remove Arc<> for encoder hashmap and use directly (#12)

partial revert of #11

was seeing weird perf regression in benchmarks

rust borrow checker makes it really hard for two things to own the same
data, so take the simple way out by letting CoreBPE own mergeable_ranks

src/corebpe.rs

@@ -166,7 +166,7 @@ const MAX_NUM_THREADS: usize = 8;
 
 #[derive(Debug)]
 pub struct CoreBPE {
-    encoder: Arc<HashMap<Vec<u8>, usize>>,
+    pub encoder: HashMap<Vec<u8>, usize>,
     special_tokens_encoder: HashMap<String, usize>,
     decoder: HashMap<usize, Vec<u8>>,
     special_tokens_decoder: HashMap<usize, Vec<u8>>,
@@ -429,7 +429,7 @@ impl CoreBPE {
 
 impl CoreBPE {
     pub fn new(
-        encoder: Arc<HashMap<Vec<u8>, usize>>,
+        encoder: HashMap<Vec<u8>, usize>,
         special_tokens_encoder: HashMap<String, usize>,
         pattern: &str,
     ) -> Result<Self, fancy_regex::Error> {

src/encoding.rs

@@ -13,8 +13,6 @@ pub struct Encoding {
     pub name: String,
     /// The regular expression pattern used to split text into pieces.
     pat_str: String,
-    /// The map from mergeable byte sequences to their ranks.
-    mergeable_ranks: Arc<HashMap<Vec<u8>, usize>>,
     /// The maximum length of the keys in `mergeable_ranks`.
     mergeable_ranks_max_key_len: usize,
     /// All prefixes of the mergeable ranks. May or may not be tokens themselves!
@@ -64,7 +62,7 @@ impl Encoding {
     pub fn new(
         name: &str,
         pat_str: &str,
-        mergeable_ranks: Arc<HashMap<Vec<u8>, usize>>,
+        mergeable_ranks: HashMap<Vec<u8>, usize>,
         special_tokens: HashMap<String, usize>,
         explicit_n_vocab: Option<usize>,
     ) -> Result<Self, EncodingError> {
@@ -113,7 +111,6 @@ impl Encoding {
         Ok(Self {
             name: name.to_string(),
             pat_str: pat_str.to_string(),
-            mergeable_ranks,
             mergeable_ranks_max_key_len,
             prefixes_of_mergeable_ranks,
             special_tokens,
@@ -157,7 +154,7 @@ impl Encoding {
                 if current_token.len() > 1 {
                     new_current_token.clear();
                     new_current_token.push(current_token.pop().unwrap());
-                    while !self.mergeable_ranks.contains_key(&current_token) {
+                    while !self.core_bpe.encoder.contains_key(&current_token) {
                         if current_token.len() == 1 {
                             break;
                         }
@@ -177,14 +174,14 @@ impl Encoding {
             }
         }
 
-        while !self.mergeable_ranks.contains_key(&current_token) {
+        while !self.core_bpe.encoder.contains_key(&current_token) {
             if current_token.len() == 0 {
                 break;
             }
             if current_token.len() > 1 {
                 new_current_token.clear();
                 new_current_token.push(current_token.pop().unwrap());
-                while !self.mergeable_ranks.contains_key(&current_token) {
+                while !self.core_bpe.encoder.contains_key(&current_token) {
                     if current_token.len() == 1 {
                         break;
                     }

src/load.rs

@@ -5,7 +5,6 @@ use sha2::Sha256;
 // call its methods without adding to the namespace.
 use base64::engine::general_purpose::STANDARD as BASE64;
 use base64::engine::Engine as _;
-use std::sync::Arc;
 
 // define the error
 #[derive(Debug, Clone)]
@@ -17,7 +16,7 @@ pub enum Error {
 pub fn load_tiktoken_bpe(
     tiktoken_bpe_contents: &[u8],
     shasum: &str,
-) -> Result<Arc<HashMap<Vec<u8>, usize>>, Error> {
+) -> Result<HashMap<Vec<u8>, usize>, Error> {
     // check the shasum
     let mut hasher = Sha256::new();
     hasher.update(tiktoken_bpe_contents);
@@ -43,5 +42,5 @@ pub fn load_tiktoken_bpe(
         map.insert(token, rank);
     }
     map.shrink_to_fit();
-    Ok(Arc::new(map))
+    Ok(map)
 }