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annotate the hash functions

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This commit is contained in:
Chris Eagle 2016-12-18 19:45:09 -08:00
parent c7bd120650
commit 5690b7b68f
1 changed files with 14 additions and 2 deletions
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16
qemu/glib_compat.c
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@ -59,7 +59,12 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
/* hashing and equality functions */ /* hashing and equality functions */
/* too many pointers are multiples of 8/16 */ /*
Too many pointers are multiples of 8/16 so I rotate the low bits out
otherwise we get too many collisions at multiples of 8/16
This may be marginally better than what glib does in their direct_hash
but someone with some chops in this space should fix if it needs improving
*/
uint32_t g_direct_hash(const void *v) { uint32_t g_direct_hash(const void *v) {
#ifdef __HAVE_64_BIT_PTRS #ifdef __HAVE_64_BIT_PTRS
uint64_t hash = (uint64_t)v; uint64_t hash = (uint64_t)v;
@ -77,7 +82,10 @@ int g_direct_equal(const void *v1, const void *v2) {
return v1 == v2; return v1 == v2;
} }
/* djb2+ */ /*
djb2+ string hashing
see: http://www.cse.yorku.ca/~oz/hash.html
*/
uint32_t g_str_hash(const void *v) { uint32_t g_str_hash(const void *v) {
const char *s = (const char*)v; const char *s = (const char*)v;
uint32_t hash = 5381; uint32_t hash = 5381;
@ -92,6 +100,10 @@ int g_str_equal(const void *v1, const void *v2) {
return strcmp((const char*)v1, (const char*)v2) == 0; return strcmp((const char*)v1, (const char*)v2) == 0;
} }
/*
Bob Jenkins integer hash algorithm
see: http://burtleburtle.net/bob/hash/integer.html
*/
uint32_t g_int_hash(const void *v) { uint32_t g_int_hash(const void *v) {
uint32_t hash = *(const uint32_t*)v; uint32_t hash = *(const uint32_t*)v;
hash = (hash + 0x7ed55d16) + (hash << 12); hash = (hash + 0x7ed55d16) + (hash << 12);