Refactoring

cpp/devices/disk_cache.cpp

@@ -95,54 +95,40 @@ shared_ptr<DiskTrack> DiskCache::Assign(int track)
         }
     }
 
-    // Next, check for empty
-    for (size_t i = 0; i < cache.size(); ++i) {
-        if (!cache[i].disktrk) {
-            // Try loading
-            if (Load(static_cast<int>(i), track, nullptr)) {
-                // Success loading
-                cache[i].serial = serial;
-                return cache[i].disktrk;
-            }
-
-            // Load failed
-            return nullptr;
+    // Check for an empty cache slot
+    for (CacheData &c : cache) {
+        if (!c.disktrk && Load(&c - &cache[0], track, nullptr)) {
+            c.serial = serial;
+            return c.disktrk;
         }
     }
 
-    // Finally, find the youngest serial number and delete it
-
-    // Set index 0 as candidate c
+    // Find the cache entry with the smallest serial number, i.e. the oldest entry
     uint32_t s = cache[0].serial;
     size_t c = 0;
-
-    // Compare candidate with serial and update to smaller one
-    for (size_t i = 0; i < cache.size(); ++i) {
+    for (size_t i = 1; i < cache.size(); ++i) {
         assert(cache[i].disktrk);
 
-        // Compare and update the existing serial
         if (cache[i].serial < s) {
             s = cache[i].serial;
             c = i;
         }
     }
 
     // Save this track
-    if (!cache[c].disktrk->Save(sec_path, cache_miss_write_count)) {
-        return nullptr;
-    }
-
-    // Delete this track
-    shared_ptr<DiskTrack> disktrk = cache[c].disktrk;
-    cache[c].disktrk.reset();
-
-    if (Load(static_cast<int>(c), track, disktrk)) {
-        // Successful loading
-        cache[c].serial = serial;
-        return cache[c].disktrk;
+    if (cache[c].disktrk->Save(sec_path, cache_miss_write_count)) {
+        // Delete this track
+        shared_ptr<DiskTrack> disktrk = cache[c].disktrk;
+        cache[c].disktrk.reset();
+
+        if (Load(static_cast<int>(c), track, disktrk)) {
+            // Successful loading
+            cache[c].serial = serial;
+            return cache[c].disktrk;
+        }
     }
 
-    // Load failed
+    // Save or load failed
     return nullptr;
 }