[HB] Reuse the positions array as alt string array

src/hb-buffer-private.h

diff --git a/src/hb-buffer-private.h b/src/hb-buffer-private.h
index 948309d..f33f35f 100644
--- a/src/hb-buffer-private.h
+++ b/src/hb-buffer-private.h
@@ -78,7 +78,6 @@
 
   hb_internal_glyph_info_t     *in_string;
   hb_internal_glyph_info_t     *out_string;
-  hb_internal_glyph_info_t     *alt_string;
   hb_internal_glyph_position_t *positions;
 
   hb_direction_t       direction;

src/hb-buffer.c

diff --git a/src/hb-buffer.c b/src/hb-buffer.c
index fef3855..c197b90 100644
--- a/src/hb-buffer.c
+++ b/src/hb-buffer.c
@@ -46,11 +46,10 @@
  * in-place.
  *
  * As soon as out_string gets longer than in_string, out_string is moved over
- * to an alternate buffer (alt_string), and its current contents (out_length
- * entries) are copied to the alt buffer.  This should all remain transparent
- * to the user.  swap() then switches in_string and alt_string.  alt_string is
- * not allocated until its needed, but after that it's grown with in_string
- * unconditionally.
+ * to an alternate buffer (which we reuse the positions buffer for!), and its
+ * current contents (out_length entries) are copied to the alt buffer.
+ * This should all remain transparent to the user.  swap() then switches
+ * in_string and out_string.
  */
 
 /* XXX err handling */
@@ -63,10 +62,10 @@
   hb_buffer_ensure (buffer, size);
   if (buffer->out_string == buffer->in_string)
   {
-    if (!buffer->alt_string)
-      buffer->alt_string = calloc (buffer->allocated, sizeof (buffer->alt_string[0]));
+    if (!buffer->positions)
+      buffer->positions = calloc (buffer->allocated, sizeof (buffer->positions[0]));
 
-    buffer->out_string = buffer->alt_string;
+    buffer->out_string = buffer->positions;
     memcpy (buffer->out_string, buffer->in_string, buffer->out_length * sizeof (buffer->out_string[0]));
   }
 }
@@ -105,7 +104,6 @@
   HB_OBJECT_DO_DESTROY (buffer);
 
   free (buffer->in_string);
-  free (buffer->alt_string);
   free (buffer->positions);
 
   free (buffer);
@@ -138,19 +136,12 @@
     if (buffer->out_string != buffer->in_string)
     {
       buffer->in_string = realloc (buffer->in_string, new_allocated * sizeof (buffer->in_string[0]));
-      buffer->alt_string = realloc (buffer->alt_string, new_allocated * sizeof (buffer->alt_string[0]));
-      buffer->out_string = buffer->alt_string;
+      buffer->out_string = buffer->positions;
     }
     else
     {
       buffer->in_string = realloc (buffer->in_string, new_allocated * sizeof (buffer->in_string[0]));
       buffer->out_string = buffer->in_string;
-
-      if (buffer->alt_string)
-      {
-	free (buffer->alt_string);
-	buffer->alt_string = NULL;
-      }
     }
 
     buffer->allocated = new_allocated;
@@ -221,8 +212,7 @@
     hb_internal_glyph_info_t *tmp_string;
     tmp_string = buffer->in_string;
     buffer->in_string = buffer->out_string;
-    buffer->out_string = tmp_string;
-    buffer->alt_string = buffer->out_string;
+    buffer->positions = buffer->out_string = tmp_string;
   }
 
   tmp = buffer->in_length;