #[test]
89    fn can_decode_number_from_larger_slice() {
90        let nr = &[216u8, 4, 234, 19, 74];
91        let res = read_from_slice(nr).unwrap();
92        assert_eq!((600, 2), res);
93    }
94
95    #[test]
96    fn can_decode_number_in_4_bytes() {
97        let max_nr = 268435455; // max number in 4 bytes
98        let encoded = encode(max_nr);
99        assert_eq!(4, encoded.len());
100    }
101
102    #[test]
103    fn cant_decode_bignr_in_4_bytes() {
104        let max_nr = 268435456;
105        let encoded = encode(max_nr);
106        assert_ne!(4, encoded.len());
107    }
108
109    #[test]
110    fn cant_decode_slice_that_lies() {
111        let slice = &[0b10111110]; // slice notes there is a second byte (7th bit, right-to-left), but there's not
112        let decoded = read_from_slice(slice);
113        assert!(decoded.is_err());
114    }
115
116    #[test]
117    fn can_encode_nr_lt_128_in_1_byte() {
118        let encoded = encode(127);
119        assert_eq!(1, encoded.len());
120    }
121
122    #[test]
123    fn can_guess_encoded_size() {
124        let one_byte = 127;
125        assert_eq!(1, encoded_size(one_byte));
126
127        let two_bytes = 128;
128        assert_eq!(2, encoded_size(two_bytes));
129
130        let four_bytes = 268435455;
131        assert_eq!(4, encoded_size(four_bytes));
132    }
133}
plabble_codec/codec/common/dyn_int.rs

plabble_codec/codec/common/
dyn_int.rs
