+//! Bitstream reader functionality.
+//!
+//! Bitstream reader operates on `&[u8]` and allows to read bits from the slice in different modes.
+//!
+//! # Examples
+//!
+//! Reading 17 bits from a bitstream:
+//! ```
+//! use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+//!
+//! # use nihav_core::io::bitreader::BitReaderResult;
+//! # fn foo() -> BitReaderResult<u32> {
+//! let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+//! let mut br = BitReader::new(&bits, BitReaderMode::BE);
+//! let value = br.read(17)?;
+//! # Ok(value)
+//! # }
+//! ```
+//!
+//! Reading some amount of bits and checking how many bits are left:
+//! ```
+//! use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+//!
+//! # use nihav_core::io::bitreader::BitReaderResult;
+//! # fn foo() -> BitReaderResult<()> {
+//! let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+//! let mut br = BitReader::new(&bits, BitReaderMode::BE);
+//! let num_skip_bits = br.read(3)?;
+//! br.skip(num_skip_bits)?;
+//! println!("Now there are {} bits left to read.", br.left());
+//! # Ok(())
+//! # }
+//! ```
+
+
+
+/// Bitstream reading modes.
#[derive(Debug)]
pub enum BitReaderMode {
+ /// 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,
}
+/// A list specifying general bitstream reading errors.
#[derive(Debug)]
pub enum BitReaderError {
+ /// The reader is at the end of bitstream.
BitstreamEnd,
+ /// The caller tried to read too many bits at once (e.g. 128).
TooManyBitsRequested,
+ /// Some argument is invalid.
InvalidValue,
}
use self::BitReaderError::*;
+/// A specialised `Result` type for bitstream operations.
pub type BitReaderResult<T> = Result<T, BitReaderError>;
+/// Bitstream reader.
#[derive(Debug)]
pub struct BitReader<'a> {
cache: u64,
#[allow(clippy::identity_op)]
impl<'a> BitReader<'a> {
+ /// Constructs a new instance of bitstream reader.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+ ///
+ /// let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+ /// let mut br = BitReader::new(&bits, BitReaderMode::BE);
+ /// ```
pub fn new(src: &'a [u8], mode: BitReaderMode) -> Self {
BitReader{ cache: 0, pos: 0, bits: 0, src, mode }
}
+ /// Reports the current bit position in the bitstream (usually simply the number of bits read so far).
pub fn tell(&self) -> usize {
self.pos * 8 - (self.bits as usize)
}
+ /// Reports the amount of bits left until the end of the bitstream.
pub fn left(&self) -> isize {
((self.src.len() as isize) - (self.pos as isize)) * 8 + (self.bits as isize)
}
self.cache = 0;
}
+ /// Reads the specified amount of bits as an unsigned value.
+ ///
+ /// The amount should fit into 32 bits, if you need more then
+ /// you should read it as several parts. If the amount of bits
+ /// requested to read is larger than the amount of bits left the
+ /// call will return [`BitstreamEnd`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+ ///
+ /// # use nihav_core::io::bitreader::BitReaderResult;
+ /// # fn foo() -> BitReaderResult<u32> {
+ /// let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+ /// let mut br = BitReader::new(&bits, BitReaderMode::BE);
+ /// let value = br.read(17)?;
+ /// # Ok(value)
+ /// # }
+ /// ```
+ ///
+ /// [`BitstreamEnd`]: ./enum.BitReaderError.html#variant.BitstreamEnd
#[inline(always)]
pub fn read(&mut self, nbits: u8) -> BitReaderResult<u32> {
if nbits == 0 { return Ok(0) }
Ok(res)
}
+ /// Reads the specified amount of bits as a signed value.
+ ///
+ /// Beside signedness it behaves the same as [`read`].
+ ///
+ /// [`read`]: #method.read
pub fn read_s(&mut self, nbits: u8) -> BitReaderResult<i32> {
if nbits == 0 || nbits > 32 { return Err(TooManyBitsRequested) }
if self.bits < nbits {
Ok(res)
}
+ /// Reads single bit from the stream and interprets it as a boolean value.
#[inline(always)]
pub fn read_bool(&mut self) -> BitReaderResult<bool> {
if self.bits < 1 {
Ok(res == 1)
}
+ /// Retrieves the next bits from the stream without advancing.
+ ///
+ /// If the bitstream is shorter than the amount of bits requested the result is padded with zeroes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+ ///
+ /// # use nihav_core::io::bitreader::BitReaderResult;
+ /// # fn foo() -> BitReaderResult<u32> {
+ /// let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+ /// let mut br = BitReader::new(&bits, BitReaderMode::BE);
+ /// let peek_value = br.peek(8); // this should return 42
+ /// let value = br.read(8)?; // also 42
+ /// # Ok(value)
+ /// # }
+ /// ```
#[inline(always)]
pub fn peek(&mut self, nbits: u8) -> u32 {
if nbits > 32 { return 0 }
self.read_cache(nbits)
}
+ /// Skips the requested amount of bits.
+ ///
+ /// The amount of bits to skip can be arbitrary large.
+ /// If it skips more bits than there are actually in the stream the call will return [`BitstreamEnd`]
+ ///
+ /// [`read`]: #method.read
+ /// [`BitstreamEnd`]: ./enum.BitReaderError.html#variant.BitstreamEnd
#[inline(always)]
pub fn skip(&mut self, nbits: u32) -> BitReaderResult<()> {
if u32::from(self.bits) >= nbits {
Ok(())
}
+ /// Seeks to the absolute bit position in the stream.
+ /// If the requested position lies after the bitstream end the function returns [`TooManyBitsRequested`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+ ///
+ /// # use nihav_core::io::bitreader::BitReaderResult;
+ /// # fn foo() -> BitReaderResult<u32> {
+ /// let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+ /// let mut br = BitReader::new(&bits, BitReaderMode::BE);
+ /// br.seek(16)?;
+ /// let value = br.read(8)?; // this should return 44
+ /// # Ok(value)
+ /// # }
+ /// ```
+ ///
+ /// [`TooManyBitsRequested`]: ./enum.BitReaderError.html#variant.TooManyBitsRequested
pub fn seek(&mut self, nbits: u32) -> BitReaderResult<()> {
if ((nbits + 7) >> 3) as usize > self.src.len() { return Err(TooManyBitsRequested); }
self.reset_cache();
self.skip(nbits & 0x1F)
}
+ /// Aligns the bit position to the next byte boundary. If already at byte boundary the function does nothing.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use nihav_core::io::bitreader::{BitReader,BitReaderMode};
+ ///
+ /// # use nihav_core::io::bitreader::BitReaderResult;
+ /// # fn foo() -> BitReaderResult<()> {
+ /// let bits: [u8; 4] = [ 42, 43, 44, 45 ];
+ /// let mut br = BitReader::new(&bits, BitReaderMode::BE);
+ /// br.skip(17)?; // now reader is at bit position 17
+ /// br.align(); // now reader is at bit position 24
+ /// br.align(); // now reader is still at bit position 24
+ /// # Ok(())
+ /// # }
+ /// ```
pub fn align(&mut self) {
let pos = self.bits & 7;
if pos != 0 {
}
}
+/// Returns a variable with `len` amount of low bits in reverse order.
+///
+/// # Examples
+/// ```
+/// use nihav_core::io::bitreader::reverse_bits;
+/// reverse_bits(0b010101, 6); // the result should be 0b101010
+/// ```
pub fn reverse_bits(inval: u32, len: u8) -> u32 {
if len == 0 { return 0; }
const REV_TAB: [u8; 16] = [
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