forked from mirrors/kingfisher
116 lines
3 KiB
Rust
116 lines
3 KiB
Rust
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use std::{
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collections::{hash_map::Entry, HashMap},
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ops::Range,
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};
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use bstr::{BStr, BString};
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/// A symbolic range pointing into a `BStringTable` buffer.
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#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
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pub struct Symbol<T> {
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i: T,
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j: T,
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}
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/// Convert between `Symbol` and `Range<usize>`.
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pub trait SymbolType: Copy + Eq + std::hash::Hash {
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fn to_range(self) -> Range<usize>;
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fn from_range(range: Range<usize>) -> Self;
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}
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impl SymbolType for Symbol<usize> {
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#[inline]
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fn to_range(self) -> Range<usize> {
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self.i..self.j
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}
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#[inline]
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fn from_range(range: Range<usize>) -> Self {
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Symbol { i: range.start, j: range.end }
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}
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}
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impl SymbolType for Symbol<u32> {
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#[inline]
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fn to_range(self) -> Range<usize> {
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(self.i as usize)..(self.j as usize)
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}
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#[inline]
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fn from_range(range: Range<usize>) -> Self {
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Symbol {
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i: range.start.try_into().expect("start fits in u32"),
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j: range.end.try_into().expect("end fits in u32"),
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}
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}
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}
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/// Interns `BString` values in one contiguous byte buffer.
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#[derive(Default)]
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pub struct BStringTable<S = Symbol<u32>> {
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storage: Vec<u8>,
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mapping: HashMap<BString, S>,
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}
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impl<S: SymbolType> BStringTable<S> {
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/// Default: ~32 KB symbols, ~1 MB bytes.
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#[inline]
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pub fn new() -> Self {
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Self::with_capacity(32 * 1024, 1024 * 1024)
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}
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/// Reserve space for `num_symbols` entries and `total_bytes` of storage.
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pub fn with_capacity(num_symbols: usize, total_bytes: usize) -> Self {
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BStringTable {
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storage: Vec::with_capacity(total_bytes),
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mapping: HashMap::with_capacity(num_symbols),
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}
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}
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/// Interns `s`, returning an existing or new symbol.
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#[inline]
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#[must_use]
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pub fn get_or_intern(&mut self, s: BString) -> S {
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match self.mapping.entry(s) {
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Entry::Occupied(e) => *e.get(),
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Entry::Vacant(e) => {
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let key = e.key();
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let start = self.storage.len();
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let end = start + key.len();
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self.storage.extend_from_slice(key.as_slice());
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*e.insert(S::from_range(start..end))
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}
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}
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}
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/// Look up the `BStr` slice for `symbol`.
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#[inline]
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#[must_use]
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pub fn resolve(&self, symbol: S) -> &BStr {
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let range = symbol.to_range();
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BStr::new(&self.storage[range])
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}
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}
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#[cfg(test)]
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mod tests {
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use pretty_assertions::{assert_eq, assert_ne};
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use super::*;
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#[test]
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fn simple_roundtrip() {
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let mut table: BStringTable = BStringTable::new();
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let a = BStr::new("foo");
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let b = BStr::new("bar");
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let s1 = table.get_or_intern(a.into());
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let s1a = table.get_or_intern(a.into());
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assert_eq!(s1, s1a);
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let s2 = table.get_or_intern(b.into());
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assert_ne!(s1, s2);
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assert_eq!(a, table.resolve(s1));
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assert_eq!(b, table.resolve(s2));
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}
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}
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