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1 | #[derive(Debug)] | |
2 | pub enum BitReaderMode { | |
3 | BE, | |
4 | LE, | |
5 | LE16MSB, | |
6 | LE32MSB, | |
7 | } | |
8 | ||
9 | #[derive(Debug)] | |
10 | pub enum BitReaderError { | |
11 | BitstreamEnd, | |
12 | TooManyBitsRequested, | |
13 | InvalidValue, | |
14 | } | |
15 | ||
16 | use self::BitReaderError::*; | |
17 | ||
18 | pub type BitReaderResult<T> = Result<T, BitReaderError>; | |
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 | #[allow(clippy::identity_op)] | |
31 | impl<'a> BitReader<'a> { | |
32 | ||
33 | pub fn new(src: &'a [u8], size: usize, mode: BitReaderMode) -> Self { | |
34 | if src.len() < size { panic!("size is less than needed"); } | |
35 | BitReader{ cache: 0, pos: 0, bits: 0, end: size, src, mode } | |
36 | } | |
37 | ||
38 | pub fn tell(&self) -> usize { | |
39 | self.pos * 8 - (self.bits as usize) | |
40 | } | |
41 | ||
42 | pub fn left(&self) -> isize { | |
43 | ((self.end as isize) - (self.pos as isize)) * 8 + (self.bits as isize) | |
44 | } | |
45 | ||
46 | fn fill32be(&mut self, src: &[u8]) { | |
47 | let nw = (u32::from(src[0]) << 24) | | |
48 | (u32::from(src[1]) << 16) | | |
49 | (u32::from(src[2]) << 8) | | |
50 | (u32::from(src[3]) << 0); | |
51 | self.cache |= u64::from(nw) << (32 - self.bits); | |
52 | } | |
53 | ||
54 | fn fill32le16(&mut self, src: &[u8]) { | |
55 | let nw = (u32::from(src[1]) << 24) | | |
56 | (u32::from(src[0]) << 16) | | |
57 | (u32::from(src[3]) << 8) | | |
58 | (u32::from(src[2]) << 0); | |
59 | self.cache |= u64::from(nw) << (32 - self.bits); | |
60 | } | |
61 | ||
62 | fn fill32le32(&mut self, src: &[u8], lsb: bool) { | |
63 | let nw = (u32::from(src[3]) << 24) | | |
64 | (u32::from(src[2]) << 16) | | |
65 | (u32::from(src[1]) << 8) | | |
66 | (u32::from(src[0]) << 0); | |
67 | if lsb { | |
68 | self.cache |= u64::from(nw) << self.bits; | |
69 | } else { | |
70 | self.cache |= u64::from(nw) << (32 - self.bits); | |
71 | } | |
72 | } | |
73 | ||
74 | #[inline(always)] | |
75 | fn refill(&mut self) -> BitReaderResult<()> { | |
76 | if self.pos >= self.end { return Err(BitstreamEnd) } | |
77 | while self.bits <= 32 { | |
78 | if self.pos + 4 <= self.end { | |
79 | let buf = &self.src[self.pos..]; | |
80 | match self.mode { | |
81 | BitReaderMode::BE => self.fill32be (buf), | |
82 | BitReaderMode::LE16MSB => self.fill32le16(buf), | |
83 | BitReaderMode::LE => self.fill32le32(buf, true), | |
84 | BitReaderMode::LE32MSB => self.fill32le32(buf, false), | |
85 | } | |
86 | self.pos += 4; | |
87 | self.bits += 32; | |
88 | } else { | |
89 | let mut buf: [u8; 4] = [0, 0, 0, 0]; | |
90 | let mut newbits: u8 = 0; | |
91 | for out in buf.iter_mut().take(3) { | |
92 | if self.pos < self.end { | |
93 | *out = self.src[self.pos]; | |
94 | self.pos += 1; | |
95 | newbits += 8; | |
96 | } | |
97 | } | |
98 | if newbits == 0 { break; } | |
99 | match self.mode { | |
100 | BitReaderMode::BE => self.fill32be (&buf), | |
101 | BitReaderMode::LE16MSB => self.fill32le16(&buf), | |
102 | BitReaderMode::LE => self.fill32le32(&buf, true), | |
103 | BitReaderMode::LE32MSB => self.fill32le32(&buf, false), | |
104 | } | |
105 | self.bits += newbits; | |
106 | } | |
107 | } | |
108 | Ok(()) | |
109 | } | |
110 | ||
111 | #[inline(always)] | |
112 | fn read_cache(&mut self, nbits: u8) -> u32 { | |
113 | let res = match self.mode { | |
114 | BitReaderMode::LE => ((1u64 << nbits) - 1) & self.cache, | |
115 | _ => self.cache >> (64 - nbits), | |
116 | }; | |
117 | res as u32 | |
118 | } | |
119 | ||
120 | fn read_cache_s(&mut self, nbits: u8) -> i32 { | |
121 | let res = match self.mode { | |
122 | BitReaderMode::LE => ((self.cache as i64) << (64 - nbits)) >> (64 - nbits), | |
123 | _ => (self.cache as i64) >> (64 - nbits), | |
124 | }; | |
125 | res as i32 | |
126 | } | |
127 | ||
128 | #[inline(always)] | |
129 | fn skip_cache(&mut self, nbits: u8) { | |
130 | match self.mode { | |
131 | BitReaderMode::LE => self.cache >>= nbits, | |
132 | _ => self.cache <<= nbits, | |
133 | }; | |
134 | self.bits -= nbits; | |
135 | } | |
136 | ||
137 | #[inline(always)] | |
138 | fn reset_cache(&mut self) { | |
139 | self.bits = 0; | |
140 | self.cache = 0; | |
141 | } | |
142 | ||
143 | #[inline(always)] | |
144 | pub fn read(&mut self, nbits: u8) -> BitReaderResult<u32> { | |
145 | if nbits == 0 { return Ok(0) } | |
146 | if nbits > 32 { return Err(TooManyBitsRequested) } | |
147 | if self.bits < nbits { | |
148 | if let Err(err) = self.refill() { return Err(err) } | |
149 | if self.bits < nbits { return Err(BitstreamEnd) } | |
150 | } | |
151 | let res = self.read_cache(nbits); | |
152 | self.skip_cache(nbits); | |
153 | Ok(res) | |
154 | } | |
155 | ||
156 | pub fn read_s(&mut self, nbits: u8) -> BitReaderResult<i32> { | |
157 | if nbits == 0 || nbits > 32 { return Err(TooManyBitsRequested) } | |
158 | if self.bits < nbits { | |
159 | if let Err(err) = self.refill() { return Err(err) } | |
160 | if self.bits < nbits { return Err(BitstreamEnd) } | |
161 | } | |
162 | let res = self.read_cache_s(nbits); | |
163 | self.skip_cache(nbits); | |
164 | Ok(res) | |
165 | } | |
166 | ||
167 | #[inline(always)] | |
168 | pub fn read_bool(&mut self) -> BitReaderResult<bool> { | |
169 | if self.bits < 1 { | |
170 | if let Err(err) = self.refill() { return Err(err) } | |
171 | if self.bits < 1 { return Err(BitstreamEnd) } | |
172 | } | |
173 | let res = self.read_cache(1); | |
174 | self.skip_cache(1); | |
175 | Ok(res == 1) | |
176 | } | |
177 | ||
178 | #[inline(always)] | |
179 | pub fn peek(&mut self, nbits: u8) -> u32 { | |
180 | if nbits > 32 { return 0 } | |
181 | if self.bits < nbits { let _ = self.refill(); } | |
182 | self.read_cache(nbits) | |
183 | } | |
184 | ||
185 | #[inline(always)] | |
186 | pub fn skip(&mut self, nbits: u32) -> BitReaderResult<()> { | |
187 | if u32::from(self.bits) >= nbits { | |
188 | self.skip_cache(nbits as u8); | |
189 | return Ok(()); | |
190 | } | |
191 | let mut skip_bits = nbits - u32::from(self.bits); | |
192 | self.reset_cache(); | |
193 | self.pos += ((skip_bits / 32) * 4) as usize; | |
194 | skip_bits &= 0x1F; | |
195 | self.refill()?; | |
196 | if skip_bits > 0 { | |
197 | self.skip_cache(skip_bits as u8); | |
198 | } | |
199 | Ok(()) | |
200 | } | |
201 | ||
202 | pub fn seek(&mut self, nbits: u32) -> BitReaderResult<()> { | |
203 | if ((nbits + 7) >> 3) as usize > self.end { return Err(TooManyBitsRequested); } | |
204 | self.reset_cache(); | |
205 | self.pos = ((nbits / 32) * 4) as usize; | |
206 | self.skip(nbits & 0x1F) | |
207 | } | |
208 | ||
209 | pub fn align(&mut self) { | |
210 | let pos = self.bits & 7; | |
211 | if pos != 0 { | |
212 | self.skip_cache(pos); | |
213 | } | |
214 | } | |
215 | } | |
216 | ||
217 | pub fn reverse_bits(inval: u32, len: u8) -> u32 { | |
218 | if len == 0 { return 0; } | |
219 | const REV_TAB: [u8; 16] = [ | |
220 | 0b0000, 0b1000, 0b0100, 0b1100, 0b0010, 0b1010, 0b0110, 0b1110, | |
221 | 0b0001, 0b1001, 0b0101, 0b1101, 0b0011, 0b1011, 0b0111, 0b1111, | |
222 | ]; | |
223 | ||
224 | let mut ret = 0; | |
225 | let mut val = inval; | |
226 | for _ in 0..8 { | |
227 | ret = (ret << 4) | u32::from(REV_TAB[(val & 0xF) as usize]); | |
228 | val >>= 4; | |
229 | } | |
230 | ret >> (32 - len) | |
231 | } | |
232 | ||
233 | #[cfg(test)] | |
234 | mod test { | |
235 | use super::*; | |
236 | ||
237 | #[test] | |
238 | fn br_works() { | |
239 | const DATA: [u8; 18] = [0b00011011; 18]; | |
240 | let src = &DATA; | |
241 | let mut br = BitReader::new(src, src.len(), BitReaderMode::LE16MSB); | |
242 | ||
243 | for _ in 0..8 { | |
244 | assert_eq!(br.read(16).unwrap(), 0x1B1B); | |
245 | } | |
246 | const DATA2: [u8; 1] = [ 0b00011011 ]; | |
247 | let src = &DATA2; | |
248 | let mut br = BitReader::new(src, src.len(), BitReaderMode::LE); | |
249 | assert_eq!(br.read_s(5).unwrap(), -5); | |
250 | } | |
251 | } |