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use super::Pair;
use rand::{thread_rng, Rng};
use std::cmp::Ordering;
use std::collections::{BinaryHeap, HashMap};
#[derive(Debug, Eq)]
struct Merge {
pos: usize,
rank: u32,
new_id: u32,
}
impl PartialEq for Merge {
fn eq(&self, other: &Self) -> bool {
self.rank == other.rank && self.pos == other.pos
}
}
impl PartialOrd for Merge {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
// By manually implementing this, we make the containing BinaryHeap a
// min-heap ordered first on the rank, and the pos otherwise
if self.rank != other.rank {
Some(other.rank.cmp(&self.rank))
} else {
Some(other.pos.cmp(&self.pos))
}
}
}
impl Ord for Merge {
fn cmp(&self, other: &Self) -> Ordering {
self.partial_cmp(other).unwrap()
}
}
#[derive(Debug, Clone, Copy)]
struct Symbol {
c: u32,
prev: isize,
next: isize,
len: usize,
}
impl Symbol {
/// Merges the current Symbol with the other one.
/// In order to update prev/next, we consider Self to be the Symbol on the left,
/// and other to be the next one on the right.
pub fn merge_with(&mut self, other: &Self, new_c: u32) {
self.c = new_c;
self.len += other.len;
self.next = other.next;
}
}
#[derive(Clone, Default)]
pub(super) struct Word {
symbols: Vec<Symbol>,
}
impl std::fmt::Debug for Word {
fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
fmt.debug_struct("Word")
.field(
"chars",
&self
.symbols
.iter()
.map(|s| s.c.to_string())
.collect::<Vec<_>>()
.join(" "),
)
.field("symbols", &self.symbols)
.finish()
}
}
impl Word {
pub(super) fn new() -> Self {
Word { symbols: vec![] }
}
pub(super) fn with_capacity(capacity: usize) -> Self {
Self {
symbols: Vec::with_capacity(capacity),
}
}
pub(super) fn add(&mut self, c: u32, byte_len: usize) {
let (prev, next) = {
let len = self.symbols.len() as isize;
if let Some(last) = self.symbols.last_mut() {
// Update `next` on the previous one
last.next = len;
(len - 1, -1)
} else {
(-1, -1)
}
};
self.symbols.push(Symbol {
c,
prev,
next,
len: byte_len,
});
}
pub(super) fn merge(&mut self, c1: u32, c2: u32, replacement: u32) -> Vec<(Pair, i32)> {
let mut changes: Vec<(Pair, i32)> = vec![];
let mut i = 0;
loop {
if i >= self.symbols.len() {
break;
}
// Found a pair
if self.symbols[i].c == c1 && i + 1 < self.symbols.len() && self.symbols[i + 1].c == c2
{
let first = self.symbols[i];
let second = self.symbols[i + 1];
// If there are other characters before the pair
if i > 0 {
changes.push(((self.symbols[i - 1].c, first.c), -1));
changes.push(((self.symbols[i - 1].c, replacement), 1));
}
// Remove in place
let new_s = Symbol {
c: replacement,
prev: first.prev,
next: second.next,
len: first.len + second.len,
};
self.symbols.insert(i, new_s); // Insert replacement before first char of pair
self.symbols.remove(i + 1); // Remove first char of pair
self.symbols.remove(i + 1); // And then the second
// If there are other characters after the pair
if i < self.symbols.len() - 1 {
changes.push(((second.c, self.symbols[i + 1].c), -1));
changes.push(((replacement, self.symbols[i + 1].c), 1));
}
}
i += 1;
}
changes
}
pub(super) fn merge_all(&mut self, merges: &HashMap<Pair, (u32, u32)>, dropout: Option<f32>) {
let mut queue = BinaryHeap::with_capacity(self.symbols.len());
let mut skip = Vec::with_capacity(queue.len());
queue.extend(
self.symbols
.windows(2)
.enumerate()
.filter_map(|(index, window)| {
let pair = (window[0].c, window[1].c);
merges.get(&pair).map(|m| Merge {
pos: index,
rank: m.0,
new_id: m.1,
})
}),
);
while let Some(top) = queue.pop() {
if dropout
.map(|d| thread_rng().gen::<f32>() < d)
.unwrap_or(false)
{
skip.push(top);
} else {
// Re-insert the skipped elements
queue.extend(skip.drain(..));
if self.symbols[top.pos].len == 0 {
continue;
}
// Do nothing if we are the last symbol
if self.symbols[top.pos].next == -1 {
continue;
}
let next_pos = self.symbols[top.pos].next as usize;
let right = self.symbols[next_pos];
// Make sure we are not processing an expired queue entry
let target_new_pair = (self.symbols[top.pos].c, right.c);
if !merges
.get(&target_new_pair)
.map_or(false, |(_, new_id)| *new_id == top.new_id)
{
continue;
}
// Otherwise, let's merge
self.symbols[top.pos].merge_with(&right, top.new_id);
// Tag the right part as removed
self.symbols[next_pos].len = 0;
// Update `prev` on the new `next` to the current pos
if right.next > -1 && (right.next as usize) < self.symbols.len() {
self.symbols[right.next as usize].prev = top.pos as isize;
}
// Insert the new pair formed with the previous symbol
let current = &self.symbols[top.pos];
if current.prev >= 0 {
let prev = current.prev as usize;
let prev_symbol = self.symbols[prev];
let new_pair = (prev_symbol.c, current.c);
if let Some((rank, new_id)) = merges.get(&new_pair) {
queue.push(Merge {
pos: current.prev as usize,
rank: *rank,
new_id: *new_id,
});
}
}
// Insert the new pair formed with the next symbol
let next = current.next as usize;
if next < self.symbols.len() {
let next_symbol = self.symbols[next];
let new_pair = (current.c, next_symbol.c);
if let Some((rank, new_id)) = merges.get(&new_pair) {
queue.push(Merge {
pos: top.pos,
rank: *rank,
new_id: *new_id,
});
}
}
}
}
// Filter out the removed symbols
self.symbols.retain(|s| s.len != 0);
}
pub(super) fn get_chars(&self) -> Vec<u32> {
self.symbols.iter().map(|s| s.c).collect()
}
pub(super) fn get_chars_iter(&self) -> impl Iterator<Item = u32> + '_ {
self.symbols.iter().map(|s| s.c)
}
pub(super) fn get_offsets_iter(&self) -> impl Iterator<Item = (usize, usize)> + '_ {
let mut pos = 0;
self.symbols.iter().map(move |symbol| {
let new_pos = pos + symbol.len;
let offset = (pos, new_pos);
pos = new_pos;
offset
})
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_merge() {
// Let's say we have the word 'hello' and a word-to-id vocab that looks
// like this: {'h': 0, 'e': 1, 'l': 2, 'o': 3}.
let mut word = Word::new();
word.add(0, 1); // 'h'
word.add(1, 1); // 'e'
word.add(2, 1); // 'l'
word.add(2, 1); // 'l'
word.add(3, 1); // 'o'
// We're going to perform a merge on the pair ('l', 'l') ~= (2, 2). Let's
// say that 'll' has the ID of 4 in the updated word-to-id vocab.
let changes = word.merge(2, 2, 4);
// So the word should now look like this:
assert_eq!(
word.get_chars(),
&[
0u32, // 'h'
1u32, // 'e'
4u32, // 'll'
3u32, // 'o'
]
);
// The return value `changes` will be used to update the pair counts during
// training. This merge affects the counts for the pairs
// ('e', 'l') ~= (1, 2),
// ('e', 'll') ~= (1, 4),
// ('l', 'o') ~= (2, 3), and
// ('ll', 'o') ~= (4, 3).
// So the changes should reflect that:
assert_eq!(
changes,
&[
((1u32, 2u32), -1i32), // count for ('e', 'l') should be decreased by 1.
((1u32, 4u32), 1i32), // count for ('e', 'll') should be increased by 1.
((2u32, 3u32), -1i32), // count for ('l', 'o') should be decreased by 1.
((4u32, 3u32), 1i32), // count for ('ll', 'o') should be increased by 1.
]
);
}
}