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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
use crate::bit_reader::BitReader;
use crate::error::Error;
use crate::util::CeilLog2;
#[derive(Debug)]
pub struct HybridUint {
split_token: u32,
split_exponent: u32,
msb_in_token: u32,
lsb_in_token: u32,
}
impl HybridUint {
pub(super) fn is_split_exponent_zero(&self) -> bool {
self.split_exponent == 0
}
pub fn decode(log_alpha_size: usize, br: &mut BitReader) -> Result<HybridUint, Error> {
let split_exponent = br.read((log_alpha_size + 1).ceil_log2())? as u32;
let split_token = 1u32 << split_exponent;
let msb_in_token;
let lsb_in_token;
if split_exponent != log_alpha_size as u32 {
let nbits = (split_exponent + 1).ceil_log2() as usize;
msb_in_token = br.read(nbits)? as u32;
if msb_in_token > split_exponent {
return Err(Error::InvalidUintConfig(split_exponent, msb_in_token, None));
}
let nbits = (split_exponent - msb_in_token + 1).ceil_log2() as usize;
lsb_in_token = br.read(nbits)? as u32;
} else {
msb_in_token = 0;
lsb_in_token = 0;
}
if lsb_in_token + msb_in_token > split_exponent {
return Err(Error::InvalidUintConfig(
split_exponent,
msb_in_token,
Some(lsb_in_token),
));
}
Ok(HybridUint {
split_token,
split_exponent,
msb_in_token,
lsb_in_token,
})
}
#[inline]
pub fn read(&self, symbol: u32, br: &mut BitReader) -> u32 {
if symbol < self.split_token {
return symbol;
}
let bits_in_token = self.lsb_in_token + self.msb_in_token;
let nbits =
self.split_exponent - bits_in_token + ((symbol - self.split_token) >> bits_in_token);
// The bitstream is invalid if nbits >= 32. We do not report errors, and just pretend we
// decoded a number <32.
let nbits = nbits & 31;
let low = symbol & ((1 << self.lsb_in_token) - 1);
let symbol_nolow = symbol >> self.lsb_in_token;
let bits = br.read_optimistic(nbits as usize) as u32;
let hi = (symbol_nolow & ((1 << self.msb_in_token) - 1)) | (1 << self.msb_in_token);
(((hi << nbits) | bits) << self.lsb_in_token) | low
}
}
#[cfg(test)]
impl HybridUint {
pub fn new(split_exponent: u32, msb_in_token: u32, lsb_in_token: u32) -> Self {
Self {
split_token: 1 << split_exponent,
split_exponent,
msb_in_token,
lsb_in_token,
}
}
}
#[cfg(test)]
mod test {
#[test]
fn test_hybrid_uint_decode_invalid() {
use super::*;
let mut br = BitReader::new(&[10, 75, 10, 75, 168, 139, 132, 255, 244]);
br.skip_bits(1).unwrap();
if let Ok(uint) = HybridUint::decode(15, &mut br) {
uint.read(1022, &mut br);
}
}
}