+//! Codebook support for bitstream reader.
+//!
+//! Codebook is a set of unique bit strings and values assigned to them.
+//! Since there are many ways to define codebook, this implementation employs [`CodebookDescReader`] trait to provide codebook generator with the codes.
+//! Please also pay attention to the codebook creation mode: if bitstream reader reads bits starting from most significant bit first then you should use [`MSB`] mode and [`LSB`] mode otherwise.
+//!
+//! # Examples
+//!
+//! Create a codebook from arrays with codeword descriptions:
+//! ```
+//! use nihav_core::io::codebook::{ShortCodebookDesc, ShortCodebookDescReader, Codebook, CodebookMode};
+//!
+//! let cb_desc: Vec<ShortCodebookDesc> = vec!(
+//! ShortCodebookDesc { code: 0b00, bits: 2 },
+//! ShortCodebookDesc { code: 0, bits: 0 },
+//! ShortCodebookDesc { code: 0b01, bits: 2 },
+//! ShortCodebookDesc { code: 0b1, bits: 1 });
+//! let mut cr = ShortCodebookDescReader::new(cb_desc);
+//! let cb = Codebook::new(&mut cr, CodebookMode::LSB).unwrap();
+//! ```
+//!
+//! Create a codebook using more flexible [`TableCodebookDescReader`] approach.
+//! This will create a codebook for the following set: `1` -> -2, `01` -> -1, `001` -> 0, `0001` -> 1, `00001` -> 2.
+//! ```
+//! use nihav_core::io::codebook::{TableCodebookDescReader, Codebook, CodebookMode};
+//!
+//! fn map_cb_index(index: usize) -> i16 { (index as i16) - 2 }
+//! const CB_BITS: [u8; 5] = [ 1, 2, 3, 4, 5 ];
+//! const CB_CODES: [u8; 5] = [ 1, 1, 1, 1, 1 ];
+//!
+//! let mut tcr = TableCodebookDescReader::new(&CB_CODES, &CB_BITS, map_cb_index);
+//! let cb = Codebook::new(&mut tcr, CodebookMode::MSB).unwrap();
+//! ```
+//!
+//! Read value using a codebook:
+//! ```no_run
+//! use nihav_core::io::bitreader::BitReader;
+//! use nihav_core::io::codebook::{Codebook, CodebookReader, CodebookMode};
+//! # use nihav_core::io::codebook::{ShortCodebookDesc, ShortCodebookDescReader, CodebookDescReader, CodebookResult};
+//!
+//! # fn foo(br: &mut BitReader) -> CodebookResult<()> {
+//! # let mut cr = ShortCodebookDescReader::new(vec![ShortCodebookDesc { code: 0b00, bits: 2 }]);
+//! let cb = Codebook::new(&mut cr, CodebookMode::MSB).unwrap();
+//! let value = br.read_cb(&cb)?;
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! [`MSB`]: ./enum.CodebookMode.html#variant.MSB
+//! [`LSB`]: ./enum.CodebookMode.html#variant.LSB
+//! [`CodebookDescReader`]: ./trait.CodebookDescReader.html
+//! [`TableCodebookDescReader`]: ./struct.TableCodebookDescReader.html
+
use std::collections::HashMap;
use std::cmp::{max, min};
use super::bitreader::BitReader;
+/// A list specifying general codebook operations errors.
#[derive(Debug)]
pub enum CodebookError {
+ /// Codebook description contains errors.
InvalidCodebook,
+ /// Could not allocate memory for codebook.
MemoryError,
+ /// Bitstream contains a sequence not present in codebook.
InvalidCode,
}
+/// Codebook operation modes.
#[derive(Debug, Copy, Clone)]
pub enum CodebookMode {
+ /// Codes in the codebook should be read most significant bit first.
MSB,
+ /// Codes in the codebook should be read least significant bit first.
LSB,
}
-type CodebookResult<T> = Result<T, CodebookError>;
+/// A specialised `Result` type for codebook operations.
+pub type CodebookResult<T> = Result<T, CodebookError>;
+/// Codebook description for `(code bits, code length, code value)` triplet.
+///
+/// This should be used to create a list of codeword definitions for [`FullCodebookDescReader`].
+///
+/// [`FullCodebookDescReader`]: ./struct.FullCodebookDescReader.html
pub struct FullCodebookDesc<S> {
+ /// Codeword bits.
pub code: u32,
+ /// Codeword length.
pub bits: u8,
+ /// Codeword value (symbol).
pub sym: S,
}
+/// Codebook description for `(code bits, code length)` pair with array index being used as codeword value.
+///
+/// This should be used to create a list of codeword definitions for [`ShortCodebookDescReader`].
+///
+/// [`ShortCodebookDescReader`]: ./struct.ShortCodebookDescReader.html
pub struct ShortCodebookDesc {
+ /// Codeword bits.
pub code: u32,
+ /// Codeword length.
pub bits: u8,
}
+/// The interface for providing a list of codeword definitions to the codebook creator.
+///
+/// The structure implementing this trait should be able to provide the total number of defined codewords and their bits and values. [`ShortCodebookDescReader`] or [`TableCodebookDescReader`] are some examples of such implementation.
+/// Codeword definitions with zero length are ignored (those may be used to create sparse codebook definitions though).
+///
+/// [`ShortCodebookDescReader`]: ./struct.ShortCodebookDescReader.html
+/// [`TableCodebookDescReader`]: ./struct.TableCodebookDescReader.html
pub trait CodebookDescReader<S> {
+ /// Returns the codeword length for the provided index.
fn bits(&mut self, idx: usize) -> u8;
+ /// Returns the codeword bits for the provided index.
fn code(&mut self, idx: usize) -> u32;
+ /// Returns the codeword value (aka codeword symbol) for the provided index.
fn sym (&mut self, idx: usize) -> S;
+ /// Returns the total number of defined codewords.
fn len (&mut self) -> usize;
}
+/// The codebook structure for code reading.
#[allow(dead_code)]
pub struct Codebook<S> {
table: Vec<u32>,
lut_bits: u8,
}
+/// Trait allowing bitreader to use codebook for decoding bit sequences.
pub trait CodebookReader<S> {
+ /// Reads the codeword from the bitstream and returns its value (or [`InvalidCode`] on error).
+ ///
+ /// [`InvalidCode`]: ./enum.CodebookError.html#variant.InvalidCode
fn read_cb(&mut self, cb: &Codebook<S>) -> CodebookResult<S>;
}
impl<S: Copy> Codebook<S> {
+ /// Constructs a new `Codebook` instance using provided codebook description and mode.
pub fn new(cb: &mut CodebookDescReader<S>, mode: CodebookMode) -> CodebookResult<Self> {
let mut maxbits = 0;
let mut nnz = 0;
}
}
+/// Codebook description that stores a list of codewords and their values.
pub struct FullCodebookDescReader<S> {
data: Vec<FullCodebookDesc<S>>,
}
impl<S> FullCodebookDescReader<S> {
+ /// Constructs a new `FullCodebookDescReader` instance.
pub fn new(data: Vec<FullCodebookDesc<S>>) -> Self {
FullCodebookDescReader { data }
}
fn len(&mut self) -> usize { self.data.len() }
}
+/// Codebook description that stores a list of codewords and their value is equal to the index.
pub struct ShortCodebookDescReader {
data: Vec<ShortCodebookDesc>,
}
impl ShortCodebookDescReader {
+ /// Constructs a new `ShortCodebookDescReader` instance.
pub fn new(data: Vec<ShortCodebookDesc<>>) -> Self {
ShortCodebookDescReader { data }
}
fn len(&mut self) -> usize { self.data.len() }
}
+/// Flexible codebook description that uses two separate arrays for codeword bits and lengths and a function that maps codeword index into its symbol.
pub struct TableCodebookDescReader<'a, CodeType:'static, IndexType:'static> {
bits: &'a [u8],
codes: &'a [CodeType],
}
impl<'a, CodeType, IndexType> TableCodebookDescReader<'a, CodeType, IndexType> {
+ /// Constructs a new `TableCodebookDescReader` instance.
pub fn new(codes: &'a [CodeType], bits: &'a [u8], idx_map: fn(usize) -> IndexType) -> Self {
Self { bits, codes, idx_map }
}
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