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Store the hash value of a key in item_t in hb_map to reduce the number of hash computations.

This commit is contained in:
Garret Rieger 2019-10-22 11:55:04 -07:00
parent b33a0d628e
commit be5cdcdfa2
1 changed files with 40 additions and 30 deletions
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68
src/hb-map.hh
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@ -46,16 +46,13 @@ struct hb_hashmap_t
static_assert (hb_is_integral (K) || hb_is_pointer (K), "");
static_assert (hb_is_integral (V) || hb_is_pointer (V), "");
/* TODO If key type is a pointer, keep hash in item_t and use to:
* 1. avoid rehashing when resizing table, and
* 2. compare hash before comparing keys, for speed.
*/
struct item_t
{
K key;
V value;
uint32_t hash;
void clear () { key = kINVALID; value = vINVALID; }
void clear () { key = kINVALID; value = vINVALID; hash = 0; }
bool operator == (K o) { return hb_deref (key) == hb_deref (o); }
bool operator == (const item_t &o) { return *this == o.key; }
@ -137,7 +134,9 @@ struct hb_hashmap_t
if (old_items)
for (unsigned int i = 0; i < old_size; i++)
if (old_items[i].is_real ())
set (old_items[i].key, old_items[i].value);
set_with_hash (old_items[i].key,
old_items[i].hash,
old_items[i].value);
free (old_items);
@ -146,29 +145,9 @@ struct hb_hashmap_t
void set (K key, V value)
{
if (unlikely (!successful)) return;
if (unlikely (key == kINVALID)) return;
if ((occupancy + occupancy / 2) >= mask && !resize ()) return;
unsigned int i = bucket_for (key);
if (value == vINVALID && items[i].key != key)
return; /* Trying to delete non-existent key. */
if (!items[i].is_unused ())
{
occupancy--;
if (items[i].is_tombstone ())
population--;
set_with_hash (key, hb_hash (key), value);
}
items[i].key = key;
items[i].value = value;
occupancy++;
if (!items[i].is_tombstone ())
population++;
}
V get (K key) const
{
if (unlikely (!items)) return vINVALID;
@ -237,14 +216,45 @@ struct hb_hashmap_t
protected:
void set_with_hash (K key, uint32_t hash, V value)
{
if (unlikely (!successful)) return;
if (unlikely (key == kINVALID)) return;
if ((occupancy + occupancy / 2) >= mask && !resize ()) return;
unsigned int i = bucket_for_hash (key, hash);
if (value == vINVALID && items[i].key != key)
return; /* Trying to delete non-existent key. */
if (!items[i].is_unused ())
{
occupancy--;
if (items[i].is_tombstone ())
population--;
}
items[i].key = key;
items[i].value = value;
items[i].hash = hash;
occupancy++;
if (!items[i].is_tombstone ())
population++;
}
unsigned int bucket_for (K key) const
{
unsigned int i = hb_hash (key) % prime;
return bucket_for_hash (key, hb_hash (key));
}
unsigned int bucket_for_hash (K key, uint32_t hash) const
{
unsigned int i = hash % prime;
unsigned int step = 0;
unsigned int tombstone = (unsigned) -1;
while (!items[i].is_unused ())
{
if (items[i] == key)
if (items[i].hash == hash && items[i] == key)
return i;
if (tombstone == (unsigned) -1 && items[i].is_tombstone ())
tombstone = i;