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atom: use a better hash function 

FNV-1a instead of the djb2-like one from before.

Keep the unrolling since it seems quite beneficial, even though it loses
one byte if the length is odd...

Signed-off-by: Ran Benita <ran@unusedvar.com>
master
Ran Benita 2019-11-09 12:43:04 +02:00
parent 9a92b4643b
commit ccab349c99
1 changed files with 15 additions and 5 deletions
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20
src/atom.c
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@ -73,6 +73,20 @@
#include "utils.h"
#include "atom.h"
/* FNV-1a (http://www.isthe.com/chongo/tech/comp/fnv/). */
static inline uint32_t
hash_buf(const char *string, size_t len)
{
uint32_t hash = 2166136261u;
for (size_t i = 0; i < len / 2; i++) {
hash ^= (uint8_t) string[i];
hash *= 0x01000193;
hash ^= (uint8_t) string[len - 1 - i];
hash *= 0x01000193;
}
return hash;
}
struct atom_node {
xkb_atom_t left, right;
uint32_t fingerprint;
@ -122,11 +136,7 @@ static bool
find_atom_pointer(struct atom_table *table, const char *string, size_t len,
xkb_atom_t **atomp_out, uint32_t *fingerprint_out)
{
uint32_t fingerprint = 0;
for (size_t i = 0; i < (len + 1) / 2; i++) {
fingerprint = fingerprint * 27 + string[i];
fingerprint = fingerprint * 27 + string[len - 1 - i];
}
uint32_t fingerprint = hash_buf(string, len);
xkb_atom_t *atomp = &table->root;
while (*atomp != XKB_ATOM_NONE) {