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|
//! 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)]
#[allow(clippy::collapsible_else_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]);
}
}
|
