| 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 | src: &'a [u8], |
| 26 | mode: BitReaderMode, |
| 27 | } |
| 28 | |
| 29 | #[allow(clippy::identity_op)] |
| 30 | impl<'a> BitReader<'a> { |
| 31 | |
| 32 | pub fn new(src: &'a [u8], mode: BitReaderMode) -> Self { |
| 33 | BitReader{ cache: 0, pos: 0, bits: 0, src, mode } |
| 34 | } |
| 35 | |
| 36 | pub fn tell(&self) -> usize { |
| 37 | self.pos * 8 - (self.bits as usize) |
| 38 | } |
| 39 | |
| 40 | pub fn left(&self) -> isize { |
| 41 | ((self.src.len() as isize) - (self.pos as isize)) * 8 + (self.bits as isize) |
| 42 | } |
| 43 | |
| 44 | fn fill32be(&mut self, src: &[u8]) { |
| 45 | let nw = (u32::from(src[0]) << 24) | |
| 46 | (u32::from(src[1]) << 16) | |
| 47 | (u32::from(src[2]) << 8) | |
| 48 | (u32::from(src[3]) << 0); |
| 49 | self.cache |= u64::from(nw) << (32 - self.bits); |
| 50 | } |
| 51 | |
| 52 | fn fill32le16(&mut self, src: &[u8]) { |
| 53 | let nw = (u32::from(src[1]) << 24) | |
| 54 | (u32::from(src[0]) << 16) | |
| 55 | (u32::from(src[3]) << 8) | |
| 56 | (u32::from(src[2]) << 0); |
| 57 | self.cache |= u64::from(nw) << (32 - self.bits); |
| 58 | } |
| 59 | |
| 60 | fn fill32le32(&mut self, src: &[u8], lsb: bool) { |
| 61 | let nw = (u32::from(src[3]) << 24) | |
| 62 | (u32::from(src[2]) << 16) | |
| 63 | (u32::from(src[1]) << 8) | |
| 64 | (u32::from(src[0]) << 0); |
| 65 | if lsb { |
| 66 | self.cache |= u64::from(nw) << self.bits; |
| 67 | } else { |
| 68 | self.cache |= u64::from(nw) << (32 - self.bits); |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | #[inline(always)] |
| 73 | fn refill(&mut self) -> BitReaderResult<()> { |
| 74 | if self.pos >= self.src.len() { return Err(BitstreamEnd) } |
| 75 | while self.bits <= 32 { |
| 76 | if self.pos + 4 <= self.src.len() { |
| 77 | let buf = &self.src[self.pos..]; |
| 78 | match self.mode { |
| 79 | BitReaderMode::BE => self.fill32be (buf), |
| 80 | BitReaderMode::LE16MSB => self.fill32le16(buf), |
| 81 | BitReaderMode::LE => self.fill32le32(buf, true), |
| 82 | BitReaderMode::LE32MSB => self.fill32le32(buf, false), |
| 83 | } |
| 84 | self.pos += 4; |
| 85 | self.bits += 32; |
| 86 | } else { |
| 87 | let mut buf: [u8; 4] = [0, 0, 0, 0]; |
| 88 | let mut newbits: u8 = 0; |
| 89 | for out in buf.iter_mut().take(3) { |
| 90 | if self.pos < self.src.len() { |
| 91 | *out = self.src[self.pos]; |
| 92 | self.pos += 1; |
| 93 | newbits += 8; |
| 94 | } |
| 95 | } |
| 96 | if newbits == 0 { break; } |
| 97 | match self.mode { |
| 98 | BitReaderMode::BE => self.fill32be (&buf), |
| 99 | BitReaderMode::LE16MSB => self.fill32le16(&buf), |
| 100 | BitReaderMode::LE => self.fill32le32(&buf, true), |
| 101 | BitReaderMode::LE32MSB => self.fill32le32(&buf, false), |
| 102 | } |
| 103 | self.bits += newbits; |
| 104 | } |
| 105 | } |
| 106 | Ok(()) |
| 107 | } |
| 108 | |
| 109 | #[inline(always)] |
| 110 | fn read_cache(&mut self, nbits: u8) -> u32 { |
| 111 | let res = match self.mode { |
| 112 | BitReaderMode::LE => ((1u64 << nbits) - 1) & self.cache, |
| 113 | _ => self.cache >> (64 - nbits), |
| 114 | }; |
| 115 | res as u32 |
| 116 | } |
| 117 | |
| 118 | fn read_cache_s(&mut self, nbits: u8) -> i32 { |
| 119 | let res = match self.mode { |
| 120 | BitReaderMode::LE => ((self.cache as i64) << (64 - nbits)) >> (64 - nbits), |
| 121 | _ => (self.cache as i64) >> (64 - nbits), |
| 122 | }; |
| 123 | res as i32 |
| 124 | } |
| 125 | |
| 126 | #[inline(always)] |
| 127 | fn skip_cache(&mut self, nbits: u8) { |
| 128 | match self.mode { |
| 129 | BitReaderMode::LE => self.cache >>= nbits, |
| 130 | _ => self.cache <<= nbits, |
| 131 | }; |
| 132 | self.bits -= nbits; |
| 133 | } |
| 134 | |
| 135 | #[inline(always)] |
| 136 | fn reset_cache(&mut self) { |
| 137 | self.bits = 0; |
| 138 | self.cache = 0; |
| 139 | } |
| 140 | |
| 141 | #[inline(always)] |
| 142 | pub fn read(&mut self, nbits: u8) -> BitReaderResult<u32> { |
| 143 | if nbits == 0 { return Ok(0) } |
| 144 | if nbits > 32 { return Err(TooManyBitsRequested) } |
| 145 | if self.bits < nbits { |
| 146 | if let Err(err) = self.refill() { return Err(err) } |
| 147 | if self.bits < nbits { return Err(BitstreamEnd) } |
| 148 | } |
| 149 | let res = self.read_cache(nbits); |
| 150 | self.skip_cache(nbits); |
| 151 | Ok(res) |
| 152 | } |
| 153 | |
| 154 | pub fn read_s(&mut self, nbits: u8) -> BitReaderResult<i32> { |
| 155 | if nbits == 0 || nbits > 32 { return Err(TooManyBitsRequested) } |
| 156 | if self.bits < nbits { |
| 157 | if let Err(err) = self.refill() { return Err(err) } |
| 158 | if self.bits < nbits { return Err(BitstreamEnd) } |
| 159 | } |
| 160 | let res = self.read_cache_s(nbits); |
| 161 | self.skip_cache(nbits); |
| 162 | Ok(res) |
| 163 | } |
| 164 | |
| 165 | #[inline(always)] |
| 166 | pub fn read_bool(&mut self) -> BitReaderResult<bool> { |
| 167 | if self.bits < 1 { |
| 168 | if let Err(err) = self.refill() { return Err(err) } |
| 169 | if self.bits < 1 { return Err(BitstreamEnd) } |
| 170 | } |
| 171 | let res = self.read_cache(1); |
| 172 | self.skip_cache(1); |
| 173 | Ok(res == 1) |
| 174 | } |
| 175 | |
| 176 | #[inline(always)] |
| 177 | pub fn peek(&mut self, nbits: u8) -> u32 { |
| 178 | if nbits > 32 { return 0 } |
| 179 | if self.bits < nbits { let _ = self.refill(); } |
| 180 | self.read_cache(nbits) |
| 181 | } |
| 182 | |
| 183 | #[inline(always)] |
| 184 | pub fn skip(&mut self, nbits: u32) -> BitReaderResult<()> { |
| 185 | if u32::from(self.bits) >= nbits { |
| 186 | self.skip_cache(nbits as u8); |
| 187 | return Ok(()); |
| 188 | } |
| 189 | let mut skip_bits = nbits - u32::from(self.bits); |
| 190 | self.reset_cache(); |
| 191 | self.pos += ((skip_bits / 32) * 4) as usize; |
| 192 | skip_bits &= 0x1F; |
| 193 | self.refill()?; |
| 194 | if skip_bits > 0 { |
| 195 | self.skip_cache(skip_bits as u8); |
| 196 | } |
| 197 | Ok(()) |
| 198 | } |
| 199 | |
| 200 | pub fn seek(&mut self, nbits: u32) -> BitReaderResult<()> { |
| 201 | if ((nbits + 7) >> 3) as usize > self.src.len() { return Err(TooManyBitsRequested); } |
| 202 | self.reset_cache(); |
| 203 | self.pos = ((nbits / 32) * 4) as usize; |
| 204 | self.skip(nbits & 0x1F) |
| 205 | } |
| 206 | |
| 207 | pub fn align(&mut self) { |
| 208 | let pos = self.bits & 7; |
| 209 | if pos != 0 { |
| 210 | self.skip_cache(pos); |
| 211 | } |
| 212 | } |
| 213 | } |
| 214 | |
| 215 | pub fn reverse_bits(inval: u32, len: u8) -> u32 { |
| 216 | if len == 0 { return 0; } |
| 217 | const REV_TAB: [u8; 16] = [ |
| 218 | 0b0000, 0b1000, 0b0100, 0b1100, 0b0010, 0b1010, 0b0110, 0b1110, |
| 219 | 0b0001, 0b1001, 0b0101, 0b1101, 0b0011, 0b1011, 0b0111, 0b1111, |
| 220 | ]; |
| 221 | |
| 222 | let mut ret = 0; |
| 223 | let mut val = inval; |
| 224 | for _ in 0..8 { |
| 225 | ret = (ret << 4) | u32::from(REV_TAB[(val & 0xF) as usize]); |
| 226 | val >>= 4; |
| 227 | } |
| 228 | ret >> (32 - len) |
| 229 | } |
| 230 | |
| 231 | #[cfg(test)] |
| 232 | mod test { |
| 233 | use super::*; |
| 234 | |
| 235 | #[test] |
| 236 | fn br_works() { |
| 237 | const DATA: [u8; 18] = [0b00011011; 18]; |
| 238 | let src = &DATA; |
| 239 | let mut br = BitReader::new(src, BitReaderMode::LE16MSB); |
| 240 | |
| 241 | for _ in 0..8 { |
| 242 | assert_eq!(br.read(16).unwrap(), 0x1B1B); |
| 243 | } |
| 244 | const DATA2: [u8; 1] = [ 0b00011011 ]; |
| 245 | let src = &DATA2; |
| 246 | let mut br = BitReader::new(src, BitReaderMode::LE); |
| 247 | assert_eq!(br.read_s(5).unwrap(), -5); |
| 248 | } |
| 249 | } |