The xor chain doesn't seem to have a huge effect on hash distribution.
The new version is so simple that gcc inlines it completely into the
callers, shrinks the binary size by half a kilobyte or so, and looks
marginally faster in synethetic tests.
$ x11perf -falseprecision -pointer
Before:
1000000 trep @ 0.0412 msec ( 24275.0/sec): QueryPointer
After:
1000000 trep @ 0.0374 msec ( 26737.0/sec): QueryPointer
Signed-off-by: Adam Jackson <a...@redhat.com>
---
dix/resource.c | 18 +-----------------
1 files changed, 1 insertions(+), 17 deletions(-)
diff --git a/dix/resource.c b/dix/resource.c
index 6bd2403..52519c9 100644
--- a/dix/resource.c
+++ b/dix/resource.c
@@ -335,23 +335,7 @@ InitClientResources(ClientPtr client)
static int
Hash(int client, XID id)
{
- id &= RESOURCE_ID_MASK;
- switch (clientTable[client].hashsize)
- {
- case 6:
- return ((int)(0x03F & (id ^ (id>>6) ^ (id>>12))));
- case 7:
- return ((int)(0x07F & (id ^ (id>>7) ^ (id>>13))));
- case 8:
- return ((int)(0x0FF & (id ^ (id>>8) ^ (id>>16))));
- case 9:
- return ((int)(0x1FF & (id ^ (id>>9))));
- case 10:
- return ((int)(0x3FF & (id ^ (id>>10))));
- case 11:
- return ((int)(0x7FF & (id ^ (id>>11))));
- }
- return -1;
+ return id & (clientTable[client].hashsize - 1);
}
static XID
--
1.7.3.4
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