--- /dev/null
+//! Bitstream writer functionality.
+//!
+//! Bitstream writer works on `Vec<u8>` and allows to write bits in different modes.
+//!
+//! # Examples
+//!
+//! Writing 17-bit value:
+//! ```
+//! use nihav_core::io::bitwriter::{BitWriter,BitWriterMode};
+//!
+//! # fn foo() -> Vec<u8> {
+//! let mut bw = BitWriter::new(Vec::new(), BitWriterMode::BE);
+//! bw.write(42, 17);
+//! # bw.end()
+//! # }
+//! ```
+
+/// Bitstream writing modes.
+#[derive(Debug,Clone,Copy,PartialEq)]
+pub enum BitWriterMode {
+ /// The stream is big endian MSB first.
+ BE,
+ /// The stream is little endian LSB first.
+ LE,
+ /// The stream is packed into 16-bit little-endian words MSB first.
+ LE16MSB,
+ /// The stream is packed into 32-bit little-endian words MSB first.
+ LE32MSB,
+}
+
+impl BitWriterMode {
+ fn is_be(self) -> bool { self != BitWriterMode::LE }
+}
+
+/// Bitstream writer.
+pub struct BitWriter {
+ dst: Vec<u8>,
+ bitbuf: u32,
+ bits: u8,
+ start: usize,
+ mode: BitWriterMode,
+}
+
+impl BitWriter {
+ /// Creates a new instance of `BitWriter` that will append data to the input vector.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use nihav_core::io::bitwriter::{BitWriter,BitWriterMode};
+ ///
+ /// let mut bw = BitWriter::new(Vec::with_capacity(100), BitWriterMode::BE);
+ /// ```
+ pub fn new(dst: Vec<u8>, mode: BitWriterMode) -> Self {
+ let start = dst.len();
+ Self {
+ dst,
+ mode,
+ start,
+ bitbuf: 0,
+ bits: 0,
+ }
+ }
+ /// Writes single zero bit to the output.
+ pub fn write0(&mut self) { self.write_bit(false); }
+ /// Writes single set bit to the output.
+ pub fn write1(&mut self) { self.write_bit(true); }
+ /// Writes single bit.
+ pub fn write_bit(&mut self, bit: bool) {
+ if self.mode.is_be() {
+ self.bitbuf |= (bit as u32) << (31 - self.bits);
+ } else {
+ self.bitbuf |= (bit as u32) << self.bits;
+ }
+ self.bits += 1;
+ self.flush();
+ }
+ /// Writes `bits` bits of `val` value to the output.
+ #[allow(clippy::collapsible_if)]
+ pub fn write(&mut self, val: u32, bits: u8) {
+ if bits == 0 {
+ return;
+ }
+ if self.mode.is_be() {
+ if self.bits + bits <= 32 {
+ self.bitbuf |= val << (32 - self.bits - bits);
+ self.bits += bits;
+ self.flush();
+ } else {
+ let cbits = 32 - self.bits;
+ let bits2 = bits - cbits;
+ self.write(val >> bits2, cbits);
+ self.write(val & ((1 << bits2) - 1), bits2);
+ }
+ } else {
+ if self.bits + bits <= 32 {
+ self.bitbuf |= val << self.bits;
+ self.bits += bits;
+ self.flush();
+ } else {
+ let cbits = 32 - self.bits;
+ let bits2 = bits - cbits;
+ self.write(val & ((1 << cbits) - 1), cbits);
+ self.write(val >> cbits, bits2);
+ }
+ }
+ }
+ /// Writes `bits` bits of signed `val` value to the output.
+ pub fn write_s(&mut self, val: i32, bits: u8) {
+ self.write((val as u32) & ((1 << bits) - 1), bits);
+ }
+ /// Tells the amount of bits written so far.
+ pub fn tell(&self) -> usize {
+ (self.dst.len() - self.start) * 8 + (self.bits as usize)
+ }
+ fn flush(&mut self) {
+ match self.mode {
+ BitWriterMode::BE => {
+ while self.bits >= 8 {
+ self.dst.push((self.bitbuf >> 24) as u8);
+ self.bitbuf <<= 8;
+ self.bits -= 8;
+ }
+ },
+ BitWriterMode::LE => {
+ while self.bits >= 8 {
+ self.dst.push(self.bitbuf as u8);
+ self.bitbuf >>= 8;
+ self.bits -= 8;
+ }
+ },
+ BitWriterMode::LE16MSB => {
+ while self.bits >= 16 {
+ self.dst.push((self.bitbuf >> 16) as u8);
+ self.dst.push((self.bitbuf >> 24) as u8);
+ self.bitbuf <<= 16;
+ self.bits -= 16;
+ }
+ },
+ BitWriterMode::LE32MSB => {
+ if self.bits == 32 {
+ self.dst.push( self.bitbuf as u8);
+ self.dst.push((self.bitbuf >> 8) as u8);
+ self.dst.push((self.bitbuf >> 16) as u8);
+ self.dst.push((self.bitbuf >> 24) as u8);
+ self.bitbuf = 0;
+ self.bits = 0;
+ }
+ },
+ };
+ }
+ /// Finalises operations and returns the vector containing output data.
+ pub fn end(mut self) -> Vec<u8> {
+ self.flush();
+ if self.bits > 0 {
+ match self.mode {
+ BitWriterMode::BE => {
+ self.dst.push((self.bitbuf >> 24) as u8);
+ },
+ BitWriterMode::LE => {
+ self.dst.push(self.bitbuf as u8);
+ },
+ BitWriterMode::LE16MSB => {
+ self.dst.push((self.bitbuf >> 16) as u8);
+ self.dst.push((self.bitbuf >> 24) as u8);
+ },
+ BitWriterMode::LE32MSB => {
+ self.dst.push( self.bitbuf as u8);
+ self.dst.push((self.bitbuf >> 8) as u8);
+ self.dst.push((self.bitbuf >> 16) as u8);
+ self.dst.push((self.bitbuf >> 24) as u8);
+ },
+ };
+ }
+ self.dst
+ }
+}
+
+#[cfg(test)]
+mod test {
+ use super::*;
+
+ #[test]
+ fn bw_works() {
+ let mut bw = BitWriter::new(Vec::new(), BitWriterMode::BE);
+ bw.write(43, 9);
+ let data = bw.end();
+ assert_eq!(&data, &[21, 128]);
+
+ let mut bw = BitWriter::new(Vec::new(), BitWriterMode::LE);
+ bw.write1();
+ bw.write(43, 9);
+ let data = bw.end();
+ assert_eq!(&data, &[87, 0]);
+
+ let mut bw = BitWriter::new(Vec::new(), BitWriterMode::LE32MSB);
+ bw.write(42, 9);
+ bw.write(42, 9);
+ let data = bw.end();
+ assert_eq!(&data, &[0, 128, 10, 21]);
+ }
+}
projects / nihav.git / commitdiff