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

fn fold_size<R>(
    mut size: u8,
    f: &mut FnMut(u8, u8, R) -> std::io::Result<R>,
    mut result: R
) -> std::io::Result<R> {
    let mut offset = 0;
    while size >= 8 {
        result = f(offset, 8, result)?;
        offset += 8;
        size -= 8;
    }
    if size > 0 {
        result = f(offset, size, result)?;
    }
    Ok(result)
}

pub trait BitWrite {
    fn write(&mut self, value: u8, size: u8) -> std::io::Result<()>;
    // Little-endian.
    fn write32(&mut self, value: u32, size: u8) -> std::io::Result<()> {
        fold_size(
            size,
            &mut |o, s, _| self.write((value >> o) as u8, s),
            ()
        )
    }
}

pub trait BitRead {
    fn read(&mut self, size: u8) -> std::io::Result<u8>;
    // Little-endian.
    fn read32(&mut self, size: u8) -> std::io::Result<u32> {
        fold_size(
            size,
            &mut |o, s, r| Ok(r | ((self.read(s)? as u32) << o)),
            0
        )
    }
}

struct BitWriteAdapter<'t> {
    w: &'t mut std::io::Write,
    buffer: u8,
    // 0..7
    size: u8,
}

impl<'t> BitWriteAdapter<'t> {
    fn flush(&mut self) -> std::io::Result<()> {
        self.w.write_all(&[self.buffer])
    }
}

impl<'t> BitWrite for BitWriteAdapter<'t> {
    // size is in [0..8]
    fn write(&mut self, value: u8, size: u8) -> std::io::Result<()> {
        self.buffer |= value << self.size;
        self.size += size;
        if self.size >= 8 {
            self.flush()?;
            self.size -= 8;
            self.buffer = value >> (size - self.size)
        }
        Ok(())
    }
}

/// Creates a `BitWrite` object and pass it to the given scope function `f`.
///
/// ```
/// let mut v = vec![];
/// {
///     let mut c = std::io::Cursor::new(&mut v);
///     bitrw::with_bit_writer(&mut c, &mut |w| {
///         w.write(0, 0); //  0
///         w.write(1, 1); //  1
///         w.write(2, 2); //  3
///         w.write(3, 3); //  6
///         w.write(4, 4); // 10
///         w.write(5, 5); // 15
///         w.write(6, 6); // 21
///         Ok(())
///     });
/// }
/// assert_eq!(v, [0b00_011_10_1, 0b0_00101_01, 0b00011]);
/// ```
pub fn with_bit_writer<R>(
    w: &mut std::io::Write,
    f: &mut Fn(&mut BitWrite) -> std::io::Result<R>
) -> std::io::Result<R> {
    let mut adapter = BitWriteAdapter { w: w, buffer: 0, size: 0 };
    let result = f(&mut adapter)?;
    if adapter.size > 0 {
        adapter.flush()?;
    }
    Ok(result)
}

/// Provides `BitRead` from a `Read`.
///
/// ```
/// use bitrw::BitRead;
/// let mut c = std::io::Cursor::new(&[0b00_11_10_1_0, 0b1_110_101_1, 0b1101000]);
/// let mut r = bitrw::BitReadAdapter::new(&mut c);
/// assert_eq!(r.read(0).unwrap(), 0);
/// assert_eq!(r.read(1).unwrap(), 0);
/// assert_eq!(r.read(1).unwrap(), 1);
/// assert_eq!(r.read(2).unwrap(), 2);
/// assert_eq!(r.read(2).unwrap(), 3);
/// assert_eq!(r.read(3).unwrap(), 4);
/// assert_eq!(r.read(3).unwrap(), 5);
/// assert_eq!(r.read(3).unwrap(), 6);
/// assert_eq!(r.read(8).unwrap(), 0b11010001);
/// ```
pub struct BitReadAdapter<'t> {
    r: &'t mut std::io::Read,
    buffer: u8,
    // 0..7
    size: u8,
}

impl<'t> BitReadAdapter<'t> {
    pub fn new(r: &'t mut std::io::Read) -> Self {
        Self { r: r, buffer: 0, size: 0 }
    }
}

impl<'t> BitRead for BitReadAdapter<'t> {
    fn read(&mut self, size: u8) -> std::io::Result<u8> {
        let b16 = if self.size >= size {
            self.buffer as u16
        } else {
            let mut b = [0];
            self.r.read_exact(&mut b)?;
            let result = ((b[0] as u16) << self.size) | (self.buffer as u16);
            self.size += 8;
            result
        };
        self.size -= size;
        self.buffer = (b16 >> size) as u8;
        Ok((b16 & base2::mask(size) as u16) as u8)
    }
}