Fix whitespace catastrophic backtracking

tests/test_encoding.py

@@ -14,7 +14,7 @@
 @pytest.mark.parametrize("make_enc", ENCODING_FACTORIES)
 def test_extremely_big_encoding(make_enc: Callable[[], tiktoken.Encoding]):
     enc = make_enc()
-    for c in ["^", "0", "a", "'s"]: # TODO " ", "\n" are still failing
+    for c in ["^", "0", "a", "'s", " ", "\n"]:
         print(f"Validating `{c}`")
 
         big_value = c * 10_000

tiktoken_ext/openai_public.py

@@ -9,7 +9,7 @@
 # The pattern in the original GPT-2 release is:
 # r"""'s|'t|'re|'ve|'m|'ll|'d| ?[\p{L}]+| ?[\p{N}]+| ?[^\s\p{L}\p{N}]+|\s+(?!\S)|\s+"""
 # This is equivalent, but executes faster:
-_legacy_splitter_regex = r"""'(?:[sdmt]|ll|ve|re)| ?\p{L}++| ?\p{N}++| ?[^\s\p{L}\p{N}]++|\s+(?!\S)|\s++"""
+_legacy_splitter_regex = r"""'(?:[sdmt]|ll|ve|re)| ?\p{L}++| ?\p{N}++| ?[^\s\p{L}\p{N}]++|\s++$|\s+(?!\S)|\s"""
 
 
 def gpt2():
@@ -84,7 +84,7 @@ def cl100k_base():
     }
     return {
         "name": "cl100k_base",
-        "pat_str": r"""'(?i:[sdmt]|ll|ve|re)|[^\r\n\p{L}\p{N}]?+\p{L}++|\p{N}{1,3}+| ?[^\s\p{L}\p{N}]++[\r\n]*+|\s*[\r\n]|\s+(?!\S)|\s++""",
+        "pat_str": r"""'(?i:[sdmt]|ll|ve|re)|[^\r\n\p{L}\p{N}]?+\p{L}++|\p{N}{1,3}+| ?[^\s\p{L}\p{N}]++[\r\n]*+|\s++$|\s*[\r\n]|\s+(?!\S)|\s""",
         "mergeable_ranks": mergeable_ranks,
         "special_tokens": special_tokens,
     }