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use std::collections::HashMap;
use crate::regex::byte_range::ByteRange;
pub struct DecisionTree<T> {
instrs: Vec<Instr>,
ret_vals: Vec<T>,
}
#[repr(u32)]
#[derive(Copy, Clone)]
enum Instr {
JumpIfGe(u8, u8),
Ret(u8),
}
impl<T: Clone> DecisionTree<T> {
pub fn decide(&self, val: u8) -> T {
let mut pc = 0;
loop {
match self.instrs[pc] {
Instr::JumpIfGe(pivot, rela) => {
if val >= pivot {
pc += rela as usize;
} else {
pc += 1;
}
}
Instr::Ret(idx) => return self.ret_vals[idx as usize].clone(),
}
}
}
}
impl<T: PartialEq + Clone> DecisionTree<T> {
fn add_retval(&mut self, searched_val: &T) -> u8 {
for (i, val) in self.ret_vals.iter().enumerate() {
if val == searched_val {
return i as u8;
}
}
self.ret_vals.push(searched_val.clone());
(self.ret_vals.len() - 1) as u8
}
fn merge(mut self, other: Self) -> Self {
for ins in other.instrs.into_iter() {
match ins {
Instr::JumpIfGe(_, _) => self.instrs.push(ins),
Instr::Ret(i) => {
let i = self.add_retval(&other.ret_vals[i as usize]);
self.instrs.push(Instr::Ret(i));
}
}
}
self
}
fn build_inner(ranges: &[(ByteRange, T)]) -> Self {
assert!(!ranges.is_empty());
if ranges.len() == 1 {
Self {
instrs: vec![Instr::Ret(0)],
ret_vals: vec![ranges[0].1.clone()],
}
} else {
let pivot = ranges.len() / 2;
let a = Self::build_inner(&ranges[..pivot]);
let b = Self::build_inner(&ranges[pivot..]);
let decider = Self {
instrs: vec![Instr::JumpIfGe(
ranges[pivot].0.lower_bound(),
a.instrs.len() as u8 + 1,
)],
ret_vals: Vec::new(),
};
decider.merge(a).merge(b)
}
}
pub fn build(map: HashMap<ByteRange, T>, default: T) -> Self {
let mut ranges: Vec<ByteRange> = map.keys().cloned().collect();
ranges.push(ByteRange::all());
let ranges = ByteRange::split_to_disjoint(ranges);
for i in 0..ranges.len() - 1 {
assert_eq!(ranges[i].upper_bound() + 1, ranges[i + 1].lower_bound());
}
let ranges: Vec<(ByteRange, T)> = ranges
.into_iter()
.map(|r| {
let maps_to = map
.iter()
.filter_map(|(x, t)| if x.overlaps(r) { Some(t.clone()) } else { None })
.next()
.unwrap_or(default.clone());
(r, maps_to)
})
.collect();
Self::build_inner(&ranges)
}
}
impl<T> Default for DecisionTree<T> {
fn default() -> Self {
Self {
instrs: Default::default(),
ret_vals: Default::default(),
}
}
}
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