[Pspp-cvs] pspp/src/libpspp ChangeLog tower.c tower.h

[Ben Pfaff]

CVSROOT:        /cvsroot/pspp
Module name:    pspp
Changes by:     Ben Pfaff <blp> 07/06/04 01:29:08

Modified files:
        src/libpspp    : ChangeLog tower.c tower.h 

Log message:
        * tower.c: Cache repeated lookups of a single tower element.  This
        turns such lookups into O(1) operations without harming the big-O
        of other operations.
        
        * tower.h (struct tower): Add members for caching.

CVSWeb URLs:
http://cvs.savannah.gnu.org/viewcvs/pspp/src/libpspp/ChangeLog?cvsroot=pspp&r1=1.68&r2=1.69
http://cvs.savannah.gnu.org/viewcvs/pspp/src/libpspp/tower.c?cvsroot=pspp&r1=1.2&r2=1.3
http://cvs.savannah.gnu.org/viewcvs/pspp/src/libpspp/tower.h?cvsroot=pspp&r1=1.2&r2=1.3

Patches:
Index: ChangeLog
===================================================================
RCS file: /cvsroot/pspp/pspp/src/libpspp/ChangeLog,v
retrieving revision 1.68
retrieving revision 1.69
diff -u -b -r1.68 -r1.69
--- ChangeLog   4 Jun 2007 01:22:47 -0000       1.68
+++ ChangeLog   4 Jun 2007 01:29:08 -0000       1.69
@@ -1,5 +1,11 @@
 2007-06-03  Ben Pfaff  <address@hidden>
 
+       * tower.c: Cache repeated lookups of a single tower element.  This
+       turns such lookups into O(1) operations without harming the big-O
+       of other operations.
+
+       * tower.h (struct tower): Add members for caching.
+
        * range-set.c (range_set_clone): New function.
 
        * array.c (insert_range): New function.

Index: tower.c
===================================================================
RCS file: /cvsroot/pspp/pspp/src/libpspp/tower.c,v
retrieving revision 1.2
retrieving revision 1.3
diff -u -b -r1.2 -r1.3
--- tower.c     3 Apr 2007 22:55:07 -0000       1.2
+++ tower.c     4 Jun 2007 01:29:08 -0000       1.3
@@ -20,6 +20,8 @@
 
 #include <libpspp/tower.h>
 
+#include <limits.h>
+
 #include <libpspp/assertion.h>
 #include <libpspp/compiler.h>
 
@@ -38,6 +40,7 @@
 tower_init (struct tower *t) 
 {
   abt_init (&t->abt, NULL, reaugment_tower_node, NULL);
+  t->cache_bottom = ULONG_MAX;
 }
 
 /* Returns true if T contains no nodes, false otherwise. */
@@ -64,6 +67,7 @@
   new->height = height;
   abt_insert_before (&t->abt, under ? &under->abt_node : NULL,
                      &new->abt_node);
+  t->cache_bottom = ULONG_MAX;
 }
 
 /* Deletes NODE from tower T. */
@@ -72,6 +76,7 @@
 {
   struct tower_node *next = next_node (t, node);
   abt_delete (&t->abt, &node->abt_node);
+  t->cache_bottom = ULONG_MAX;
   return next;
 }
 
@@ -83,6 +88,7 @@
   assert (new_height > 0);
   node->height = new_height;
   abt_reaugmented (&t->abt, &node->abt_node);
+  t->cache_bottom = ULONG_MAX;
 }
 
 /* Removes nodes FIRST through LAST (exclusive) from tower SRC
@@ -110,6 +116,7 @@
       abt_insert_before (&dst->abt, under ? &under->abt_node : NULL,
                          &first->abt_node);
     }
+  dst->cache_bottom = src->cache_bottom = ULONG_MAX;
 }
 
 /* Returns the node at the given HEIGHT from the bottom of tower
@@ -118,14 +125,21 @@
    of the returned node, which may be less than HEIGHT if HEIGHT
    refers to the middle of a node instead of its bottom. */
 struct tower_node *
-tower_lookup (const struct tower *t,
+tower_lookup (const struct tower *t_,
               unsigned long height,
               unsigned long *node_start) 
 {
+  struct tower *t = (struct tower *) t_;
   struct abt_node *p;
 
   assert (height < tower_height (t));
 
+  if (height >= t->cache_bottom && height - t->cache_bottom < t->cache->height)
+    {
+      *node_start = t->cache_bottom;
+      return t->cache; 
+    }
+
   *node_start = 0;
   p = t->abt.root;
   for (;;)
@@ -147,6 +161,8 @@
           if (height < node_height) 
             {
               /* Our goal height is in P. */
+              t->cache = node;
+              t->cache_bottom = *node_start;
               return node; 
             }
           else 

Index: tower.h
===================================================================
RCS file: /cvsroot/pspp/pspp/src/libpspp/tower.h,v
retrieving revision 1.2
retrieving revision 1.3
diff -u -b -r1.2 -r1.3
--- tower.h     3 Apr 2007 22:55:07 -0000       1.2
+++ tower.h     4 Jun 2007 01:29:08 -0000       1.3
@@ -75,6 +75,8 @@
 struct tower 
   {
     struct abt abt;              /* Tree. */
+    struct tower_node *cache;         /* Cache node. */
+    unsigned long int cache_bottom;   /* Height of cache's bottom. */
   };
 
 void tower_init (struct tower *);