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1 | //! Bitstream writer functionality. | |
2 | //! | |
3 | //! Bitstream writer works on `Vec<u8>` and allows to write bits in different modes. | |
4 | //! | |
5 | //! # Examples | |
6 | //! | |
7 | //! Writing 17-bit value: | |
8 | //! ``` | |
9 | //! use nihav_core::io::bitwriter::{BitWriter,BitWriterMode}; | |
10 | //! | |
11 | //! # fn foo() -> Vec<u8> { | |
12 | //! let mut bw = BitWriter::new(Vec::new(), BitWriterMode::BE); | |
13 | //! bw.write(42, 17); | |
14 | //! # bw.end() | |
15 | //! # } | |
16 | //! ``` | |
17 | ||
18 | /// Bitstream writing modes. | |
19 | #[derive(Debug,Clone,Copy,PartialEq)] | |
20 | pub enum BitWriterMode { | |
21 | /// The stream is big endian MSB first. | |
22 | BE, | |
23 | /// The stream is little endian LSB first. | |
24 | LE, | |
25 | /// The stream is packed into 16-bit little-endian words MSB first. | |
26 | LE16MSB, | |
27 | /// The stream is packed into 32-bit little-endian words MSB first. | |
28 | LE32MSB, | |
29 | } | |
30 | ||
31 | impl BitWriterMode { | |
32 | fn is_be(self) -> bool { self != BitWriterMode::LE } | |
33 | } | |
34 | ||
35 | /// Bitstream writer. | |
36 | pub struct BitWriter { | |
37 | dst: Vec<u8>, | |
38 | bitbuf: u32, | |
39 | bits: u8, | |
40 | start: usize, | |
41 | mode: BitWriterMode, | |
42 | } | |
43 | ||
44 | impl BitWriter { | |
45 | /// Creates a new instance of `BitWriter` that will append data to the input vector. | |
46 | /// | |
47 | /// # Examples | |
48 | /// | |
49 | /// ``` | |
50 | /// use nihav_core::io::bitwriter::{BitWriter,BitWriterMode}; | |
51 | /// | |
52 | /// let mut bw = BitWriter::new(Vec::with_capacity(100), BitWriterMode::BE); | |
53 | /// ``` | |
54 | pub fn new(dst: Vec<u8>, mode: BitWriterMode) -> Self { | |
55 | let start = dst.len(); | |
56 | Self { | |
57 | dst, | |
58 | mode, | |
59 | start, | |
60 | bitbuf: 0, | |
61 | bits: 0, | |
62 | } | |
63 | } | |
64 | /// Writes single zero bit to the output. | |
65 | pub fn write0(&mut self) { self.write_bit(false); } | |
66 | /// Writes single set bit to the output. | |
67 | pub fn write1(&mut self) { self.write_bit(true); } | |
68 | /// Writes single bit. | |
69 | pub fn write_bit(&mut self, bit: bool) { | |
70 | if self.mode.is_be() { | |
71 | self.bitbuf |= (bit as u32) << (31 - self.bits); | |
72 | } else { | |
73 | self.bitbuf |= (bit as u32) << self.bits; | |
74 | } | |
75 | self.bits += 1; | |
76 | self.flush(); | |
77 | } | |
78 | /// Writes `bits` bits of `val` value to the output. | |
79 | #[allow(clippy::collapsible_if)] | |
80 | #[allow(clippy::collapsible_else_if)] | |
81 | pub fn write(&mut self, val: u32, bits: u8) { | |
82 | if bits == 0 { | |
83 | return; | |
84 | } | |
85 | if self.mode.is_be() { | |
86 | if self.bits + bits <= 32 { | |
87 | self.bitbuf |= val << (32 - self.bits - bits); | |
88 | self.bits += bits; | |
89 | self.flush(); | |
90 | } else { | |
91 | let cbits = 32 - self.bits; | |
92 | let bits2 = bits - cbits; | |
93 | self.write(val >> bits2, cbits); | |
94 | self.write(val & ((1 << bits2) - 1), bits2); | |
95 | } | |
96 | } else { | |
97 | if self.bits + bits <= 32 { | |
98 | self.bitbuf |= val << self.bits; | |
99 | self.bits += bits; | |
100 | self.flush(); | |
101 | } else { | |
102 | let cbits = 32 - self.bits; | |
103 | let bits2 = bits - cbits; | |
104 | self.write(val & ((1 << cbits) - 1), cbits); | |
105 | self.write(val >> cbits, bits2); | |
106 | } | |
107 | } | |
108 | } | |
109 | /// Writes `bits` bits of signed `val` value to the output. | |
110 | pub fn write_s(&mut self, val: i32, bits: u8) { | |
111 | self.write((val as u32) & ((1 << bits) - 1), bits); | |
112 | } | |
113 | /// Tells the amount of bits written so far. | |
114 | pub fn tell(&self) -> usize { | |
115 | (self.dst.len() - self.start) * 8 + (self.bits as usize) | |
116 | } | |
117 | fn flush(&mut self) { | |
118 | match self.mode { | |
119 | BitWriterMode::BE => { | |
120 | while self.bits >= 8 { | |
121 | self.dst.push((self.bitbuf >> 24) as u8); | |
122 | self.bitbuf <<= 8; | |
123 | self.bits -= 8; | |
124 | } | |
125 | }, | |
126 | BitWriterMode::LE => { | |
127 | while self.bits >= 8 { | |
128 | self.dst.push(self.bitbuf as u8); | |
129 | self.bitbuf >>= 8; | |
130 | self.bits -= 8; | |
131 | } | |
132 | }, | |
133 | BitWriterMode::LE16MSB => { | |
134 | while self.bits >= 16 { | |
135 | self.dst.push((self.bitbuf >> 16) as u8); | |
136 | self.dst.push((self.bitbuf >> 24) as u8); | |
137 | self.bitbuf <<= 16; | |
138 | self.bits -= 16; | |
139 | } | |
140 | }, | |
141 | BitWriterMode::LE32MSB => { | |
142 | if self.bits == 32 { | |
143 | self.dst.push( self.bitbuf as u8); | |
144 | self.dst.push((self.bitbuf >> 8) as u8); | |
145 | self.dst.push((self.bitbuf >> 16) as u8); | |
146 | self.dst.push((self.bitbuf >> 24) as u8); | |
147 | self.bitbuf = 0; | |
148 | self.bits = 0; | |
149 | } | |
150 | }, | |
151 | }; | |
152 | } | |
153 | /// Finalises operations and returns the vector containing output data. | |
154 | pub fn end(mut self) -> Vec<u8> { | |
155 | self.flush(); | |
156 | if self.bits > 0 { | |
157 | match self.mode { | |
158 | BitWriterMode::BE => { | |
159 | self.dst.push((self.bitbuf >> 24) as u8); | |
160 | }, | |
161 | BitWriterMode::LE => { | |
162 | self.dst.push(self.bitbuf as u8); | |
163 | }, | |
164 | BitWriterMode::LE16MSB => { | |
165 | self.dst.push((self.bitbuf >> 16) as u8); | |
166 | self.dst.push((self.bitbuf >> 24) as u8); | |
167 | }, | |
168 | BitWriterMode::LE32MSB => { | |
169 | self.dst.push( self.bitbuf as u8); | |
170 | self.dst.push((self.bitbuf >> 8) as u8); | |
171 | self.dst.push((self.bitbuf >> 16) as u8); | |
172 | self.dst.push((self.bitbuf >> 24) as u8); | |
173 | }, | |
174 | }; | |
175 | } | |
176 | self.dst | |
177 | } | |
178 | } | |
179 | ||
180 | #[cfg(test)] | |
181 | mod test { | |
182 | use super::*; | |
183 | ||
184 | #[test] | |
185 | fn bw_works() { | |
186 | let mut bw = BitWriter::new(Vec::new(), BitWriterMode::BE); | |
187 | bw.write(43, 9); | |
188 | let data = bw.end(); | |
189 | assert_eq!(&data, &[21, 128]); | |
190 | ||
191 | let mut bw = BitWriter::new(Vec::new(), BitWriterMode::LE); | |
192 | bw.write1(); | |
193 | bw.write(43, 9); | |
194 | let data = bw.end(); | |
195 | assert_eq!(&data, &[87, 0]); | |
196 | ||
197 | let mut bw = BitWriter::new(Vec::new(), BitWriterMode::LE32MSB); | |
198 | bw.write(42, 9); | |
199 | bw.write(42, 9); | |
200 | let data = bw.end(); | |
201 | assert_eq!(&data, &[0, 128, 10, 21]); | |
202 | } | |
203 | } |