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90aa4e6b KS |
1 | #[derive(Debug)] |
2 | pub enum BitReaderMode { | |
3 | BE, | |
a961f92b KS |
4 | LE, |
5 | LE16MSB, | |
6 | LE32MSB, | |
90aa4e6b KS |
7 | } |
8 | ||
9 | #[derive(Debug)] | |
10 | pub enum BitReaderError { | |
11 | BitstreamEnd, | |
12 | TooManyBitsRequested, | |
a961f92b | 13 | InvalidValue, |
90aa4e6b KS |
14 | } |
15 | ||
16 | use self::BitReaderError::*; | |
17 | ||
a961f92b | 18 | pub type BitReaderResult<T> = Result<T, BitReaderError>; |
90aa4e6b KS |
19 | |
20 | #[derive(Debug)] | |
21 | pub struct BitReader<'a> { | |
22 | cache: u64, | |
23 | bits: u8, | |
24 | pos: usize, | |
25 | end: usize, | |
26 | src: &'a [u8], | |
27 | mode: BitReaderMode, | |
28 | } | |
29 | ||
30 | impl<'a> BitReader<'a> { | |
31 | ||
32 | pub fn new(src: &'a [u8], size: usize, mode: BitReaderMode) -> Self { | |
33 | if src.len() < size { panic!("size is less than needed"); } | |
34 | BitReader{ cache: 0, pos: 0, bits: 0, end: size, src: src, mode: mode } | |
35 | } | |
36 | ||
37 | pub fn tell(&self) -> usize { | |
38 | self.pos * 8 - (self.bits as usize) | |
39 | } | |
40 | ||
41 | pub fn left(&self) -> isize { | |
42 | ((self.end as isize) - (self.pos as isize)) * 8 + (self.bits as isize) | |
43 | } | |
44 | ||
45 | fn fill32be(&mut self, src: &[u8]) { | |
46 | let nw = (((src[0] as u32) << 24) | | |
47 | ((src[1] as u32) << 16) | | |
48 | ((src[2] as u32) << 8) | | |
49 | ((src[3] as u32) << 0)) as u64; | |
50 | self.cache |= nw << (32 - self.bits); | |
51 | } | |
52 | ||
8ab3904c | 53 | fn fill32le16(&mut self, src: &[u8]) { |
dfc5d644 KS |
54 | let nw = (((src[1] as u32) << 24) | |
55 | ((src[0] as u32) << 16) | | |
56 | ((src[3] as u32) << 8) | | |
57 | ((src[2] as u32) << 0)) as u64; | |
8ab3904c | 58 | self.cache |= nw << (32 - self.bits); |
90aa4e6b KS |
59 | } |
60 | ||
8ab3904c | 61 | fn fill32le32(&mut self, src: &[u8], lsb: bool) { |
90aa4e6b KS |
62 | let nw = (((src[3] as u32) << 24) | |
63 | ((src[2] as u32) << 16) | | |
64 | ((src[1] as u32) << 8) | | |
65 | ((src[0] as u32) << 0)) as u64; | |
8ab3904c KS |
66 | if lsb { |
67 | self.cache |= nw << self.bits; | |
68 | } else { | |
69 | self.cache |= nw << (32 - self.bits); | |
70 | } | |
90aa4e6b KS |
71 | } |
72 | ||
83b49341 | 73 | #[inline(always)] |
90aa4e6b KS |
74 | fn refill(&mut self) -> BitReaderResult<()> { |
75 | if self.pos >= self.end { return Err(BitstreamEnd) } | |
76 | while self.bits <= 32 { | |
77 | if self.pos + 4 <= self.end { | |
78 | let buf = &self.src[self.pos..]; | |
79 | match self.mode { | |
a961f92b | 80 | BitReaderMode::BE => self.fill32be (buf), |
8ab3904c KS |
81 | BitReaderMode::LE16MSB => self.fill32le16(buf), |
82 | BitReaderMode::LE => self.fill32le32(buf, true), | |
83 | BitReaderMode::LE32MSB => self.fill32le32(buf, false), | |
90aa4e6b KS |
84 | } |
85 | self.pos += 4; | |
86 | self.bits += 32; | |
87 | } else { | |
88 | let mut buf: [u8; 4] = [0, 0, 0, 0]; | |
89 | let mut newbits: u8 = 0; | |
90 | for i in 0..3 { | |
91 | if self.pos < self.end { | |
92 | buf[i] = self.src[self.pos]; | |
93 | self.pos = self.pos + 1; | |
94 | newbits += 8; | |
95 | } | |
96 | } | |
97 | if newbits == 0 { break; } | |
98 | match self.mode { | |
a961f92b | 99 | BitReaderMode::BE => self.fill32be (&buf), |
8ab3904c KS |
100 | BitReaderMode::LE16MSB => self.fill32le16(&buf), |
101 | BitReaderMode::LE => self.fill32le32(&buf, true), | |
102 | BitReaderMode::LE32MSB => self.fill32le32(&buf, false), | |
90aa4e6b KS |
103 | } |
104 | self.bits += newbits; | |
105 | } | |
106 | } | |
107 | Ok(()) | |
108 | } | |
109 | ||
83b49341 | 110 | #[inline(always)] |
90aa4e6b KS |
111 | fn read_cache(&mut self, nbits: u8) -> u32 { |
112 | let res = match self.mode { | |
a961f92b KS |
113 | BitReaderMode::LE => ((1u64 << nbits) - 1) & self.cache, |
114 | _ => (self.cache as u64) >> (64 - nbits), | |
90aa4e6b KS |
115 | }; |
116 | res as u32 | |
117 | } | |
118 | ||
a961f92b KS |
119 | fn read_cache_s(&mut self, nbits: u8) -> i32 { |
120 | let res = match self.mode { | |
121 | BitReaderMode::LE => ((self.cache as i64) << (64 - nbits)) >> (64 - nbits), | |
122 | _ => (self.cache as i64) >> (64 - nbits), | |
123 | }; | |
124 | res as i32 | |
125 | } | |
126 | ||
83b49341 | 127 | #[inline(always)] |
90aa4e6b KS |
128 | fn skip_cache(&mut self, nbits: u8) { |
129 | match self.mode { | |
a961f92b KS |
130 | BitReaderMode::LE => self.cache >>= nbits, |
131 | _ => self.cache <<= nbits, | |
90aa4e6b KS |
132 | }; |
133 | self.bits -= nbits; | |
134 | } | |
135 | ||
83b49341 | 136 | #[inline(always)] |
90aa4e6b KS |
137 | fn reset_cache(&mut self) { |
138 | self.bits = 0; | |
139 | self.cache = 0; | |
140 | } | |
141 | ||
83b49341 | 142 | #[inline(always)] |
90aa4e6b | 143 | pub fn read(&mut self, nbits: u8) -> BitReaderResult<u32> { |
a961f92b | 144 | if nbits == 0 { return Ok(0) } |
90aa4e6b KS |
145 | if nbits > 32 { return Err(TooManyBitsRequested) } |
146 | if self.bits < nbits { | |
147 | if let Err(err) = self.refill() { return Err(err) } | |
148 | if self.bits < nbits { return Err(BitstreamEnd) } | |
149 | } | |
150 | let res = self.read_cache(nbits); | |
151 | self.skip_cache(nbits); | |
a961f92b KS |
152 | Ok(res) |
153 | } | |
154 | ||
155 | pub fn read_s(&mut self, nbits: u8) -> BitReaderResult<i32> { | |
156 | if nbits == 0 || nbits > 32 { return Err(TooManyBitsRequested) } | |
157 | if self.bits < nbits { | |
158 | if let Err(err) = self.refill() { return Err(err) } | |
159 | if self.bits < nbits { return Err(BitstreamEnd) } | |
160 | } | |
161 | let res = self.read_cache_s(nbits); | |
162 | self.skip_cache(nbits); | |
163 | Ok(res) | |
90aa4e6b KS |
164 | } |
165 | ||
83b49341 | 166 | #[inline(always)] |
0a1d94d9 KS |
167 | pub fn read_bool(&mut self) -> BitReaderResult<bool> { |
168 | if self.bits < 1 { | |
169 | if let Err(err) = self.refill() { return Err(err) } | |
170 | if self.bits < 1 { return Err(BitstreamEnd) } | |
171 | } | |
172 | let res = self.read_cache(1); | |
173 | self.skip_cache(1); | |
174 | Ok(res == 1) | |
175 | } | |
176 | ||
83b49341 | 177 | #[inline(always)] |
90aa4e6b KS |
178 | pub fn peek(&mut self, nbits: u8) -> u32 { |
179 | if nbits > 32 { return 0 } | |
180 | if self.bits < nbits { let _ = self.refill(); } | |
181 | self.read_cache(nbits) | |
182 | } | |
183 | ||
83b49341 | 184 | #[inline(always)] |
90aa4e6b KS |
185 | pub fn skip(&mut self, nbits: u32) -> BitReaderResult<()> { |
186 | if self.bits as u32 >= nbits { | |
187 | self.skip_cache(nbits as u8); | |
188 | return Ok(()); | |
189 | } | |
190 | let mut skip_bits = nbits - (self.bits as u32); | |
191 | self.reset_cache(); | |
192 | self.pos += ((skip_bits / 32) * 4) as usize; | |
193 | skip_bits = skip_bits & 0x1F; | |
194 | self.refill()?; | |
195 | if skip_bits > 0 { | |
196 | self.skip_cache(skip_bits as u8); | |
197 | } | |
198 | Ok(()) | |
199 | } | |
200 | ||
201 | pub fn seek(&mut self, nbits: u32) -> BitReaderResult<()> { | |
202 | if ((nbits + 7) >> 3) as usize > self.end { return Err(TooManyBitsRequested); } | |
203 | self.reset_cache(); | |
204 | self.pos = ((nbits / 32) * 4) as usize; | |
205 | self.skip(nbits & 0x1F) | |
206 | } | |
06fd8c88 KS |
207 | |
208 | pub fn align(&mut self) { | |
209 | let pos = self.bits & 7; | |
210 | if pos != 0 { | |
211 | self.skip_cache(pos); | |
212 | } | |
213 | } | |
214 | } | |
215 | ||
216 | pub fn reverse_bits(inval: u32, len: u8) -> u32 { | |
217 | if len == 0 { return 0; } | |
218 | const REV_TAB: [u8; 16] = [ | |
219 | 0b0000, 0b1000, 0b0100, 0b1100, 0b0010, 0b1010, 0b0110, 0b1110, | |
220 | 0b0001, 0b1001, 0b0101, 0b1101, 0b0011, 0b1011, 0b0111, 0b1111, | |
221 | ]; | |
222 | ||
223 | let mut ret = 0; | |
224 | let mut val = inval; | |
225 | for _ in 0..8 { | |
226 | ret = (ret << 4) | (REV_TAB[(val & 0xF) as usize] as u32); | |
227 | val = val >> 4; | |
228 | } | |
229 | ret >> (32 - len) | |
90aa4e6b KS |
230 | } |
231 | ||
232 | #[cfg(test)] | |
233 | mod test { | |
234 | use super::*; | |
235 | ||
236 | #[test] | |
237 | fn br_works() { | |
238 | const DATA: [u8; 18] = [0b00011011; 18]; | |
239 | let src = &DATA; | |
a961f92b | 240 | let mut br = BitReader::new(src, src.len(), BitReaderMode::LE16MSB); |
90aa4e6b KS |
241 | |
242 | for _ in 0..8 { | |
243 | assert_eq!(br.read(16).unwrap(), 0x1B1B); | |
244 | } | |
a961f92b KS |
245 | const DATA2: [u8; 1] = [ 0b00011011 ]; |
246 | let src = &DATA2; | |
247 | let mut br = BitReader::new(src, src.len(), BitReaderMode::LE); | |
248 | assert_eq!(br.read_s(5).unwrap(), -5); | |
90aa4e6b KS |
249 | } |
250 | } |