mmap: Do not look for empty pool unless we need to

Given that we have a maximum of 12 pools, and much more
items to insert, it does not make sense to have two branches
in the hot path.

Move the search for an empty pool into the unlikely case
that no matching pool has been created yet - a condition
that is guaranteed to only happens up to 12 times.

1 files changed, 9 insertions, 8 deletions

diff --git a/apt-pkg/contrib/mmap.cc b/apt-pkg/contrib/mmap.cc
index ee6a21c83..020491172 100644
--- a/apt-pkg/contrib/mmap.cc
+++ b/apt-pkg/contrib/mmap.cc
@@ -357,25 +357,26 @@ unsigned long DynamicMMap::Allocate(unsigned long ItemSize)
 
    // Look for a matching pool entry
    Pool *I;
-   Pool *Empty = 0;
    for (I = Pools; I != Pools + PoolCount; ++I)
    {
-      if (I->ItemSize == 0)
-	 Empty = I;
       if (I->ItemSize == ItemSize)
 	 break;
    }
-   // No pool is allocated, use an unallocated one
-   if (I == Pools + PoolCount)
+   // No pool is allocated, use an unallocated one.
+   if (unlikely(I == Pools + PoolCount))
    {
+      for (I = Pools; I != Pools + PoolCount; ++I)
+      {
+	 if (I->ItemSize == 0)
+	    break;
+      }
       // Woops, we ran out, the calling code should allocate more.
-      if (Empty == 0)
+      if (I == Pools + PoolCount)
       {
 	 _error->Error("Ran out of allocation pools");
 	 return 0;
       }
-      
-      I = Empty;
+
       I->ItemSize = ItemSize;
       I->Count = 0;
    }