[Rerank] Early-exit logprob scan and hoist math import (#25046)

python/sglang/srt/entrypoints/openai/serving_rerank.py

@@ -1,5 +1,6 @@
 import heapq
 import logging
+import math
 from typing import Any, Dict, List, Optional, Union
 
 from fastapi import Request
@@ -533,8 +534,6 @@ class OpenAIServingRerank(OpenAIServingBase):
 
     def _extract_score_from_logprobs(self, ret: Dict[str, Any]) -> float:
         """Extract reranking score from generation response with logprobs."""
-        import math
-
         # Get logprobs from the response
         meta_info = ret.get("meta_info", {})
         output_top_logprobs = meta_info.get("output_top_logprobs", [])
@@ -546,13 +545,19 @@ class OpenAIServingRerank(OpenAIServingBase):
         # Format: list of tuples (logprob, token_id, token_text)
         p_yes = 0.0
         p_no = 0.0
+        found_yes = False
+        found_no = False
 
         for item in top_logprobs:
             logprob, token_id = item[0], item[1]
             if token_id == self._yes_token_id:
                 p_yes = math.exp(logprob)
+                found_yes = True
             elif token_id == self._no_token_id:
                 p_no = math.exp(logprob)
+                found_no = True
+            if found_yes and found_no:
+                break
 
         return _qwen3_rerank_score(p_yes, p_no)