Fix: add a guard clause and change the type of _size in 3LCache (#251)

Enhancement: Change the type of _size from int32_t to uint64_t to support larger objects and cache sizes, preventing std::bad_array_new_length.

Author: ddkkpp

libCacheSim/cache/eviction/3LCache/ThreeLCache.cpp

@@ -307,10 +307,15 @@ void ThreeLCacheCache::evict() {
 }
 
 void ThreeLCacheCache::evict_with_candidate(pair<uint64_t, int32_t> &epair) {
+  int32_t old_pos = epair.second;
+  if (old_pos == -1) {
+    // No valid candidate to evict, avoid segfault
+    return;
+  }
+
   is_sampling = true;
   evict_nums -= 1;
   uint64_t key = epair.first;
-  int32_t old_pos = epair.second;
   _currentSize -= in_cache.metas[old_pos]._size;
 
   pred_map.erase(key);

libCacheSim/cache/eviction/3LCache/ThreeLCache.hpp

@@ -66,7 +66,7 @@ struct MetaExtra {
 class Meta {
  public:
   uint64_t _key;
-  int32_t _size;
+  uint64_t _size;
   uint64_t _past_timestamp;
   uint16_t _freq;
   MetaExtra *_extra = nullptr;