Attachment 82007 Details for Bug 66576 – [PATCH 1/2] Hash: clean up dead code and fix comments

[patch] [PATCH 1/2] Hash: clean up dead code and fix comments

0001-Hash-clean-up-dead-code-and-fix-comments.patch (text/plain), 3.44 KB, created by Chengwei Yang on 2013-07-04 08:04:30 UTC

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Creator: Chengwei Yang

Created: 2013-07-04 08:04:30 UTC

Size: 3.44 KB

patch

obsolete

>From c0bb9790bd00a076c405f3eefe6c052427d8bac1 Mon Sep 17 00:00:00 2001
>From: Chengwei Yang <chengwei.yang@intel.com>
>Date: Thu, 4 Jul 2013 15:59:38 +0800
>Subject: [PATCH 1/2] Hash: clean up dead code and fix comments
>
>Signed-off-by: Chengwei Yang <chengwei.yang@intel.com>
>---
> dbus/dbus-hash.c |   43 +++++++++++++++++--------------------------
> 1 file changed, 17 insertions(+), 26 deletions(-)
>
>diff --git a/dbus/dbus-hash.c b/dbus/dbus-hash.c
>index c80835a..f75bcc0 100644
>--- a/dbus/dbus-hash.c
>+++ b/dbus/dbus-hash.c
>@@ -110,14 +110,27 @@
>  * different buckets.  The hash function was taken from a
>  * random-number generator. (This is used to hash integers.)
>  *
>- * The down_shift drops off the high bits of the hash index, and
>+ * The down_shift drops off the low bits of the hash index, and
>  * decreases as we increase the number of hash buckets (to keep more
>  * range in the hash index). The mask also strips high bits and strips
>  * fewer high bits as the number of hash buckets increases.
>- * I don't understand two things: why is the initial downshift 28
>+ *
>+ * Q: I don't understand two things: why is the initial down_shift 28
>  * to keep 4 bits when the initial mask is 011 to keep 2 bits,
>  * and why do we have both a mask and a downshift?
>- * 
>+ *
>+ * A: In fact, we can merge down_shift and mask into one MASK, like
>+ * at init: MASK = (0x3 << 28)
>+ * at growing: MASK += (0x3 << 26)
>+ * at shrinking: MASK -= (0x3 << 26)
>+ * As the above example, it's ugly and confusing, also need another
>+ * field to place the role as how many bits should we shift to left,
>+ * that is the down_shift(may be up_shift) in fact.
>+ *
>+ * The answer to why down_shift init to 28 while mask to 3. Thinking
>+ * again that we're creating hash table, so we *need* some chances to
>+ * conflicts. So the highest *2* bits are left to do so, just as an
>+ * granularity, in theoritical it can be any other value.
>  */
> #define RANDOM_INDEX(table, i) \
>     (((((intptr_t) (i))*1103515245) >> (table)->down_shift) & (table)->mask)
>@@ -364,25 +377,6 @@ _dbus_hash_table_unref (DBusHashTable *table)
> 
>   if (table->refcount == 0)
>     {
>-#if 0
>-      DBusHashEntry *entry;
>-      DBusHashEntry *next;
>-      int i;
>-
>-      /* Free the entries in the table. */
>-      for (i = 0; i < table->n_buckets; i++)
>-        {
>-          entry = table->buckets[i];
>-          while (entry != NULL)
>-            {
>-              next = entry->next;
>-
>-              free_entry (table, entry);
>-              
>-              entry = next;
>-            }
>-        }
>-#else
>       DBusHashEntry *entry;
>       int i;
> 
>@@ -399,7 +393,6 @@ _dbus_hash_table_unref (DBusHashTable *table)
>         }
>       /* We can do this very quickly with memory pools ;-) */
>       _dbus_mem_pool_free (table->entry_pool);
>-#endif
>       
>       /* Free the bucket array, if it was dynamically allocated. */
>       if (table->buckets != table->static_buckets)
>@@ -982,14 +975,12 @@ rebuild_table (DBusHashTable *table)
>       table->mask = table->mask >> 2; /* keep 2 fewer high bits */
>     }
> 
>-#if 0
>-  printf ("%s table to lo = %d hi = %d downshift = %d mask = 0x%x\n",
>+  _dbus_verbose ("%s table to lo = %d hi = %d downshift = %d mask = 0x%x\n",
>           growing ? "GROW" : "SHRINK",
>           table->lo_rebuild_size,
>           table->hi_rebuild_size,
>           table->down_shift,
>           table->mask);
>-#endif
>   
>   _dbus_assert (table->lo_rebuild_size >= 0);
>   _dbus_assert (table->hi_rebuild_size > table->lo_rebuild_size);
>-- 
>1.7.9.5
>

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