zopfli/
symbols.rs

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const LENGTH_SYMBOL_TABLE: [usize; 259] = [
    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,
];

/// Gets the symbol for the given length, cfr. the DEFLATE spec.
/// Returns symbol in range [257-285] (inclusive).
pub 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 fn get_dist_extra_bits(dist: u16) -> usize {
    (match dist {
        0..=4 => 0,
        5..=8 => 1,
        9..=16 => 2,
        17..=32 => 3,
        33..=64 => 4,
        65..=128 => 5,
        129..=256 => 6,
        257..=512 => 7,
        513..=1024 => 8,
        1025..=2048 => 9,
        2049..=4096 => 10,
        4097..=8192 => 11,
        8193..=16384 => 12,
        _ => 13,
    }) as usize
}

/// Gets value of the extra bits for the given dist, cfr. the DEFLATE spec.
pub fn get_dist_extra_bits_value(dist: u16) -> u16 {
    match dist {
        0..=4 => 0,
        5..=8 => (dist - 5) & 1,
        9..=16 => (dist - 9) & 3,
        17..=32 => (dist - 17) & 7,
        33..=64 => (dist - 33) & 15,
        65..=128 => (dist - 65) & 31,
        129..=256 => (dist - 129) & 63,
        257..=512 => (dist - 257) & 127,
        513..=1024 => (dist - 513) & 255,
        1025..=2048 => (dist - 1025) & 511,
        2049..=4096 => (dist - 2049) & 1023,
        4097..=8192 => (dist - 4097) & 2047,
        8193..=16384 => (dist - 8193) & 4095,
        _ => (dist - 16385) & 8191,
    }
}

pub fn get_dist_symbol(dist: u16) -> usize {
    (match dist {
        0..=4 => dist - 1,
        5..=6 => 4,
        7..=8 => 5,
        9..=12 => 6,
        13..=16 => 7,
        17..=24 => 8,
        25..=32 => 9,
        33..=48 => 10,
        49..=64 => 11,
        65..=96 => 12,
        97..=128 => 13,
        129..=192 => 14,
        193..=256 => 15,
        257..=384 => 16,
        385..=512 => 17,
        513..=768 => 18,
        769..=1024 => 19,
        1025..=1536 => 20,
        1537..=2048 => 21,
        2049..=3072 => 22,
        3073..=4096 => 23,
        4097..=6144 => 24,
        6145..=8192 => 25,
        8193..=12288 => 26,
        12289..=16384 => 27,
        16385..=24576 => 28,
        _ => 29,
    }) as usize
}

const LENGTH_EXTRA_BITS: [usize; 259] = [
    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,
];

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

const LENGTH_EXTRA_BITS_VALUE: [u32; 259] = [
    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,
];

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