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Add inline murmurhash32(uint32) function.

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The function already existed in tidbitmap.c but more users requiring
fast hashing of 32bit ints are coming up.

Author: Andres Freund
Discussion: https://postgr.es/m/20170914061207.zxotvyopetm7lrrp@alap3.anarazel.de
This commit is contained in:
Andres Freund
2017-09-22 13:38:42 -07:00
parent 91ad8b416c
commit 791961f59b
2 changed files with 20 additions and 18 deletions
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20
src/backend/nodes/tidbitmap.c
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@@ -45,6 +45,7 @@
#include "nodes/tidbitmap.h"
#include "storage/lwlock.h"
#include "utils/dsa.h"
#include "utils/hashutils.h"
/*
* The maximum number of tuples per page is not large (typically 256 with
@@ -237,30 +238,13 @@ static int tbm_comparator(const void *left, const void *right);
static int tbm_shared_comparator(const void *left, const void *right,
void *arg);
/*
* Simple inline murmur hash implementation for the exact width required, for
* performance.
*/
static inline uint32
hash_blockno(BlockNumber b)
{
uint32 h = b;
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
h ^= h >> 16;
return h;
}
/* define hashtable mapping block numbers to PagetableEntry's */
#define SH_USE_NONDEFAULT_ALLOCATOR
#define SH_PREFIX pagetable
#define SH_ELEMENT_TYPE PagetableEntry
#define SH_KEY_TYPE BlockNumber
#define SH_KEY blockno
#define SH_HASH_KEY(tb, key) hash_blockno(key)
#define SH_HASH_KEY(tb, key) murmurhash32(key)
#define SH_EQUAL(tb, a, b) a == b
#define SH_SCOPE static inline
#define SH_DEFINE