Refactor eagle bigram key matching (#13714)

python/sglang/srt/mem_cache/utils.py

@@ -13,7 +13,7 @@
 # ==============================================================================
 """Common utilities."""
 
-from typing import Any, Optional, Tuple
+from typing import Any, List, Optional, Tuple
 
 import torch
 import triton
@@ -241,3 +241,13 @@ def maybe_init_custom_mem_pool(
         return init_mooncake_custom_mem_pool(device)
     else:
         return False, None, None
+
+
+def convert_to_bigram_key(tokens: List[int]) -> List[Tuple[int, int]]:
+    # EAGLE uses bigram keys in the radix tree since draft sequence is the one-token-shifted version of target
+    # [1, 2, 3, 4] -> [(1,2), (2,3), (3,4)]
+    if len(tokens) and isinstance(tokens[0], tuple):
+        return tokens
+    if len(tokens) < 2:
+        return []
+    return [(tokens[i], tokens[i + 1]) for i in range(len(tokens) - 1)]