fix text_offset of multi-token characters (#1037)

* fix text_offsets for bytes tokens

* fix

Author: twaka

llama_cpp/llama.py

@@ -1551,7 +1551,9 @@ def logit_bias_processor(
                             "utf-8", errors="ignore"
                         )
                         text_offset = len(prompt) + len(
-                            self.detokenize(completion_tokens[:returned_tokens])
+                            self.detokenize(completion_tokens[:returned_tokens]).decode(
+                                "utf-8", errors="ignore"
+                            )
                         )
                         token_offset = len(prompt_tokens) + returned_tokens
                         logits = self._scores[token_offset - 1, :]
@@ -1789,13 +1791,19 @@ def logit_bias_processor(
             ]
             all_logprobs = Llama.logits_to_logprobs(self._scores)[token_offset:]
             # TODO: may be able to change this loop to use np.take_along_dim
-            for token, token_str, logprobs_token in zip(
-                all_tokens, all_token_strs, all_logprobs
+            for idx, (token, token_str, logprobs_token) in enumerate(
+                zip(all_tokens, all_token_strs, all_logprobs)
             ):
                 if token == self.token_bos():
                     continue
-                text_offsets.append(text_offset)
-                text_offset += len(token_str)
+                text_offsets.append(
+                    text_offset
+                    + len(
+                        self.detokenize(all_tokens[:idx]).decode(
+                            "utf-8", errors="ignore"
+                        )
+                    )
+                )
                 tokens.append(token_str)
                 sorted_logprobs = list(
                     sorted(