makepad_zune_inflate/
utils.rs

1/*
2 * Copyright (c) 2023.
3 *
4 * This software is free software;
5 *
6 * You can redistribute it or modify it under terms of the MIT, Apache License or Zlib license
7 */
8
9use core::cell::Cell;
10
11/// make_decode_table_entry() creates a decode table entry for the given symbol
12/// by combining the static part 'decode_results[sym]' with the dynamic part
13/// 'len', which is the remaining codeword length (the codeword length for main
14/// table entries, or the codeword length minus TABLEBITS for subtable entries).
15///
16/// In all cases, we add 'len' to each of the two low-order bytes to create the
17/// appropriately-formatted decode table entry.  See the definitions of the
18/// *_decode_results[] arrays below, where the entry format is described.
19pub(crate) fn make_decode_table_entry(decode_results: &[u32], sym: usize, len: u32) -> u32 {
20    decode_results[sym] + (len << 8) + len
21}
22
23/// A safe version of src.copy_within that helps me because I tend to always
24/// confuse the arguments
25pub fn fixed_copy_within<const SIZE: usize>(
26    dest: &mut [u8], src_offset: usize, dest_offset: usize
27) {
28    // for debug builds ensure we don't go out of bounds
29    debug_assert!(
30        dest_offset + SIZE <= dest.len(),
31        "[dst]: End position {} out of range for slice of length {}",
32        dest_offset + SIZE,
33        dest.len()
34    );
35
36    dest.copy_within(src_offset..src_offset + SIZE, dest_offset);
37}
38
39#[inline(always)]
40pub fn copy_rep_matches(dest: &mut [u8], offset: usize, dest_offset: usize, length: usize) {
41    // This is a slightly complicated rep match copier that has
42    // no bounds check.
43
44    // The only invariant we need to uphold is dest[dest_offset] should
45    // copy from dest[offset]
46    // i.e in the first iteration, the first entry in the window will point
47    // to dest[offset] and the
48    // last entry will point to dest[dest_offset]
49    // it's easy to prove dest[offset] since we take our slice
50    // from offset.
51    // but proving dest[dest_offset] is trickier
52    // If we were at offset, to get to dest_offset, we could
53    // 1. Get difference between dest_offset and offset
54    // 2. Add that difference to offset.
55    //
56
57    let diff = dest_offset - offset + 1;
58
59    // note
60    for window in Cell::from_mut(&mut dest[offset..dest_offset + length + 2])
61        .as_slice_of_cells()
62        .windows(diff)
63    {
64        window.last().unwrap().set(window[0].get());
65    }
66}
67
68/// Return the minimum of two usizes in a const context
69#[rustfmt::skip]
70pub const fn const_min_usize(a: usize, b: usize) -> usize
71{
72    if a < b { a } else { b }
73}
74
75/// Calculate the adler hash of a piece of data.
76#[inline(never)]
77#[cfg(feature = "zlib")]
78pub fn calc_adler_hash(data: &[u8]) -> u32 {
79    use simd_adler32::Adler32;
80    let mut hasher = Adler32::new();
81
82    hasher.write(data);
83
84    hasher.finish()
85}
makepad_zune_inflate/utils.rs

makepad_zune_inflate/
utils.rs
