chess/
cache_table.rs

1#[derive(Copy, Clone, PartialEq, PartialOrd)]
2struct CacheTableEntry<T: Copy + Clone + PartialEq + PartialOrd> {
3    hash: u64,
4    entry: T,
5}
6
7/// Store a cache of entries, each with an associated hash.
8pub struct CacheTable<T: Copy + Clone + PartialEq + PartialOrd> {
9    table: Box<[CacheTableEntry<T>]>,
10    mask: usize,
11}
12
13impl<T: Copy + Clone + PartialEq + PartialOrd> CacheTable<T> {
14    /// Create a new `CacheTable` with each associated entry initialized with a hash of '0'
15    /// Note: You must pass in a size where only 1 bit is set. (AKA: 2, 4, 8, 16, 1024, 65536,
16    /// etc.)
17    /// Panics when size is invalid.
18    #[inline]
19    pub fn new(size: usize, default: T) -> CacheTable<T> {
20        if size.count_ones() != 1 {
21            panic!("You cannot create a CacheTable with a non-binary number.");
22        }
23        let values = vec![
24            CacheTableEntry {
25                hash: 0,
26                entry: default
27            };
28            size
29        ];
30        CacheTable {
31            table: values.into_boxed_slice(),
32            mask: size - 1,
33        }
34    }
35
36    /// Get a particular entry with the hash specified
37    #[inline]
38    pub fn get(&self, hash: u64) -> Option<T> {
39        let entry = unsafe { *self.table.get_unchecked((hash as usize) & self.mask) };
40        if entry.hash == hash {
41            Some(entry.entry)
42        } else {
43            None
44        }
45    }
46
47    /// Add (or overwrite) an entry with the associated hash
48    #[inline]
49    pub fn add(&mut self, hash: u64, entry: T) {
50        let e = unsafe { self.table.get_unchecked_mut((hash as usize) & self.mask) };
51        *e = CacheTableEntry {
52            hash: hash,
53            entry: entry,
54        };
55    }
56
57    /// Replace an entry in the hash table with a user-specified replacement policy specified by
58    /// `replace`. The `replace` closure is called with the previous entry occupying the hash table
59    /// slot, and returns true or false to specify whether the entry should be replaced. Note that
60    /// the previous entry may not have the same hash, but merely be the default initialization or
61    /// a hash collision with `hash`.
62    ///
63    /// ```
64    /// use chess::CacheTable;
65    ///
66    /// # fn main() {
67    ///
68    /// let mut table: CacheTable<char> = CacheTable::new(256, 'a');
69    ///
70    /// assert_eq!(table.get(5), None);
71    /// // Note that 'a' is the default initialization value.
72    /// table.replace_if(5, 'b', |old_entry| old_entry != 'a');
73    /// assert_eq!(table.get(5), None);
74    /// table.replace_if(5, 'c', |old_entry| old_entry == 'a');
75    /// assert_eq!(table.get(5), Some('c'));
76    /// table.replace_if(5, 'd', |old_entry| old_entry == 'c');
77    /// assert_eq!(table.get(5), Some('d'));
78    ///
79    /// # }
80    /// ```
81    #[inline(always)]
82    pub fn replace_if<F: Fn(T) -> bool>(&mut self, hash: u64, entry: T, replace: F) {
83        let e = unsafe { self.table.get_unchecked_mut((hash as usize) & self.mask) };
84        if replace(e.entry) {
85            *e = CacheTableEntry {
86                hash: hash,
87                entry: entry,
88            };
89        }
90    }
91}
chess/cache_table.rs

chess/
cache_table.rs
