zstd-complete 0.3.0

A pure Rust Zstandard compressor and decompressor with bounded streaming I/O
Documentation 
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
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146

#[derive(Clone, Copy)]
struct SmallLengthCode {
    add_bits: u32,
    code: u8,
    num_bits: u8,
}

const _: () = assert!(core::mem::size_of::<SmallLengthCode>() == 8);

const LITERAL_LENGTH_SMALL_CODES: [SmallLengthCode; 64] = small_literal_length_codes();
const MATCH_LENGTH_SMALL_CODES: [SmallLengthCode; 128] = small_match_length_codes();

#[inline(always)]
pub(crate) fn literal_length_code(len: u32) -> u8 {
    encode_literal_length(len).0
}

#[inline(always)]
pub(crate) fn match_length_code(len: u32) -> u8 {
    encode_match_len(len).0
}

#[inline(always)]
pub(crate) fn offset_code(offset_value: u32) -> u8 {
    encode_offset(offset_value).0
}

#[inline(always)]
pub(super) fn encode_literal_length(len: u32) -> (u8, u32, usize) {
    if len < LITERAL_LENGTH_SMALL_CODES.len() as u32 {
        let entry = LITERAL_LENGTH_SMALL_CODES[len as usize];
        return (entry.code, entry.add_bits, usize::from(entry.num_bits));
    }

    match len {
        0..=63 => unreachable!(),
        64..=127 => (25, len - 64, 6),
        128..=255 => (26, len - 128, 7),
        256..=511 => (27, len - 256, 8),
        512..=1023 => (28, len - 512, 9),
        1024..=2047 => (29, len - 1024, 10),
        2048..=4095 => (30, len - 2048, 11),
        4096..=8191 => (31, len - 4096, 12),
        8192..=16383 => (32, len - 8192, 13),
        16384..=32767 => (33, len - 16384, 14),
        32768..=65535 => (34, len - 32768, 15),
        65536..=131071 => (35, len - 65536, 16),
        131072.. => unreachable!(),
    }
}

#[inline(always)]
pub(super) fn encode_match_len(len: u32) -> (u8, u32, usize) {
    if (3..=130).contains(&len) {
        let entry = MATCH_LENGTH_SMALL_CODES[(len - 3) as usize];
        return (entry.code, entry.add_bits, usize::from(entry.num_bits));
    }

    match len {
        0..=2 => unreachable!(),
        3..=130 => unreachable!(),
        131..=258 => (43, len - 131, 7),
        259..=514 => (44, len - 259, 8),
        515..=1026 => (45, len - 515, 9),
        1027..=2050 => (46, len - 1027, 10),
        2051..=4098 => (47, len - 2051, 11),
        4099..=8194 => (48, len - 4099, 12),
        8195..=16386 => (49, len - 8195, 13),
        16387..=32770 => (50, len - 16387, 14),
        32771..=65538 => (51, len - 32771, 15),
        65539..=131074 => (52, len - 65539, 16),
        131075.. => unreachable!(),
    }
}

const fn small_literal_length_codes() -> [SmallLengthCode; 64] {
    let mut codes = [SmallLengthCode {
        add_bits: 0,
        code: 0,
        num_bits: 0,
    }; 64];
    let mut len = 0usize;
    while len < codes.len() {
        let (code, add_bits, num_bits) = match len {
            0..=15 => (len as u8, 0, 0),
            16..=17 => (16, len as u32 - 16, 1),
            18..=19 => (17, len as u32 - 18, 1),
            20..=21 => (18, len as u32 - 20, 1),
            22..=23 => (19, len as u32 - 22, 1),
            24..=27 => (20, len as u32 - 24, 2),
            28..=31 => (21, len as u32 - 28, 2),
            32..=39 => (22, len as u32 - 32, 3),
            40..=47 => (23, len as u32 - 40, 3),
            48..=63 => (24, len as u32 - 48, 4),
            _ => unreachable!(),
        };
        codes[len] = SmallLengthCode {
            add_bits,
            code,
            num_bits: num_bits as u8,
        };
        len += 1;
    }
    codes
}

const fn small_match_length_codes() -> [SmallLengthCode; 128] {
    let mut codes = [SmallLengthCode {
        add_bits: 0,
        code: 0,
        num_bits: 0,
    }; 128];
    let mut idx = 0usize;
    while idx < codes.len() {
        let len = idx + 3;
        let (code, add_bits, num_bits) = match len {
            3..=34 => (len as u8 - 3, 0, 0),
            35..=36 => (32, len as u32 - 35, 1),
            37..=38 => (33, len as u32 - 37, 1),
            39..=40 => (34, len as u32 - 39, 1),
            41..=42 => (35, len as u32 - 41, 1),
            43..=46 => (36, len as u32 - 43, 2),
            47..=50 => (37, len as u32 - 47, 2),
            51..=58 => (38, len as u32 - 51, 3),
            59..=66 => (39, len as u32 - 59, 3),
            67..=82 => (40, len as u32 - 67, 4),
            83..=98 => (41, len as u32 - 83, 4),
            99..=130 => (42, len as u32 - 99, 5),
            _ => unreachable!(),
        };
        codes[idx] = SmallLengthCode {
            add_bits,
            code,
            num_bits: num_bits as u8,
        };
        idx += 1;
    }
    codes
}

#[inline(always)]
pub(super) fn encode_offset(len: u32) -> (u8, u32, usize) {
    let log = len.ilog2();
    let lower = len & ((1 << log) - 1);
    (log as u8, lower, log as usize)
}