irox_bits/
bitstream.rs

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
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
// SPDX-License-Identifier: MIT
// Copyright 2024 IROX Contributors
//

use crate::{Bits, BitsError, BitsErrorKind, BitsWrapper, MutBits};
use core::cmp::Ordering;

pub struct BitStreamEncoder<'a, T: MutBits> {
    delegate: BitsWrapper<'a, T>,
    buf: u32,
    remaining: u8,
}
impl<'a, T: MutBits> Drop for BitStreamEncoder<'a, T> {
    fn drop(&mut self) {
        let [a, b, c, d] = self.buf.to_be_bytes();
        if self.remaining < 8 {
            // write 4
            let _ = self.delegate.write_all_bytes(&[a, b, c, d]);
        } else if self.remaining < 16 {
            // write 3
            let _ = self.delegate.write_all_bytes(&[a, b, c]);
        } else if self.remaining < 24 {
            // write 2
            let _ = self.delegate.write_all_bytes(&[a, b]);
        } else if self.remaining < 32 {
            // write 1
            let _ = self.delegate.write_u8(a);
        }
    }
}
impl<'a, T: MutBits> BitStreamEncoder<'a, T> {
    pub fn new(delegate: BitsWrapper<'a, T>) -> Self {
        Self {
            delegate,
            buf: 0u32,
            remaining: 32u8,
        }
    }
    pub fn write_u8_bits(&mut self, val: u8, num_bits: u8) -> Result<(), BitsError> {
        self.write_u32_bits(val as u32, num_bits)
    }
    pub fn write_u16_bits(&mut self, val: u16, num_bits: u8) -> Result<(), BitsError> {
        self.write_u32_bits(val as u32, num_bits)
    }
    pub fn write_u32_bits(&mut self, val: u32, mut num_bits: u8) -> Result<(), BitsError> {
        if num_bits > 32 {
            return Err(BitsErrorKind::InvalidInput.into());
        }
        while num_bits > 0 {
            match num_bits.cmp(&self.remaining) {
                Ordering::Less => {
                    let shift = self.remaining - num_bits;
                    let mask = (1u32 << num_bits) - 1;
                    self.buf |= (val & mask) << shift;
                    self.remaining -= num_bits;
                    num_bits = 0;
                }
                Ordering::Equal => {
                    let mask = (1u32 << num_bits) - 1;
                    self.buf |= val & mask;
                    num_bits = 0;
                    self.delegate.write_be_u32(self.buf)?;
                    self.remaining = 32;
                    self.buf = 0;
                }
                Ordering::Greater => {
                    let touse = self.remaining;
                    let shift = num_bits - self.remaining;
                    let mask = (1u32 << touse) - 1;
                    self.buf |= (val >> shift) & mask;
                    self.delegate.write_be_u32(self.buf)?;
                    self.remaining = 32;
                    self.buf = 0;
                    num_bits -= touse;
                }
            }
        }
        Ok(())
    }
}

pub struct BitStreamDecoder<'a, T: Bits> {
    delegate: BitsWrapper<'a, T>,
    buf: u32,
    used: u8,
}
impl<'a, T: Bits> BitStreamDecoder<'a, T> {
    pub fn new(delegate: BitsWrapper<'a, T>) -> Self {
        Self {
            delegate,
            buf: 0,
            used: 0,
        }
    }
    pub fn read_u32_bits(&mut self, num_bits: u8) -> Result<u32, BitsError> {
        if num_bits > 32 {
            return Err(BitsErrorKind::InvalidInput.into());
        }
        loop {
            match self.used.cmp(&num_bits) {
                Ordering::Less => {
                    // used < numbits - add more.
                    let v = self.delegate.read_u8()?;
                    self.buf = (self.buf << 8) | v as u32;
                    self.used += 8;
                }
                Ordering::Equal => {
                    let mask = (1u32 << num_bits) - 1;
                    self.used = 0;
                    let b = self.buf & mask;
                    self.buf = 0;
                    return Ok(b);
                }
                Ordering::Greater => {
                    let rem = self.used - num_bits;
                    let mask = (1u32 << num_bits) - 1;
                    let b = (self.buf >> rem) & mask;
                    self.used -= num_bits;
                    return Ok(b);
                }
            }
        }
    }
}
#[cfg(all(test, feature = "std"))]
mod test {
    use crate::{BitStreamDecoder, BitStreamEncoder, BitsError, BitsWrapper};

    #[test]
    pub fn test_dec() -> Result<(), BitsError> {
        let buf = vec![0xAB, 0xCD, 0xAB, 0xCD];
        let mut dec = BitStreamDecoder::new(BitsWrapper::Owned(buf));
        assert_eq!(0xA, dec.read_u32_bits(4)?);
        assert_eq!(0xB, dec.read_u32_bits(4)?);
        assert_eq!(0xC, dec.read_u32_bits(4)?);
        assert_eq!(0xD, dec.read_u32_bits(4)?);
        assert_eq!(0xABCD, dec.read_u32_bits(16)?);
        Ok(())
    }

    #[test]
    pub fn test_dec2() -> Result<(), BitsError> {
        let buf = vec![0x03, 0xC0, 0x81, 0x00, 0x88, 0x10, 0x1A, 0x02];
        let mut dec = BitStreamDecoder::new(BitsWrapper::Owned(buf));
        assert_eq!(7, dec.read_u32_bits(9)?);
        assert_eq!(258, dec.read_u32_bits(9)?);
        assert_eq!(8, dec.read_u32_bits(9)?);
        assert_eq!(8, dec.read_u32_bits(9)?);
        assert_eq!(258, dec.read_u32_bits(9)?);
        assert_eq!(6, dec.read_u32_bits(9)?);
        assert_eq!(257, dec.read_u32_bits(9)?);

        Ok(())
    }

    #[test]
    pub fn test_enc() -> Result<(), BitsError> {
        let mut buf = Vec::<u8>::new();
        {
            let wrap = BitsWrapper::Borrowed(&mut buf);
            let mut enc = BitStreamEncoder::new(wrap);

            enc.write_u16_bits(0xAAAA, 4)?;
            enc.write_u16_bits(0xBBBB, 4)?;
            enc.write_u16_bits(0xCCCC, 4)?;
            enc.write_u16_bits(0xDDDD, 4)?;
            enc.write_u16_bits(0xABCD, 16)?;
        }
        // println!("{:?}", buf);
        assert_eq!(buf, [0xAB, 0xCD, 0xAB, 0xCD]);
        Ok(())
    }

    #[test]
    pub fn test_enc2() -> Result<(), BitsError> {
        let mut buf = Vec::<u8>::new();
        {
            let wrap = BitsWrapper::Borrowed(&mut buf);
            let mut enc = BitStreamEncoder::new(wrap);

            enc.write_u16_bits(7, 9)?;
            enc.write_u16_bits(258, 9)?;
            enc.write_u16_bits(8, 9)?;
            enc.write_u16_bits(8, 9)?;
            enc.write_u16_bits(258, 9)?;
            enc.write_u16_bits(6, 9)?;
            enc.write_u16_bits(257, 9)?;
        }
        assert_eq!(buf, [0x03, 0xC0, 0x81, 0x00, 0x88, 0x10, 0x1A, 0x02]);
        // 0x007  0b000000111
        // 0x102             100000010
        // 0x008                      000001000
        // 0x008                               000001000
        // 0x102                                        100000010
        // 0x006                                                 000000011
        // 0x03 = 0b00000011
        // 0xC0 =           11000000
        // 0x81 =                   10000001
        // 0x00 =                           00000000
        // 0x88 =                                   10001000
        // 0x10 =                                           00010000

        Ok(())
    }
}