libstomper 0.2.0

Library for stomper compression tool
Documentation 
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

//! Tool for reading bits one by one from stream

use std::io::Read;

const BUFFER_SIZE: usize = 128;

pub struct BitReader<R: Read> {
    reader: R,
    buffer: [u8; BUFFER_SIZE],
    end: usize,
    bytecount: usize,
    bitpos: usize,
}

impl <R: Read> BitReader<R> {

    /// Returns new bitreader and takes ownership of given reader
    pub fn new(reader: R) -> Self {
        let mut bitreader = BitReader {
            reader,
            buffer: [0; BUFFER_SIZE],
            end: 0,
            bytecount: 0,
            bitpos: 0,
        };
        bitreader.read_to_buffer();
        bitreader
    } 

    /// Return next bit in the stream and None reached end of file. True represent 1 and false 0
    pub fn next_bit(&mut self) -> Option<bool> {
        // Read more bytes if buffer is full
        if self.bytecount > BUFFER_SIZE - 1 {
            self.read_to_buffer();
        }

        // Returns none if reached EOF
        if self.bytecount == self.end  && self.read_to_buffer() == 0 {
            return None
        };

        let next = self.buffer[self.bytecount];
        let mask = 1 << self.bitpos;
        self.bitpos += 1;
        if self.bitpos > 7 {
            self.bytecount += 1;
            self.bitpos = 0;
        }
        if next & mask != 0 {
            Some(true)
        } else {
            Some(false)
        }
    }    

    /// Reads bytes from the underlying reader to buffer
    fn read_to_buffer(&mut self) -> usize {
        self.end = self.reader.read(&mut self.buffer).expect("Could not read to buffer");
        self.bytecount = 0;
        self.bitpos = 0;
        self.end
    }
}

#[cfg(test)]
mod tests {
    use super::BitReader;
    #[test]
    fn reader_reads_correctly_no1() {
        let mut v = Vec::new();
        v.push(0b10110011);
        let mut reader = BitReader::new(v.as_slice());
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), None);
    }

    #[test]
    fn reader_reads_correctly_no2() {
        let mut v = Vec::new();
        v.push(0b10110011);
        v.push(0b11110000);
        v.push(0b00110011);
        let mut reader = BitReader::new(v.as_slice());
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(true));
        

        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        
        
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(true));
        assert_eq!(reader.next_bit(), Some(false));
        assert_eq!(reader.next_bit(), Some(false));

        assert_eq!(reader.next_bit(), None) 
    }

    #[test]
    fn reader_reads_till_end() {
        let mut v: Vec<u8> = Vec::new();
        let bytes = 20000; 
        let bits = bytes * 8;
        for _i in 0..bytes {
            v.push(21);
        }
        let mut bits_read = 0;
        let mut reader = BitReader::new(v.as_slice());
        while let Some(_bit) = reader.next_bit() {
            bits_read += 1;
        }
        assert_eq!(bits, bits_read);
    }
}