[PATCH] [DbgHelp]: sparse array speed up

[Eric Pouech]

- implemented binary search (and other goodies) for
  sparse_array_lookup
- fixed type in spar(s)e_array_lookup name

On my local test bed for debug features, this merely gives
a 45% improvement for winedbg (actually dbghelp) when dealing with
dwarf debug information.
YMMV.

A+
---

 dlls/dbghelp/storage.c |   53 +++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/dlls/dbghelp/storage.c b/dlls/dbghelp/storage.c
index 3aee97d..9f72969 100644
--- a/dlls/dbghelp/storage.c
+++ b/dlls/dbghelp/storage.c
@@ -244,22 +244,55 @@ void sparse_array_init(struct sparse_arr
 }
 
 /******************************************************************
- *		spare_array_lookup
+ *		sparse_array_lookup
  *
  * Returns the first index which key is >= at passed key
  */
-static struct key2index* spare_array_lookup(const struct sparse_array* sa,
-                                            unsigned long key, unsigned* idx)
+static struct key2index* sparse_array_lookup(const struct sparse_array* sa,
+                                             unsigned long key, unsigned* idx)
 {
     struct key2index*   pk2i;
-
-    /* FIXME: should use bsearch here */
-    for (*idx = 0; *idx < sa->elements.num_elts; (*idx)++)
+    unsigned            low, high;
+    
+    if (!sa->elements.num_elts)
+    {
+        *idx = 0;
+        return NULL;
+    }
+    high = sa->elements.num_elts;
+    pk2i = vector_at(&sa->key2index, high - 1);
+    if (pk2i->key < key)
+    {
+        *idx = high;
+        return NULL;
+    }
+    if (pk2i->key == key)
+    {
+        *idx = high - 1;
+        return pk2i;
+    }
+    low = 0;
+    pk2i = vector_at(&sa->key2index, low);
+    if (pk2i->key >= key)
     {
+        *idx = 0;
+        return pk2i;
+    }
+    /* now we have: sa(lowest key) < key < sa(highest key) */
+    while (low < high)
+    {
+        *idx = (low + high) / 2;
         pk2i = vector_at(&sa->key2index, *idx);
-        if (pk2i && pk2i->key >= key) return pk2i;
+        if (pk2i->key > key)            high = *idx;
+        else if (pk2i->key < key)       low = *idx + 1;
+        else                            return pk2i;
     }
-    return NULL;
+    /* binary search could return exact item, we search for highest one
+     * below the key
+     */
+    if (pk2i->key < key)
+        pk2i = vector_at(&sa->key2index, ++(*idx));
+    return pk2i;
 }
 
 void*   sparse_array_find(const struct sparse_array* sa, unsigned long key)
@@ -267,7 +300,7 @@ void*   sparse_array_find(const struct s
     unsigned            idx;
     struct key2index*   pk2i;
 
-    if ((pk2i = spare_array_lookup(sa, key, &idx)) && pk2i->key == key)
+    if ((pk2i = sparse_array_lookup(sa, key, &idx)) && pk2i->key == key)
         return vector_at(&sa->elements, pk2i->index);
     return NULL;
 }
@@ -279,7 +312,7 @@ void*   sparse_array_add(struct sparse_a
     struct key2index*   pk2i;
     struct key2index*   to;
 
-    pk2i = spare_array_lookup(sa, key, &idx);
+    pk2i = sparse_array_lookup(sa, key, &idx);
     if (pk2i && pk2i->key == key)
     {
         FIXME("re adding an existing key\n");