zenzop 0.4.1

A faster fork of the Zopfli DEFLATE compressor with optional ECT-derived optimizations.
Documentation 
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const LENGTH_SYMBOL_TABLE: [usize; 288 /* Originally, 259 entries */] = [
    0, 0, 0, 257, 258, 259, 260, 261, 262, 263, 264, 265, 265, 266, 266, 267, 267, 268, 268, 269,
    269, 269, 269, 270, 270, 270, 270, 271, 271, 271, 271, 272, 272, 272, 272, 273, 273, 273, 273,
    273, 273, 273, 273, 274, 274, 274, 274, 274, 274, 274, 274, 275, 275, 275, 275, 275, 275, 275,
    275, 276, 276, 276, 276, 276, 276, 276, 276, 277, 277, 277, 277, 277, 277, 277, 277, 277, 277,
    277, 277, 277, 277, 277, 277, 278, 278, 278, 278, 278, 278, 278, 278, 278, 278, 278, 278, 278,
    278, 278, 278, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279, 279,
    280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 280, 281, 281, 281,
    281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 281,
    281, 281, 281, 281, 281, 281, 281, 281, 281, 281, 282, 282, 282, 282, 282, 282, 282, 282, 282,
    282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282, 282,
    282, 282, 282, 282, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283,
    283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 283, 284, 284,
    284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 284,
    284, 284, 284, 284, 284, 284, 284, 284, 284, 284, 285,
    // Padding to 288 entries for reduced bounds checking
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
];

/// Gets the symbol for the given length, cfr. the DEFLATE spec.
/// Returns symbol in range [257-285] (inclusive).
pub const fn get_length_symbol(length: usize) -> usize {
    LENGTH_SYMBOL_TABLE[length]
}

/// Gets the amount of extra bits for the given dist, cfr. the DEFLATE spec.
pub const fn get_dist_extra_bits(dist: u16) -> u32 {
    if dist < 5 {
        return 0;
    }
    (dist - 1).ilog2() - 1
}

/// Gets value of the extra bits for the given dist, cfr. the DEFLATE spec.
pub const fn get_dist_extra_bits_value(dist: u16) -> u16 {
    if dist < 5 {
        return 0;
    }
    let l = (dist - 1).ilog2();
    (dist - (1 + (1 << l))) & ((1 << (l - 1)) - 1)
}

pub const fn get_dist_symbol(dist: u16) -> u16 {
    DIST_SYMBOL_TABLE[dist as usize] as u16
}

const fn build_dist_symbol_table() -> [u8; 32769] {
    let mut table = [0u8; 32769];
    let mut i: u32 = 1;
    while i <= 32768 {
        let dist = i as u16;
        table[i as usize] = if dist < 5 {
            dist.wrapping_sub(1) as u8
        } else {
            let l = (dist - 1).ilog2();
            let r = (((dist - 1) >> (l - 1)) & 1) as u32;
            (l * 2 + r) as u8
        };
        i += 1;
    }
    table
}

static DIST_SYMBOL_TABLE: [u8; 32769] = build_dist_symbol_table();

const LENGTH_EXTRA_BITS: [u32; 288 /* Originally, 259 entries */] = [
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
    2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
    3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
    4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 0, // Padding to 288 entries for reduced bounds checking
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
];

/// Gets the amount of extra bits for the given length, cfr. the DEFLATE spec.
pub const fn get_length_extra_bits(l: usize) -> u32 {
    LENGTH_EXTRA_BITS[l]
}

const LENGTH_EXTRA_BITS_VALUE: [u32; 288 /* Originally, 259 entries */] = [
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0,
    1, 2, 3, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4,
    5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
    10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 5,
    6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
    17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
    11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 0, 1, 2, 3,
    4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
    29, 30, 31, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
    23, 24, 25, 26, 27, 28, 29, 30, 0,
    // Padding to 288 entries for reduced bounds checking
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
];

/// Gets value of the extra bits for the given length, cfr. the DEFLATE spec.
pub const fn get_length_extra_bits_value(l: usize) -> u32 {
    LENGTH_EXTRA_BITS_VALUE[l]
}

const LENGTH_SYMBOL_EXTRA_BITS_TABLE: [u32; 29] = [
    0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0,
];

/// Gets the amount of extra bits for the given length symbol.
pub const fn get_length_symbol_extra_bits(s: usize) -> u32 {
    LENGTH_SYMBOL_EXTRA_BITS_TABLE[s - 257]
}

const DIST_SYMBOL_EXTRA_BITS_TABLE: [u32; 30] = [
    0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13,
    13,
];

/// Gets the amount of extra bits for the given distance symbol.
pub const fn get_dist_symbol_extra_bits(s: usize) -> u32 {
    DIST_SYMBOL_EXTRA_BITS_TABLE[s]
}