zrip-core 0.2.0

Shared types and codecs for zrip (internal crate)
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
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

#[cfg(feature = "alloc")]
use alloc::vec::Vec;

pub struct BitWriter {
    #[cfg(feature = "alloc")]
    buf: Vec<u8>,
    bits: u64,
    bits_used: u8,
    pos: usize,
}

#[cfg(feature = "alloc")]
impl BitWriter {
    pub fn new() -> Self {
        Self {
            buf: Vec::with_capacity(64),
            bits: 0,
            bits_used: 0,
            pos: 0,
        }
    }

    pub fn with_capacity(cap: usize) -> Self {
        Self {
            buf: Vec::with_capacity(cap + 8),
            bits: 0,
            bits_used: 0,
            pos: 0,
        }
    }

    pub fn from_vec(mut buf: Vec<u8>) -> Self {
        buf.clear();
        buf.reserve(8);
        Self {
            buf,
            bits: 0,
            bits_used: 0,
            pos: 0,
        }
    }

    pub fn into_vec(mut self) -> Vec<u8> {
        self.flush_remaining();
        self.buf
    }

    #[inline(always)]
    fn ensure_capacity(&mut self) {
        if self.pos + 8 > self.buf.capacity() {
            unsafe {
                self.buf.set_len(self.pos);
            }
            self.buf.reserve(64);
        }
    }

    #[inline(always)]
    pub fn write_bits(&mut self, value: u32, n: u8) {
        debug_assert!(n <= 25);
        if n == 0 {
            return;
        }
        debug_assert!(value < (1u32 << n));
        self.bits |= (value as u64) << self.bits_used;
        self.bits_used += n;
        if self.bits_used >= 32 {
            self.ensure_capacity();
            unsafe {
                let ptr = self.buf.as_mut_ptr().add(self.pos);
                (ptr as *mut u64).write_unaligned(self.bits.to_le());
                let nb = (self.bits_used >> 3) as usize;
                self.pos += nb;
                self.bits >>= nb << 3;
                self.bits_used &= 7;
            }
        }
    }

    pub fn flush_remaining(&mut self) {
        unsafe {
            self.buf.set_len(self.pos);
        }
        while self.bits_used > 0 {
            self.buf.push(self.bits as u8);
            self.bits >>= 8;
            self.bits_used = self.bits_used.saturating_sub(8);
        }
        self.pos = self.buf.len();
    }

    pub fn close_reverse_stream(&mut self) {
        self.write_bits(1, 1);
        self.flush_remaining();
    }

    pub fn bits_written(&self) -> usize {
        self.pos * 8 + self.bits_used as usize
    }

    pub fn into_bytes(mut self) -> Vec<u8> {
        self.flush_remaining();
        self.buf
    }

    pub fn as_bytes(&mut self) -> &[u8] {
        unsafe {
            self.buf.set_len(self.pos);
        }
        &self.buf
    }

    pub fn write_byte(&mut self, b: u8) {
        self.write_bits(b as u32, 8);
    }

    pub fn write_bytes(&mut self, bytes: &[u8]) {
        for &b in bytes {
            self.write_byte(b);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn write_and_read_back() {
        let mut w = BitWriter::new();
        w.write_bits(0b101, 3);
        w.write_bits(0b11, 2);
        w.write_bits(0b000, 3);
        let bytes = w.into_bytes();
        assert_eq!(bytes, [0b00011101]);
    }

    #[test]
    fn write_cross_byte() {
        let mut w = BitWriter::new();
        w.write_bits(0xFF, 8);
        w.write_bits(0x01, 8);
        let bytes = w.into_bytes();
        assert_eq!(bytes, [0xFF, 0x01]);
    }

    #[test]
    fn write_partial() {
        let mut w = BitWriter::new();
        w.write_bits(0b1, 1);
        let bytes = w.into_bytes();
        assert_eq!(bytes, [0b00000001]);
    }

    #[test]
    fn reverse_stream_roundtrip() {
        use crate::bitstream::reader_reverse::ReverseBitReader;

        let mut w = BitWriter::new();
        w.write_bits(0b1010, 4);
        w.write_bits(0b0101, 4);
        w.close_reverse_stream();
        let bytes = w.into_bytes();

        let mut r = ReverseBitReader::new(&bytes).unwrap();
        assert_eq!(r.read_bits(4).unwrap(), 0b0101);
        assert_eq!(r.read_bits(4).unwrap(), 0b1010);
        assert_eq!(r.bits_remaining(), 0);
    }
}