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use crate::constants::BASE64_KEY;
use crate::constants::CLOSE_CODE;
use crate::constants::START_CODE_BITS;
use crate::constants::U16_CODE;
use crate::constants::U8_CODE;
use crate::constants::URI_KEY;
use crate::IntoWideIter;
use std::convert::TryFrom;
use std::convert::TryInto;
#[derive(Debug)]
pub struct DecompressContext<I> {
val: u16,
compressed_data: I,
position: u16,
reset_val: u16,
}
impl<I> DecompressContext<I>
where
I: Iterator<Item = u16>,
{
#[inline]
pub fn new(mut compressed_data: I, bits_per_char: u8) -> Option<Self> {
assert!(usize::from(bits_per_char) <= std::mem::size_of::<u16>() * 8);
let reset_val_pow = bits_per_char - 1;
let reset_val: u16 = 1 << reset_val_pow;
Some(DecompressContext {
val: compressed_data.next()?,
compressed_data,
position: reset_val,
reset_val,
})
}
#[inline]
pub fn read_bit(&mut self) -> Option<bool> {
let res = self.val & self.position;
self.position >>= 1;
if self.position == 0 {
self.position = self.reset_val;
self.val = self.compressed_data.next()?;
}
Some(res != 0)
}
#[inline]
pub fn read_bits(&mut self, n: u8) -> Option<u32> {
let mut res = 0;
let max_power: u32 = 1 << n;
let mut power: u32 = 1;
while power != max_power {
res |= u32::from(self.read_bit()?) * power;
power <<= 1;
}
Some(res)
}
}
#[inline]
pub fn decompress(compressed: impl IntoWideIter) -> Option<Vec<u16>> {
decompress_internal(compressed.into_wide_iter(), 16)
}
#[inline]
pub fn decompress_from_utf16(compressed: &str) -> Option<Vec<u16>> {
decompress_internal(compressed.encode_utf16().map(|c| c - 32), 15)
}
#[inline]
pub fn decompress_from_encoded_uri_component(compressed: &str) -> Option<Vec<u16>> {
let compressed: Option<Vec<u16>> = compressed
.encode_utf16()
.map(|c| {
if c == u16::from(b' ') {
u16::from(b'+')
} else {
c
}
})
.map(u32::from)
.flat_map(|c| {
URI_KEY
.iter()
.position(|k| u8::try_from(c) == Ok(*k))
.map(|n| u16::try_from(n).ok())
})
.collect();
decompress_internal(compressed?.into_iter(), 6)
}
#[inline]
pub fn decompress_from_base64(compressed: &str) -> Option<Vec<u16>> {
let compressed: Option<Vec<u16>> = compressed
.encode_utf16()
.flat_map(|c| {
BASE64_KEY
.iter()
.position(|k| u8::try_from(c) == Ok(*k))
.map(|n| u16::try_from(n).ok())
})
.collect();
decompress_internal(compressed?.into_iter(), 6)
}
#[inline]
pub fn decompress_from_uint8_array(compressed: &[u8]) -> Option<Vec<u16>> {
let compressed_len = compressed.len();
if compressed_len & 1 == 1 {
return None;
}
let buffer: Vec<u16> = compressed
.chunks(2)
.map(|slice| {
u16::from_be_bytes(slice.try_into().unwrap())
})
.collect();
decompress(&buffer)
}
#[inline]
pub fn decompress_internal<I>(compressed: I, bits_per_char: u8) -> Option<Vec<u16>>
where
I: Iterator<Item = u16>,
{
let mut ctx = match DecompressContext::new(compressed, bits_per_char) {
Some(ctx) => ctx,
None => return Some(Vec::new()),
};
let mut dictionary: Vec<Vec<u16>> = Vec::with_capacity(16);
for i in 0_u16..3_u16 {
dictionary.push(vec![i]);
}
let code = u8::try_from(ctx.read_bits(START_CODE_BITS)?).unwrap();
let first_entry = match code {
U8_CODE | U16_CODE => {
let bits_to_read = (code * 8) + 8;
u16::try_from(ctx.read_bits(bits_to_read)?).unwrap()
}
CLOSE_CODE => return Some(Vec::new()),
_ => return None,
};
dictionary.push(vec![first_entry]);
let mut w = vec![first_entry];
let mut result = vec![first_entry];
let mut num_bits: u8 = 3;
let mut enlarge_in: u64 = 4;
let mut entry;
loop {
let mut code = ctx.read_bits(num_bits)?;
match u8::try_from(code) {
Ok(code_u8 @ (U8_CODE | U16_CODE)) => {
let bits_to_read = (code_u8 * 8) + 8;
let bits = u16::try_from(ctx.read_bits(bits_to_read)?).unwrap();
dictionary.push(vec![bits]);
code = u32::try_from(dictionary.len() - 1).ok()?;
enlarge_in -= 1;
}
Ok(CLOSE_CODE) => return Some(result),
_ => {}
}
if enlarge_in == 0 {
enlarge_in = 1 << num_bits;
num_bits += 1;
}
let code_usize = usize::try_from(code).ok()?;
if let Some(entry_value) = dictionary.get(code_usize) {
entry = entry_value.clone();
} else if code_usize == dictionary.len() {
entry = w.clone();
entry.push(*w.first()?);
} else {
return None;
}
result.extend(&entry);
let mut to_be_inserted = w.clone();
to_be_inserted.push(*entry.first()?);
dictionary.push(to_be_inserted);
enlarge_in -= 1;
w = entry;
if enlarge_in == 0 {
enlarge_in = 1 << num_bits;
num_bits += 1;
}
}
}