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//! Some universal integer codes support for bitstream reader.
use crate::io::bitreader::{BitReader, BitReaderError, BitReaderResult};
/// Unsigned integer code types.
#[derive(Debug)]
pub enum UintCodeType {
/// Code where number is represented as run of ones with terminating zero.
UnaryOnes,
/// Code where number is represented as run of zeroes with terminating one.
UnaryZeroes,
/// Code for 0, 1 and 2 coded as `0`, `10` and `11`
Unary012,
/// Code for 0, 1 and 2 coded as `11`, `10` and `0`
Unary210,
/// General limited unary code with defined run and terminating bit.
LimitedUnary(u32, u32),
/// Limited run of zeroes with terminating one (unless the code has maximum length).
///
/// [`Unary012`] is essentially an alias for `LimitedZeroes(2)`.
///
/// [`Unary012`]: #variant.Unary012
LimitedZeroes(u32),
/// Limited run of one with terminating zero (unless the code has maximum length).
LimitedOnes(u32),
/// Golomb code.
Golomb(u8),
/// Rice code.
Rice(u8),
/// Elias Gamma code (interleaved).
Gamma,
/// Elias Gamma' code (sometimes incorrectly called exp-Golomb).
GammaP,
}
/// Signed integer code types.
pub enum IntCodeType {
/// Golomb code. Last bit represents the sign.
Golomb(u8),
/// Golomb code. Last bit represents the sign.
Rice(u8),
/// Elias Gamma code. Unsigned values are remapped as 0, 1, -1, 2, -2, ...
Gamma,
/// Elias Gamma' code. Unsigned values are remapped as 0, 1, -1, 2, -2, ...
GammaP,
}
/// Universal integer code reader trait for bitstream reader.
///
/// # Examples
///
/// Read an unsigned Golomb code:
/// ````
/// use nihav_core::io::bitreader::*;
/// use nihav_core::io::intcode::{IntCodeReader,UintCodeType};
///
/// # fn foo() -> BitReaderResult<()> {
/// let mem: [u8; 4] = [ 0, 1, 2, 3];
/// let mut br = BitReader::new(&mem, BitReaderMode::BE);
/// let val = br.read_code(UintCodeType::Golomb(3))?;
/// # Ok(())
/// # }
/// ````
///
/// Read signed Elias code:
/// ````
/// use nihav_core::io::bitreader::*;
/// use nihav_core::io::intcode::{IntCodeReader,IntCodeType};
///
/// # fn foo() -> BitReaderResult<()> {
/// let mem: [u8; 4] = [ 0, 1, 2, 3];
/// let mut br = BitReader::new(&mem, BitReaderMode::BE);
/// let val = br.read_code_signed(IntCodeType::Gamma)?;
/// # Ok(())
/// # }
/// ````
pub trait IntCodeReader {
/// Reads an unsigned integer code of requested type.
fn read_code(&mut self, t: UintCodeType) -> BitReaderResult<u32>;
/// Reads signed integer code of requested type.
fn read_code_signed(&mut self, t: IntCodeType) -> BitReaderResult<i32>;
}
fn read_unary(br: &mut BitReader, terminator: u32) -> BitReaderResult<u32> {
let mut res: u32 = 0;
loop {
if br.read(1)? == terminator { return Ok(res); }
res += 1;
}
}
fn read_unary_lim(br: &mut BitReader, len: u32, terminator: u32) -> BitReaderResult<u32> {
let mut res: u32 = 0;
loop {
if br.read(1)? == terminator { return Ok(res); }
res += 1;
if res == len { return Ok(res); }
}
}
fn read_unary210(br: &mut BitReader) -> BitReaderResult<u32> {
let val = read_unary_lim(br, 2, 0)?;
Ok(2 - val)
}
fn read_golomb(br: &mut BitReader, m: u8) -> BitReaderResult<u32> {
if m == 0 { return Err(BitReaderError::InvalidValue); }
let nbits = (8 - m.leading_zeros()) as u8;
if (m & (m - 1)) == 0 { return read_rice(br, nbits); }
let cutoff = u32::from((1 << nbits) - m);
let pfx = read_unary(br, 0)?;
let tail = br.read(nbits - 1)?;
if tail < cutoff {
let res = pfx * u32::from(m) + tail;
Ok (res)
} else {
let add = br.read(1)?;
let res = pfx * u32::from(m) + (tail - cutoff) * 2 + add + cutoff;
Ok (res)
}
}
fn read_rice(br: &mut BitReader, k: u8) -> BitReaderResult<u32> {
let pfx = read_unary(br, 1)?;
let ret = (pfx << k) + br.read(k)?;
Ok(ret)
}
fn read_gamma(br: &mut BitReader) -> BitReaderResult<u32> {
let mut ret = 1;
while br.read(1)? != 1 {
ret = (ret << 1) | br.read(1)?;
}
Ok(ret - 1)
}
fn read_gammap(br: &mut BitReader) -> BitReaderResult<u32> {
let pfx = read_unary(br, 1)?;
if pfx > 32 { return Err(BitReaderError::InvalidValue); }
let ret = (1 << pfx) + br.read(pfx as u8)?;
Ok(ret)
}
fn uval_to_sval0mp(uval: u32) -> i32 {
if (uval & 1) != 0 { -((uval >> 1) as i32) }
else { (uval >> 1) as i32 }
}
fn uval_to_sval0pm(uval: u32) -> i32 {
if (uval & 1) != 0 { ((uval + 1) >> 1) as i32 }
else { -((uval >> 1) as i32) }
}
impl<'a> IntCodeReader for BitReader<'a> {
#[inline(always)]
fn read_code(&mut self, t: UintCodeType) -> BitReaderResult<u32> {
match t {
UintCodeType::UnaryOnes => read_unary(self, 0),
UintCodeType::UnaryZeroes => read_unary(self, 1),
UintCodeType::LimitedZeroes(len) => read_unary_lim(self, len, 1),
UintCodeType::LimitedOnes(len) => read_unary_lim(self, len, 0),
UintCodeType::LimitedUnary(len, term) => read_unary_lim(self, len, term),
UintCodeType::Unary012 => read_unary_lim(self, 2, 0),
UintCodeType::Unary210 => read_unary210(self),
UintCodeType::Golomb(m) => read_golomb(self, m),
UintCodeType::Rice(k) => read_rice(self, k),
UintCodeType::Gamma => read_gamma(self),
UintCodeType::GammaP => read_gammap(self),
}
}
#[allow(unused_variables)]
fn read_code_signed(&mut self, t: IntCodeType) -> BitReaderResult<i32> {
let uval =
match t {
IntCodeType::Golomb(m) => read_golomb(self, m)?,
IntCodeType::Rice(k) => read_rice(self, k)?,
IntCodeType::Gamma => read_gamma(self)?,
IntCodeType::GammaP => read_gammap(self)?,
};
match t {
IntCodeType::Golomb(m) => Ok(uval_to_sval0mp(uval)),
IntCodeType::Rice(k) => Ok(uval_to_sval0mp(uval)),
IntCodeType::Gamma => Ok(uval_to_sval0pm(uval)),
IntCodeType::GammaP => Ok(uval_to_sval0pm(uval)),
}
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::io::bitreader::*;
#[test]
fn int_codes() {
const GDATA: [u8; 6] = [0b000_001_01, 0b0_0110_011, 0b1_1000_100, 0b1_1010_101, 0b10_10111_1, 0b1000_0000];
let src = &GDATA;
let mut br = BitReader::new(src, BitReaderMode::BE);
for i in 0..11 {
assert_eq!(br.read_code(UintCodeType::Golomb(5)).unwrap(), i);
}
}
}
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