From: Ben Pfaff <blp@gnu.org>
Date: Mon, 26 Jun 2006 05:37:53 +0000 (+0000)
Subject: Small optimization for hash library.
X-Git-Tag: sav-api~1815
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=04f575f9445589c64203a0204608a9751985ae68;p=pspp

Small optimization for hash library.
---

diff --git a/src/libpspp/ChangeLog b/src/libpspp/ChangeLog
index ec8a40de17..892dcd31aa 100644
--- a/src/libpspp/ChangeLog
+++ b/src/libpspp/ChangeLog
@@ -1,3 +1,13 @@
+Sun Jun 25 22:35:28 2006  Ben Pfaff  <blp@gnu.org>
+
+	Optimize rehashing: we know that none of the entries in the hash
+	table are equal, so we need not compare them to each other during
+	rehashing.
+	
+	* hash.c: (locate_empty_entry) New function.
+	(rehash) Use locate_empty_entry() instead of
+	locate_matching_entry().
+
 Fri Jun  9 14:03:29 2006  Ben Pfaff  <blp@gnu.org>
 
 	Reform string library.
diff --git a/src/libpspp/hash.c b/src/libpspp/hash.c
index 55b3a6f151..dcf8d8fffd 100644
--- a/src/libpspp/hash.c
+++ b/src/libpspp/hash.c
@@ -251,6 +251,24 @@ locate_matching_entry (struct hsh_table *h, const void *target)
     }
 }
 
+/* Returns the index of an empty entry that indicates
+   where TARGET should go, assuming that TARGET is not equal to
+   any item already in the hash table. */
+static inline unsigned
+locate_empty_entry (struct hsh_table *h, const void *target) 
+{
+  unsigned i = h->hash (target, h->aux);
+
+  assert (h->hash_ordered);
+  for (;;)
+    {
+      i &= h->size - 1;
+      if (h->entries[i] == NULL)
+	return i;
+      i--;
+    }
+}
+
 /* Changes the capacity of H to NEW_SIZE, which must be a
    positive power of 2 at least as large as the number of
    elements in H. */
@@ -277,7 +295,7 @@ rehash (struct hsh_table *h, size_t new_size)
     {
       void *entry = *table_p;
       if (entry != NULL)
-        h->entries[locate_matching_entry (h, entry)] = entry;
+        h->entries[locate_empty_entry (h, entry)] = entry;
     }
   free (begin);