| 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 | } |