1 // Copyright 2014 The Servo Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
3 //
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
9 
10 /// A static `PhfStrSet`
11 ///
12 /// This trait is implemented by static sets of interned strings generated using
13 /// `string_cache_codegen`, and `EmptyStaticAtomSet` for when strings will be added dynamically.
14 ///
15 /// It is used by the methods of [`Atom`] to check if a string is present in the static set.
16 ///
17 /// [`Atom`]: struct.Atom.html
18 pub trait StaticAtomSet: Ord {
19     /// Get the location of the static string set in the binary.
get() -> &'static PhfStrSet20     fn get() -> &'static PhfStrSet;
21     /// Get the index of the empty string, which is in every set and is used for `Atom::default`.
empty_string_index() -> u3222     fn empty_string_index() -> u32;
23 }
24 
25 /// A string set created using a [perfect hash function], specifically
26 /// [Hash, Displace and Compress].
27 ///
28 /// See the CHD document for the meaning of the struct fields.
29 ///
30 /// [perfect hash function]: https://en.wikipedia.org/wiki/Perfect_hash_function
31 /// [Hash, Displace and Compress]: http://cmph.sourceforge.net/papers/esa09.pdf
32 pub struct PhfStrSet {
33     #[doc(hidden)]
34     pub key: u64,
35     #[doc(hidden)]
36     pub disps: &'static [(u32, u32)],
37     #[doc(hidden)]
38     pub atoms: &'static [&'static str],
39     #[doc(hidden)]
40     pub hashes: &'static [u32],
41 }
42 
43 /// An empty static atom set for when only dynamic strings will be added
44 #[derive(PartialEq, Eq, PartialOrd, Ord)]
45 pub struct EmptyStaticAtomSet;
46 
47 impl StaticAtomSet for EmptyStaticAtomSet {
get() -> &'static PhfStrSet48     fn get() -> &'static PhfStrSet {
49         // The name is a lie: this set is not empty (it contains the empty string)
50         // but that’s only to avoid divisions by zero in rust-phf.
51         static SET: PhfStrSet = PhfStrSet {
52             key: 0,
53             disps: &[(0, 0)],
54             atoms: &[""],
55             // "" SipHash'd, and xored with u64_hash_to_u32.
56             hashes: &[0x3ddddef3],
57         };
58         &SET
59     }
60 
empty_string_index() -> u3261     fn empty_string_index() -> u32 {
62         0
63     }
64 }
65