src/libcore/unicode/bool_trie.rs

   1 /// BoolTrie is a trie for representing a set of Unicode codepoints. It is
   2 /// implemented with postfix compression (sharing of identical child nodes),
   3 /// which gives both compact size and fast lookup.
   4 ///
   5 /// The space of Unicode codepoints is divided into 3 subareas, each
   6 /// represented by a trie with different depth. In the first (0..0x800), there
   7 /// is no trie structure at all; each u64 entry corresponds to a bitvector
   8 /// effectively holding 64 bool values.
   9 ///
  10 /// In the second (0x800..0x10000), each child of the root node represents a
  11 /// 64-wide subrange, but instead of storing the full 64-bit value of the leaf,
  12 /// the trie stores an 8-bit index into a shared table of leaf values. This
  13 /// exploits the fact that in reasonable sets, many such leaves can be shared.
  14 ///
  15 /// In the third (0x10000..0x110000), each child of the root node represents a
  16 /// 4096-wide subrange, and the trie stores an 8-bit index into a 64-byte slice
  17 /// of a child tree. Each of these 64 bytes represents an index into the table
  18 /// of shared 64-bit leaf values. This exploits the sparse structure in the
  19 /// non-BMP range of most Unicode sets.
  20 pub struct BoolTrie {
  21     // 0..0x800 (corresponding to 1 and 2 byte utf-8 sequences)
  22     pub r1: [u64; 32], // leaves
  23
  24     // 0x800..0x10000 (corresponding to 3 byte utf-8 sequences)
  25     pub r2: [u8; 992],      // first level
  26     pub r3: &'static [u64], // leaves
  27
  28     // 0x10000..0x110000 (corresponding to 4 byte utf-8 sequences)
  29     pub r4: [u8; 256],      // first level
  30     pub r5: &'static [u8],  // second level
  31     pub r6: &'static [u64], // leaves
  32 }
  33 impl BoolTrie {
  34     pub fn lookup(&self, c: char) -> bool {
  35         let c = c as u32;
  36         if c < 0x800 {
  37             trie_range_leaf(c, self.r1[(c >> 6) as usize])
  38         } else if c < 0x10000 {
  39             let child = self.r2[(c >> 6) as usize - 0x20];
  40             trie_range_leaf(c, self.r3[child as usize])
  41         } else {
  42             let child = self.r4[(c >> 12) as usize - 0x10];
  43             let leaf = self.r5[((child as usize) << 6) + ((c >> 6) as usize & 0x3f)];
  44             trie_range_leaf(c, self.r6[leaf as usize])
  45         }
  46     }
  47 }
  48
  49 pub struct SmallBoolTrie {
  50     pub(crate) r1: &'static [u8],  // first level
  51     pub(crate) r2: &'static [u64], // leaves
  52 }
  53
  54 impl SmallBoolTrie {
  55     pub fn lookup(&self, c: char) -> bool {
  56         let c = c as u32;
  57         match self.r1.get((c >> 6) as usize) {
  58             Some(&child) => trie_range_leaf(c, self.r2[child as usize]),
  59             None => false,
  60         }
  61     }
  62 }
  63
  64 fn trie_range_leaf(c: u32, bitmap_chunk: u64) -> bool {
  65     ((bitmap_chunk >> (c & 63)) & 1) != 0
  66 }