Fix access violation exception

Author: apsonawane

operators/tokenizer/ugm_kernels.hpp

@@ -521,8 +521,21 @@ struct SpmUgmTokenizer {
       if (longest_prefix_offset >= prefix_replacements_size_) {
         ORTX_CXX_API_THROW("[UgmTok]Index out of array bounds in precompiled charsmap!", ORT_RUNTIME_EXCEPTION);
       }
+      // Validate that we have valid prefix_replacements_ data
+      if (prefix_replacements_ == nullptr || prefix_replacements_size_ == 0) {
+        ORTX_CXX_API_THROW("[UgmTok]prefix_replacements_ is null or empty!", ORT_RUNTIME_EXCEPTION);
+      }
       const char* prefix_replacement = &prefix_replacements_[longest_prefix_offset];
-      return {prefix_replacement, static_cast<int>(longest_prefix_length)};
+      // Calculate safe length: find null terminator within remaining buffer
+      size_t max_len = prefix_replacements_size_ - longest_prefix_offset;
+      size_t replacement_len = 0;
+      while (replacement_len < max_len && prefix_replacement[replacement_len] != '\0') {
+        replacement_len++;
+      }
+      if (replacement_len == max_len) {
+        ORTX_CXX_API_THROW("[UgmTok]Replacement string not null-terminated in precompiled charsmap!", ORT_RUNTIME_EXCEPTION);
+      }
+      return {std::string_view(prefix_replacement, replacement_len), static_cast<int>(longest_prefix_length)};
     } else {
       // if yes, return this sequence unmodified
       size_t prefix_offset = ustring::UTF8Len(input_view[0]);
@@ -674,8 +687,21 @@ struct SpmUgmTokenizer {
       if (longest_prefix_offset >= prefix_replacements_size_) {
         ORTX_CXX_API_THROW("[UgmTok]Index out of array bounds in precompiled charsmap!", ORT_RUNTIME_EXCEPTION);
       }
+      // Validate that we have valid prefix_replacements_ data
+      if (prefix_replacements_ == nullptr || prefix_replacements_size_ == 0) {
+        ORTX_CXX_API_THROW("[UgmTok]prefix_replacements_ is null or empty!", ORT_RUNTIME_EXCEPTION);
+      }
       const char* prefix_replacement = &prefix_replacements_[longest_prefix_offset];
-      return {prefix_replacement, strlen(prefix_replacement), longest_prefix_length};
+      // Calculate safe length: find null terminator within remaining buffer
+      size_t max_len = prefix_replacements_size_ - longest_prefix_offset;
+      size_t replacement_len = 0;
+      while (replacement_len < max_len && prefix_replacement[replacement_len] != '\0') {
+        replacement_len++;
+      }
+      if (replacement_len == max_len) {
+        ORTX_CXX_API_THROW("[UgmTok]Replacement string not null-terminated in precompiled charsmap!", ORT_RUNTIME_EXCEPTION);
+      }
+      return {prefix_replacement, replacement_len, longest_prefix_length};
     } else {
       // if yes, return this sequence unmodified
       size_t prefix_offset = input_offset + ustring::UTF8Len(input[input_offset]);