rune_core/item/
internal.rs

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1use core::hash::{self, Hash};
2use core::str;
3
4use crate::alloc::alloc::Allocator;
5use crate::alloc::{self, Vec};
6
7// Types available.
8pub(super) const CRATE: Tag = Tag(0b00);
9pub(super) const STRING: Tag = Tag(0b01);
10pub(super) const ID: Tag = Tag(0b10);
11
12/// How many bits the type of a tag takes up.
13pub(super) const TYPE_BITS: usize = 2;
14/// Mask of the type of a tag.
15pub(super) const TYPE_MASK: usize = (0b1 << TYPE_BITS) - 1;
16/// Total tag size in bytes.
17pub(super) const TAG_BYTES: usize = 2;
18/// Max size of data stored.
19pub(super) const MAX_DATA: usize = 0b1 << (TAG_BYTES * 8 - TYPE_BITS);
20
21#[derive(PartialEq, Eq, Hash)]
22#[repr(transparent)]
23pub(super) struct Tag(pub(super) u8);
24
25/// Read a single byte.
26///
27/// # Panics
28///
29/// Panics if the byte is not available.
30pub(super) fn read_tag(content: &[u8]) -> (Tag, usize) {
31    let &[a, b] = content else {
32        panic!("expected two bytes");
33    };
34
35    let n = u16::from_ne_bytes([a, b]);
36    let n = usize::from(n);
37    (Tag((n & TYPE_MASK) as u8), n >> TYPE_BITS)
38}
39
40/// Helper function to write an identifier.
41///
42/// # Panics
43///
44/// Panics if the provided size cannot fit withing an identifier.
45pub(super) fn write_tag<A: Allocator>(
46    output: &mut Vec<u8, A>,
47    Tag(tag): Tag,
48    n: usize,
49) -> alloc::Result<()> {
50    let tag = usize::from(tag);
51
52    debug_assert!(tag <= TYPE_MASK);
53
54    debug_assert!(
55        n < MAX_DATA,
56        "item data overflow, index or string size larger than MAX_DATA"
57    );
58
59    if n >= MAX_DATA {
60        return Err(alloc::Error::CapacityOverflow);
61    }
62
63    let n = u16::try_from((n << TYPE_BITS) | tag).expect("tag out of bounds");
64    let buf = n.to_ne_bytes();
65    output.try_extend_from_slice(&buf[..])?;
66    Ok(())
67}
68
69/// Internal function to write only the crate of a component.
70pub(super) fn write_crate<A: Allocator>(s: &str, output: &mut Vec<u8, A>) -> alloc::Result<()> {
71    write_tag(output, CRATE, s.len())?;
72    output.try_extend_from_slice(s.as_bytes())?;
73    write_tag(output, CRATE, s.len())?;
74    Ok(())
75}
76
77/// Internal function to write only the string of a component.
78pub(super) fn write_str<A: Allocator>(s: &str, output: &mut Vec<u8, A>) -> alloc::Result<()> {
79    write_tag(output, STRING, s.len())?;
80    output.try_extend_from_slice(s.as_bytes())?;
81    write_tag(output, STRING, s.len())?;
82    Ok(())
83}
84
85/// Internal function to hash the given string.
86pub(super) fn hash_str<H>(string: &str, hasher: &mut H)
87where
88    H: hash::Hasher,
89{
90    STRING.hash(hasher);
91    string.hash(hasher);
92}
93
94pub(super) fn read_string(content: &[u8], n: usize) -> (&str, &[u8], &[u8]) {
95    let (buf, content) = content.split_at(n);
96
97    // consume the head tag.
98    let (tail_tag, content) = content.split_at(TAG_BYTES);
99
100    // Safety: we control the construction of the item.
101    let s = unsafe { str::from_utf8_unchecked(buf) };
102
103    (s, content, tail_tag)
104}
rune_core/item/internal.rs

rune_core/item/
internal.rs
