mopenzl 0.2.3

OpenZL compression and decompression in safe Rust; encoding is byte-identical to Meta's reference library
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

//! Decoder of the `parse_int` feature: `parse_int` (60).
//!
//! Ports `codecs/parse_int/decode_parse_int_binding.c` and
//! `decode_parse_int_kernel.c`. The input is a numeric stream of 64-bit
//! signed integers; each becomes its canonical decimal string (no leading
//! zeros, no `+`, a single `-` when negative). The C kernel formats four
//! digits at a time from a lookup table, backwards; the result is the same
//! as plain division, which is what is used here.

use super::{Ctx, Desc};
use crate::decompressor::core::data::{Input, Stream, Type, corrupt};
use crate::decompressor::error::DecodeError;

/// `ZL_StandardTransformID_parse_int`: integers back to decimal strings.
pub(crate) const PARSE_INT: Desc = Desc {
    id: 60,
    min_version: 19,
    regens: &[Type::String],
    variable_regens: false,
    inputs: &[Type::Numeric],
    variable_inputs: 0,
    decode,
};

/// Characters of the decimal form of `value`: digits plus the sign.
const fn text_len(value: i64) -> usize {
    let digits = match value.unsigned_abs().checked_ilog10() {
        Some(log) => log as usize + 1,
        None => 1,
    };
    digits + (value < 0) as usize
}

/// `DI_parseInt`.
fn decode(_: &mut Ctx<'_>, inputs: &[Input<'_>], regens: &mut [Stream]) -> Result<(), DecodeError> {
    let numbers = &inputs[0];
    if numbers.width != 8 {
        return Err(corrupt());
    }
    let values = || {
        numbers
            .bytes
            .as_chunks::<8>()
            .0
            .iter()
            .map(|n| i64::from_le_bytes(*n))
    };
    let total = values().map(text_len).try_fold(0usize, usize::checked_add);
    let (bytes, lens) = regens[0].strings(numbers.len(), total.ok_or_else(corrupt)?)?;
    for value in values() {
        let start = bytes.len();
        if value < 0 {
            bytes.push(b'-');
        }
        let mut magnitude = value.unsigned_abs();
        let mut digits = [0u8; 20];
        let mut at = digits.len();
        loop {
            at -= 1;
            digits[at] = b'0' + (magnitude % 10) as u8;
            magnitude /= 10;
            if magnitude == 0 {
                break;
            }
        }
        bytes.extend_from_slice(&digits[at..]);
        lens.push((bytes.len() - start) as u32);
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::super::State;
    use super::*;
    use crate::Backend;
    use alloc::string::{String, ToString};
    use alloc::vec::Vec;

    fn run(width: usize, bytes: &[u8], budget: usize) -> Result<Stream, DecodeError> {
        let mut state = State::new(Backend::default());
        let mut ctx = Ctx::new(&mut state, &[]);
        let mut regens = [Stream::default()];
        regens[0].prepare(Type::String, budget);
        let input = Input {
            ty: Type::Numeric,
            width,
            bytes,
            lens: &[],
        };
        (PARSE_INT.decode)(&mut ctx, &[input], &mut regens)?;
        let [stream] = regens;
        stream.validate()?;
        Ok(stream)
    }

    #[test]
    fn integers_become_canonical_decimals() {
        let values = [
            0i64,
            1,
            -1,
            9,
            10,
            99,
            100,
            12345,
            -12345,
            9_999_999_999,
            i64::MAX,
            i64::MIN,
            i64::MIN + 1,
            1_000_000_000_000_000_000,
        ];
        let bytes: Vec<u8> = values.iter().flat_map(|v| v.to_le_bytes()).collect();
        let out = run(8, &bytes, 1 << 10).unwrap();
        let text: String = values.iter().map(i64::to_string).collect();
        assert_eq!(out.bytes(), text.as_bytes());
        let lens: Vec<u32> = values.iter().map(|v| v.to_string().len() as u32).collect();
        assert_eq!(out.as_input().lens, lens);
    }

    #[test]
    fn empty_streams_and_bad_inputs() {
        assert!(run(8, &[], 0).unwrap().as_input().lens.is_empty());
        // Only 64-bit numbers parse.
        assert!(run(4, &[0; 8], 1 << 10).is_err());
        // The output is bounded by the budget.
        let bytes = 123456i64.to_le_bytes();
        assert!(run(8, &bytes, 9).is_err());
        assert!(run(8, &bytes, 10).is_ok());
    }
}