Merge pull request #13 from github/aneubeck/dict

Add constructor from dictionary and count_till_limit function

Author: aneubeck

crates/bpe/src/byte_pair_encoding.rs

@@ -2,7 +2,6 @@ use std::cmp::Reverse;
 use std::collections::BinaryHeap;
 use std::hash::{Hash, Hasher};
 use std::ops::Range;
-use std::time::Instant;
 
 use daachorse::{DoubleArrayAhoCorasick, DoubleArrayAhoCorasickBuilder};
 use fnv::{FnvHashMap, FnvHasher};
@@ -181,32 +180,32 @@ impl BytePairEncoding {
         &BPE_CL100K
     }
 
+    /// Construct a BytePairEncoding instance frmo a tiktoken dictionary.
     pub fn from_tiktoken(tiktoken_bpe: &CoreBPE, num_tokens: usize) -> Self {
-        let start = Instant::now();
-        println!("loaded tiktoken: {:?}", start.elapsed());
+        Self::from_dictionary((0..num_tokens).map(|i| tiktoken_bpe._decode_native(&[i])))
+    }
+
+    /// Construct a BytePairEncoding instance from an iterator which enumerates all tokens.
+    pub fn from_dictionary(iter: impl Iterator<Item = Vec<u8>>) -> Self {
         let mut all_tokens = Vec::new();
         let mut all_tokens_rev = Vec::new();
         let mut token_starts = vec![0];
         let mut bytes_hash_to_token = FnvHashMap::default();
-        for i in 0..num_tokens {
-            let token = tiktoken_bpe._decode_native(&[i]);
+        for (i, token) in iter.enumerate() {
             bytes_hash_to_token.insert(hash_bytes(&token), i as u32);
             all_tokens_rev.extend(token.iter().copied().rev());
             all_tokens.extend(token);
             token_starts.push(all_tokens.len() as u32);
         }
         assert_eq!(bytes_hash_to_token.len() + 1, token_starts.len());
-        println!("copied tokens: {:?}", start.elapsed());
 
         let longest_searcher = DoubleArrayAhoCorasickBuilder::new()
             .match_kind(daachorse::MatchKind::LeftmostLongest)
             .build(token_iter(&all_tokens, &token_starts))
             .expect("failed to build AhoCorasick");
-        println!("constructed longest searcher: {:?}", start.elapsed());
 
         let overlapping_searcher =
             DoubleArrayAhoCorasick::<u32>::new(token_iter(&all_tokens, &token_starts)).expect("");
-        println!("constructed overlapping searcher: {:?}", start.elapsed());
         let overlapping_searcher_rev =
             DoubleArrayAhoCorasick::<u32>::new(token_iter(&all_tokens_rev, &token_starts))
                 .expect("");
@@ -216,7 +215,6 @@ impl BytePairEncoding {
                 next_match(&longest_searcher, &token[0..token.len() - 1]).unwrap_or(u32::MAX)
             })
             .collect();
-        println!("constructed next_prefix_match: {:?}", start.elapsed());
 
         let mut split_table = vec![];
         let mut pair_lookup = FnvHashMap::default();
@@ -243,8 +241,6 @@ impl BytePairEncoding {
                 split_table.push((id as u32, id as u32));
             }
         }
-        println!("constructed split table: {:?}", start.elapsed());
-
         Self {
             all_tokens,
             token_starts,
@@ -339,12 +335,35 @@ impl BytePairEncoding {
         last_token
     }
 
+    /// Counts the number tokens produced when encoding the text.
     pub fn count(&self, text: &[u8]) -> usize {
         let mut enc = BacktrackEncoder::new(self, text);
         while enc.step().is_some() {}
         enc.count()
     }
 
+    /// Returns the token count iff the total token count stays below the specified `token_limit`.
+    /// Otherwise, it returns false.
+    /// This function can be faster than `count` when the token_limit is much smaller than the provided text.
+    pub fn count_till_limit(&self, text: &[u8], token_limit: usize) -> Option<usize> {
+        let mut enc = BacktrackEncoder::new(self, text);
+        // When the text has exactly the desired number of tokens, then it could in theory happen that
+        // the token_limit is exceeded before the end of the text is reached (and a different encoding is tested).
+        // To be on the "safe" side, we add a little buffer for such cases.
+        // TODO: Determine exactly how large this buffer must be in the worst case.
+        let limit_with_buffer = token_limit.saturating_add(10);
+        while enc.step().is_some() {
+            if enc.count() > limit_with_buffer {
+                return None;
+            }
+        }
+        if enc.count() <= token_limit {
+            Some(enc.count())
+        } else {
+            None
+        }
+    }
+
     pub fn encode_via_table(&self, text: &[u8]) -> Vec<u32> {
         let last_token = self.encode_all_prefixes(text);
         let mut encoded = Vec::with_capacity(text.len() / 3);