fdeflate/
lib.rs

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1//! A fast deflate implementation.
2//!
3//! This crate contains an optimized implementation of the deflate algorithm tuned to compress PNG
4//! images. It is compatible with standard zlib, but make a bunch of simplifying assumptions that
5//! drastically improve encoding performance:
6//!
7//! - Exactly one block per deflate stream.
8//! - No distance codes except for run length encoding of zeros.
9//! - A single fixed huffman tree trained on a large corpus of PNG images.
10//! - All huffman codes are 12 bits or less.
11//!
12//! It also contains a fast decompressor that supports arbitrary zlib streams but does especially
13//! well on streams that meet the above assumptions.
14//!
15//! # Inspiration
16//!
17//! The algorithms in this crate take inspiration from multiple sources:
18//! * [fpnge](https://github.com/veluca93/fpnge)
19//! * [zune-inflate](https://github.com/etemesi254/zune-image/tree/main/zune-inflate)
20//! * [RealTime Data Compression blog](https://fastcompression.blogspot.com/2015/10/huffman-revisited-part-4-multi-bytes.html)
21#![forbid(unsafe_code)]
22#![warn(missing_docs)]
23
24mod compress;
25mod decompress;
26mod huffman;
27mod tables;
28
29pub use compress::{compress_to_vec, Compressor, StoredOnlyCompressor};
30pub use decompress::{
31    decompress_to_vec, decompress_to_vec_bounded, BoundedDecompressionError, DecompressionError,
32    Decompressor,
33};
34
35/// Build a length limited huffman tree.
36///
37/// Dynamic programming algorithm from fpnge.
38#[doc(hidden)]
39pub fn compute_code_lengths(
40    freqs: &[u64],
41    min_limit: &[u8],
42    max_limit: &[u8],
43    calculated_nbits: &mut [u8],
44) {
45    debug_assert_eq!(freqs.len(), min_limit.len());
46    debug_assert_eq!(freqs.len(), max_limit.len());
47    debug_assert_eq!(freqs.len(), calculated_nbits.len());
48    let len = freqs.len();
49
50    for i in 0..len {
51        debug_assert!(min_limit[i] >= 1);
52        debug_assert!(min_limit[i] <= max_limit[i]);
53    }
54
55    let precision = *max_limit.iter().max().unwrap();
56    let num_patterns = 1 << precision;
57
58    let mut dynp = vec![u64::MAX; (num_patterns + 1) * (len + 1)];
59    let index = |sym: usize, off: usize| sym * (num_patterns + 1) + off;
60
61    dynp[index(0, 0)] = 0;
62    for sym in 0..len {
63        for bits in min_limit[sym]..=max_limit[sym] {
64            let off_delta = 1 << (precision - bits);
65            for off in 0..=num_patterns.saturating_sub(off_delta) {
66                dynp[index(sym + 1, off + off_delta)] = dynp[index(sym, off)]
67                    .saturating_add(freqs[sym] * u64::from(bits))
68                    .min(dynp[index(sym + 1, off + off_delta)]);
69            }
70        }
71    }
72
73    let mut sym = len;
74    let mut off = num_patterns;
75
76    while sym > 0 {
77        sym -= 1;
78        assert!(off > 0);
79
80        for bits in min_limit[sym]..=max_limit[sym] {
81            let off_delta = 1 << (precision - bits);
82            if off_delta <= off
83                && dynp[index(sym + 1, off)]
84                    == dynp[index(sym, off - off_delta)]
85                        .saturating_add(freqs[sym] * u64::from(bits))
86            {
87                off -= off_delta;
88                calculated_nbits[sym] = bits;
89                break;
90            }
91        }
92    }
93
94    for i in 0..len {
95        debug_assert!(calculated_nbits[i] >= min_limit[i]);
96        debug_assert!(calculated_nbits[i] <= max_limit[i]);
97    }
98}
99
100const fn compute_codes<const NSYMS: usize>(lengths: &[u8; NSYMS]) -> Option<[u16; NSYMS]> {
101    let mut codes = [0u16; NSYMS];
102
103    let mut code = 0u32;
104
105    let mut len = 1;
106    while len <= 16 {
107        let mut i = 0;
108        while i < lengths.len() {
109            if lengths[i] == len {
110                codes[i] = (code as u16).reverse_bits() >> (16 - len);
111                code += 1;
112            }
113            i += 1;
114        }
115        code <<= 1;
116        len += 1;
117    }
118
119    if code == 2 << 16 {
120        Some(codes)
121    } else {
122        None
123    }
124}
fdeflate/lib.rs

fdeflate/
lib.rs
