1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
use std::iter::FromIterator;
#[derive(Clone, Eq, PartialEq, Hash, Debug)]
pub struct EncodingSchemeForm {
pub prefix: u64,
pub bit_count: u8,
pub prefix_length: u8,
}
#[derive(Clone, Eq, PartialEq, Debug)]
pub struct EncodingScheme {
bytes: Vec<u8>,
}
impl EncodingScheme {
pub fn new(bytes: Vec<u8>) -> EncodingScheme {
EncodingScheme { bytes: bytes }
}
pub fn bytes(&self) -> &Vec<u8> {
&self.bytes
}
pub fn into_bytes(self) -> Vec<u8> {
self.bytes
}
}
impl IntoIterator for EncodingScheme {
type Item = EncodingSchemeForm;
type IntoIter = EncodingSchemeIterator;
fn into_iter(self) -> EncodingSchemeIterator {
EncodingSchemeIterator { bytes: self.bytes, window: 0, bits_in_window: 0, bytes_offset: 0 }
}
}
#[derive(Debug)]
pub struct EncodingSchemeIterator {
bytes: Vec<u8>,
window: u64,
bits_in_window: u8,
bytes_offset: usize,
}
impl Iterator for EncodingSchemeIterator {
type Item = EncodingSchemeForm;
fn next(&mut self) -> Option<EncodingSchemeForm> {
while self.bits_in_window < 5+5+0b11111 {
let byte = *self.bytes.get(self.bytes_offset).unwrap_or(&0);
self.window = self.window + ((byte as u64) << self.bits_in_window);
self.bytes_offset += 1;
self.bits_in_window += 8;
}
if self.window == 0 {
None
}
else {
assert!(self.bytes_offset <= self.bytes.len()+(5+5+0b11111)/8);
let prefix_length = self.window as u8 & 0b11111;
self.window >>= 5;
self.bits_in_window -= 5;
let bit_count = self.window as u8 & 0b11111;
self.window >>= 5;
self.bits_in_window -= 5;
let prefix_mask = (0b1 << prefix_length) -1;
let prefix = self.window & prefix_mask;
self.window >>= prefix_length;
self.bits_in_window -= prefix_length;
Some(EncodingSchemeForm { prefix: prefix, bit_count: bit_count, prefix_length: prefix_length })
}
}
}
impl<'a> FromIterator<&'a EncodingSchemeForm> for EncodingScheme {
fn from_iter<T: IntoIterator<Item=&'a EncodingSchemeForm>>(forms: T) -> Self {
let mut bytes = Vec::<u8>::new();
let mut window = 0u64;
let mut bits_in_window = 0u8;
println!("---");
for form in forms {
assert!(form.prefix_length <= 0b11111);
assert!(form.bit_count <= 0b11111);
assert!(form.prefix < (1 << form.prefix_length));
window += (form.prefix as u64) << (5+5+bits_in_window);
window += (form.bit_count as u64) << (5+bits_in_window);
window += (form.prefix_length as u64) << (bits_in_window);
bits_in_window += 5+5+form.prefix_length;
while bits_in_window >= 8 {
bytes.push((window & 0b11111111) as u8);
window >>= 8;
bits_in_window -= 8;
}
}
if bits_in_window > 0 {
assert!(bits_in_window < 8);
assert!(window <= 0b11111111);
bytes.push(window as u8);
}
EncodingScheme::new(bytes)
}
}
#[cfg(test)]
mod tests {
use std::iter::FromIterator;
use super::*;
#[test]
fn test_trivial() {
let encoding = vec![0b011_00000, 0b00];
let forms = vec![EncodingSchemeForm { prefix: 0, bit_count: 3, prefix_length: 0 }];
assert_eq!(EncodingScheme::new(encoding.clone()).into_bytes(), encoding);
assert_eq!(EncodingScheme::from_iter(forms.iter()).into_bytes(), encoding);
assert_eq!(EncodingScheme::new(encoding.clone()).into_iter().collect::<Vec<_>>(), forms);
assert_eq!(EncodingScheme::from_iter(forms.iter()).into_iter().collect::<Vec<_>>(), forms);
}
#[test]
fn test_three() {
let encoding = b"\x4f\xf4\xff\x29\xd9\xff\x7f\x89\xee\xff\x07".to_vec();
let forms = vec![
EncodingSchemeForm {
prefix_length: 15,
bit_count: 2,
prefix: ((1<<15)-1) ^ (1<<1),
},
EncodingSchemeForm {
prefix_length: 20,
bit_count: 4,
prefix: ((1<<20)-1) ^ (1<<2),
},
EncodingSchemeForm {
prefix_length: 18,
bit_count: 8,
prefix: ((1<<18)-1) ^ (1<<3),
}
];
assert_eq!(EncodingScheme::new(encoding.clone()).into_bytes(), encoding);
assert_eq!(EncodingScheme::from_iter(forms.iter()).into_bytes(), encoding);
assert_eq!(EncodingScheme::new(encoding.clone()).into_iter().collect::<Vec<_>>(), forms);
assert_eq!(EncodingScheme::from_iter(forms.iter()).into_iter().collect::<Vec<_>>(), forms);
}
}