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use byteorder::ByteOrder;
use byteorder::LittleEndian;
pub struct BitReaderReversed<'s> {
idx: isize,
source: &'s [u8],
bit_container: u64,
bits_in_container: u8,
}
impl<'s> BitReaderReversed<'s> {
pub fn bits_remaining(&self) -> isize {
self.idx + self.bits_in_container as isize
}
pub fn new(source: &'s [u8]) -> BitReaderReversed<'_> {
BitReaderReversed {
idx: source.len() as isize * 8,
source,
bit_container: 0,
bits_in_container: 0,
}
}
fn refill_container(&mut self) {
let want_to_read = 64 - self.bits_in_container;
let can_read = if want_to_read as isize > self.idx {
self.idx
} else {
want_to_read as isize
};
match can_read {
64 => {
self.bit_container = LittleEndian::read_u64(&self.source[self.byte_idx() - 7..]);
self.bits_in_container += 64;
self.idx -= 64;
}
48..=63 => {
self.bit_container <<= 48;
self.bits_in_container += 48;
self.bit_container |= LittleEndian::read_u48(&self.source[self.byte_idx() - 5..]);
self.idx -= 48;
}
32..=47 => {
self.bit_container <<= 32;
self.bits_in_container += 32;
self.bit_container |=
LittleEndian::read_u32(&self.source[self.byte_idx() - 3..]) as u64;
self.idx -= 32;
}
16..=31 => {
self.bit_container <<= 16;
self.bits_in_container += 16;
self.bit_container |=
LittleEndian::read_u16(&self.source[self.byte_idx() - 1..]) as u64;
self.idx -= 16;
}
8..=15 => {
self.bit_container <<= 8;
self.bits_in_container += 8;
self.bit_container |= self.source[self.byte_idx()] as u64;
self.idx -= 8;
}
_ => panic!("For now panic"),
}
}
fn byte_idx(&self) -> usize {
(self.idx as usize - 1) / 8
}
pub fn get_bits(&mut self, n: usize) -> Result<u64, String> {
if n == 0 {
return Ok(0);
}
if n > 64 {
return Err("Cant serve this request. The reader is limited to 64bit".to_owned());
}
let n = n as isize;
if self.bits_remaining() <= 0 {
self.idx -= n;
return Ok(0);
}
if self.bits_remaining() < n {
let emulated_read_shift = n - self.bits_remaining();
let v = self.get_bits(self.bits_remaining() as usize)?;
assert!(self.idx == 0);
let value = v << emulated_read_shift;
self.idx -= emulated_read_shift;
return Ok(value);
}
if (self.bits_in_container as isize) < n {
while (self.bits_in_container <= 56) && (self.bits_in_container as isize) < n {
self.refill_container();
}
if (self.bits_in_container as isize) < n {
return Err(format!("Cant fullfill read of {} bytes on reversed bitreader even after refill. Would need a bigger container", n));
}
}
let value = self.bit_container >> (self.bits_in_container as isize - n);
self.bits_in_container -= n as u8;
let value_masked = value & ((1 << n) - 1);
assert!(value_masked < (1 << n));
Ok(value_masked)
}
pub fn reset(&mut self, new_source: &'s [u8]) {
self.idx = new_source.len() as isize * 8;
self.source = new_source;
self.bit_container = 0;
self.bits_in_container = 0;
}
}