Changeset: a2d5c738541a for MonetDB
URL: http://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=a2d5c738541a
Modified Files:
gdk/gdk_group.c
Branch: Feb2013
Log Message:
simplified bit-shifting for subgrouping / compound-key checking
diffs (46 lines):
diff --git a/gdk/gdk_group.c b/gdk/gdk_group.c
--- a/gdk/gdk_group.c
+++ b/gdk/gdk_group.c
@@ -76,8 +76,7 @@
if (grps) { \
BUN hv = hash_##TYPE(hs, v); \
BUN hg = hash_oid(hs, &grps[p-r]); \
- prb = (hv ^ (hv << bits1) ^ \
- hg ^ (hg << bits2)) & hs->mask; \
+ prb = ((hv << bits) ^ hg) & hs->mask; \
for (hb = hs->hash[prb]; \
hb != BUN_NONE; \
hb = hs->link[hb]) { \
@@ -489,17 +488,15 @@ BATgroup_internal(BAT **groups, BAT **ex
Heap *hp = NULL;
BUN prb;
BUN mask = HASHmask(b->batCount) >> 3;
- int bits1 = 3, bits2;
+ int bits = 3;
/* when combining value and group-id hashes,
- * left-shift them by, respectively,
- * 1/3 & 2/3 of the hash-mask width
- * to better spread bits and use entire hash-mask,
+ * we left-shift one of them by half the hash-mask width
+ * to better spread bits and use the entire hash-mask,
* and thus reduce collisions */
while (mask>>=1)
- bits1++;
- bits1 /= 3;
- bits2 = 2 * bits1;
+ bits++;
+ bits /= 2;
/* not sorted, and no pre-existing hash table: we'll
* build an incomplete hash table on the fly--also see
@@ -562,8 +559,7 @@ BATgroup_internal(BAT **groups, BAT **ex
if (grps) {
BUN hv = hash_any(hs, v);
BUN hg = hash_oid(hs, &grps[p-r]);
- prb = (hv ^ (hv << bits1) ^
- hg ^ (hg << bits2)) & hs->mask;
+ prb = ((hv << bits) ^ hg) & hs->mask;
for (hb = hs->hash[prb];
hb != BUN_NONE;
hb = hs->link[hb]) {
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