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pub const MAX_HUFFMAN_BITS: u16 = 15;
const LUT_SIZE: usize = 2_i32.pow(MAX_HUFFMAN_BITS as u32) as usize;
#[derive(PartialEq, Default)]
pub struct HuffmanTree {
// lut: HashMap<u16, HuffmanCode, BuildHasherDefault<NoHashHasher<u16>>>,
lut: Vec<Option<HuffmanCode>>,
}
#[derive(Copy, Clone, PartialEq, Debug)]
pub struct HuffmanCode {
pub symbol: u16,
pub len: u8,
}
impl HuffmanTree {
pub fn new(bit_lengths: &[u8]) -> Self {
// Count the number of codes for each code length. Let
// bl_count[N] be the number of codes of length N, N >= 1.
// note: bl_count[0] must be 0.
let mut bl_count = [0_u16; (MAX_HUFFMAN_BITS + 1) as usize];
for &len in bit_lengths {
let len = len as usize;
bl_count[len] += 1;
}
bl_count[0] = 0;
// 2) Find the numerical value of the smallest code for each
// code length:
let mut next_code = [0_u16; (MAX_HUFFMAN_BITS + 1) as usize];
let mut code: u16 = 0;
for bits in 1..=MAX_HUFFMAN_BITS {
let bits = bits as usize;
code = (code + bl_count[bits - 1]) << 1;
next_code[bits] = code;
}
// Assign numerical values to all codes.
let mut final_codes = vec![0_u16; bit_lengths.len()];
for (i, &len) in bit_lengths.iter().enumerate() {
if len != 0 {
let len = len as usize;
let code = next_code[len];
next_code[len] += 1;
final_codes[i] = code;
} else {
final_codes[i] = 0;
}
}
// put them in the lookup table.
let mut lut = vec![None; LUT_SIZE];
for i in 0..bit_lengths.len() {
let len = bit_lengths[i];
let code = final_codes[i] as usize;
let i = i as u16;
if len > 0 {
lut[code] = Some(HuffmanCode { symbol: i, len });
}
}
Self { lut }
}
pub fn fixed() -> Self {
let mut test_values: Vec<u8> = vec![];
for (next, bit_len) in [(143, 8), (255, 9), (279, 7), (287, 8)] {
test_values.resize(next + 1, bit_len);
}
Self::new(&test_values)
}
pub fn fixed_dist() -> Self {
let test_values_dist: Vec<u8> = vec![5; 31];
Self::new(&test_values_dist)
}
pub fn decode(&self, code: u16, len: u8) -> Option<u16> {
let code = code as usize;
let lookup = self.lut[code]?;
if len == lookup.len {
Some(lookup.symbol)
} else {
None
}
}
#[cfg(test)]
pub fn get_lut(&self) -> &Vec<Option<HuffmanCode>> {
return &self.lut;
}
pub fn export(&self) {}
}
/**
* TESTS
*/
#[cfg(test)]
mod test {
use crate::huffman::HuffmanCode;
use rstest::*;
use super::HuffmanTree;
#[rstest]
pub fn test_lut_values_correct() {
let test_values: [u8; 8] = [3, 3, 3, 3, 3, 2, 4, 4];
let tree = HuffmanTree::new(&test_values);
let codes = tree.get_lut();
/*
Symbol Length Code
------ ------ ----
0 3 010
1 3 011
2 3 100
3 3 101
4 3 110
5 2 00
6 4 1110
7 4 1111
*/
assert_eq!(codes[0b01], None);
assert_eq!(codes[0b010], Some(HuffmanCode { symbol: 0, len: 3 }));
assert_eq!(codes[0b1111], Some(HuffmanCode { symbol: 7, len: 4 }));
assert_eq!(codes[0b00], Some(HuffmanCode { symbol: 5, len: 2 }));
}
#[rstest]
pub fn test_lut_values_with_gaps() {
let test_values: [u8; 12] = [0, 3, 3, 3, 0, 3, 3, 2, 0, 4, 4, 0];
/*
Symbol Length Code
------ ------ ----
0 N/A
1 3 010
2 3 011
3 3 100
4 N/A
5 3 101
6 3 110
7 2 00
8 N/A
9 4 1110
10 4 1111
11 N/A
*/
let tree = HuffmanTree::new(&test_values);
let codes = tree.get_lut();
assert_eq!(codes[0b01], None);
assert_eq!(codes[0b010], Some(HuffmanCode { symbol: 1, len: 3 }));
assert_eq!(codes[0b1111], Some(HuffmanCode { symbol: 10, len: 4 }));
assert_eq!(codes[0b00], Some(HuffmanCode { symbol: 7, len: 2 }));
}
#[rstest]
pub fn test_lut_values_with_gaps_2() {
//
// Symbol Len Code
// 0 11 11111111100
// 1 12 111111111110
// 2 11 11111111101
// 3 12 111111111111
// 4 N/A
// 5 11 11111111110
// 6 9 111111110
// 7 8 11111110
// 8 7 1111100
// 9 7 1111101
// 10 7 1111110
// 11 6 111010
// 12 6 111011
// 13 6 111100
// 14 5 11010
// 15 5 11011
// 16 4 0010
// 17 5 11100
// 18 4 0011
// 19 4 0100
// 20 4 0101
// 21 4 0110
// 22 3 000
// 23 4 0111
// 24 4 1000
// 25 4 1001
// 26 4 1010
// 27 4 1011
// 28 4 1100
// 29 6 111101
let test_values = [
11_u8, 12, 11, 12, 0, 11, 9, 8, 7, 7, 7, 6, 6, 6, 5, 5, 4, 5, 4, 4, 4, 4, 3, 4, 4, 4,
4, 4, 4, 6, 0, 0, 0, 0, 0, 0, 0, 0,
];
let tree = HuffmanTree::new(&test_values);
let codes = tree.get_lut();
assert_eq!(codes[0b1011], Some(HuffmanCode { symbol: 27, len: 4 }));
assert_eq!(
codes[0b11111111110],
Some(HuffmanCode { symbol: 5, len: 11 })
);
}
#[rstest]
pub fn test_lut_fixed() {
let tree = HuffmanTree::fixed();
let codes = tree.get_lut();
/*
Lit Value Bits Codes
--------- ---- -----
0 - 143 8 00110000 through
10111111
144 - 255 9 110010000 through
111111111
256 - 279 7 0000000 through
0010111
280 - 287 8 11000000 through
11000111
*/
assert_eq!(codes[0b110001], Some(HuffmanCode { symbol: 1, len: 8 }));
assert_eq!(
codes[0b11000111],
Some(HuffmanCode {
symbol: 287,
len: 8
})
);
assert_eq!(
codes[0b111111110],
Some(HuffmanCode {
symbol: 254,
len: 9
})
);
assert_eq!(
codes[0b0000000],
Some(HuffmanCode {
symbol: 256,
len: 7
})
);
assert_eq!(codes[0b1111111111], None);
}
#[rstest]
pub fn test_decode() {
let test_values: [u8; 8] = [3, 3, 3, 3, 3, 2, 4, 4];
let tree = HuffmanTree::new(&test_values);
assert_eq!(tree.decode(0b0, 1), None);
assert_eq!(tree.decode(0b10, 2), None);
assert_eq!(tree.decode(0b010, 3), Some(0));
}
}