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hashmap: optimization of rehashing

pull/3615/head
ka-weihe 2020-01-31 02:29:35 +01:00 committed by GitHub
parent 80d936adc1
commit 23dd6e2294
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 49 additions and 20 deletions
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69
vlib/builtin/hashmap/hashmap.v
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@ -6,17 +6,24 @@ module hashmap
import hash.wyhash import hash.wyhash
const ( const (
initial_size = 2 << 4 log_size = 5
n_hashbits = 24
window_size = 16
initial_size = 1 << log_size
initial_cap = initial_size - 1 initial_cap = initial_size - 1
probe_offset = u16(256) default_load_factor = 0.8
load_factor = 0.8 hashbit_mask = u32(0xFFFFFF)
probe_offset = u32(0x1000000)
max_probe = u32(0xFF000000)
) )
pub struct Hashmap { pub struct Hashmap {
mut: mut:
info &u16 cap u32
shift byte
window byte
info &u32
key_values &KeyValue key_values &KeyValue
cap int
pub mut: pub mut:
load_factor f32 load_factor f32
size int size int
@ -30,10 +37,12 @@ mut:
pub fn new_hashmap() Hashmap { pub fn new_hashmap() Hashmap {
return Hashmap{ return Hashmap{
info: &u16(calloc(sizeof(u16) * initial_size))
key_values: &KeyValue(calloc(sizeof(KeyValue) * initial_size))
cap: initial_cap cap: initial_cap
load_factor: 0.8 shift: log_size
window: window_size
info: &u32(calloc(sizeof(u32) * initial_size))
key_values: &KeyValue(calloc(sizeof(KeyValue) * initial_size))
load_factor: default_load_factor
size: 0 size: 0
} }
} }
@ -44,7 +53,7 @@ pub fn (h mut Hashmap) set(key string, value int) {
h.rehash() h.rehash()
} }
hash := wyhash.wyhash_c(key.str, u64(key.len), 0) hash := wyhash.wyhash_c(key.str, u64(key.len), 0)
mut info := u16((hash >> 56) | probe_offset) mut info := u32(((hash >> h.shift) & hashbit_mask) | probe_offset)
mut index := hash & h.cap mut index := hash & h.cap
// While probe count is less // While probe count is less
for info < h.info[index] { for info < h.info[index] {
@ -71,7 +80,7 @@ pub fn (h mut Hashmap) set(key string, value int) {
h.info[index] = info h.info[index] = info
info = tmp_info info = tmp_info
// Swap KeyValue // Swap KeyValue
tmp_kv := h.key_values[index] tmp_kv := h.key_values[index]
h.key_values[index] = current_kv h.key_values[index] = current_kv
current_kv = tmp_kv current_kv = tmp_kv
} }
@ -79,7 +88,7 @@ pub fn (h mut Hashmap) set(key string, value int) {
info += probe_offset info += probe_offset
} }
// Should almost never happen // Should almost never happen
if (info & 0xFF00) == 0xFF00 { if (info & max_probe) == max_probe {
h.rehash() h.rehash()
h.set(current_kv.key, current_kv.value) h.set(current_kv.key, current_kv.value)
return return
@ -91,14 +100,29 @@ pub fn (h mut Hashmap) set(key string, value int) {
fn (h mut Hashmap) rehash() { fn (h mut Hashmap) rehash() {
old_cap := h.cap old_cap := h.cap
h.window--
// check if any hashbits are left
if h.window == 0 {
h.shift += window_size
}
// double the size of the hashmap
h.cap = ((h.cap + 1) << 1) - 1 h.cap = ((h.cap + 1) << 1) - 1
mut new_key_values := &KeyValue(calloc(sizeof(KeyValue) * (h.cap + 1))) mut new_key_values := &KeyValue(calloc(sizeof(KeyValue) * (h.cap + 1)))
mut new_info := &u16(calloc(sizeof(u16) * (h.cap + 1))) mut new_info := &u32(calloc(sizeof(u32) * (h.cap + 1)))
for i in 0 .. (old_cap + 1) { for i in 0 .. (old_cap + 1) {
if h.info[i] != 0 { if h.info[i] != 0 {
mut kv := h.key_values[i] mut kv := h.key_values[i]
hash := wyhash.wyhash_c(kv.key.str, u64(kv.key.len), 0) mut hash := u64(0)
mut info := u16((hash >> 56) | probe_offset) mut info := u32(0)
if h.window == 0 {
hash = wyhash.wyhash_c(kv.key.str, u64(kv.key.len), 0)
info = u32(((hash >> h.shift) & hashbit_mask) | probe_offset)
}
else {
original := u64(i - ((h.info[i] >> n_hashbits) - 1)) & (h.cap >> 1)
hash = original | (h.info[i] << h.shift)
info = (h.info[i] & hashbit_mask) | probe_offset
}
mut index := hash & h.cap mut index := hash & h.cap
// While probe count is less // While probe count is less
for info < new_info[index] { for info < new_info[index] {
@ -114,7 +138,7 @@ fn (h mut Hashmap) rehash() {
new_info[index] = info new_info[index] = info
info = tmp_info info = tmp_info
// Swap KeyValue // Swap KeyValue
tmp_kv := new_key_values[index] tmp_kv := new_key_values[index]
new_key_values[index] = kv new_key_values[index] = kv
kv = tmp_kv kv = tmp_kv
} }
@ -122,7 +146,7 @@ fn (h mut Hashmap) rehash() {
info += probe_offset info += probe_offset
} }
// Should almost never happen // Should almost never happen
if (info & 0xFF00) == 0xFF00 { if (info & max_probe) == max_probe {
h.rehash() h.rehash()
h.set(kv.key, kv.value) h.set(kv.key, kv.value)
return return
@ -131,6 +155,11 @@ fn (h mut Hashmap) rehash() {
new_key_values[index] = kv new_key_values[index] = kv
} }
} }
if h.window == 0 {
h.window = window_size
}
free(h.key_values)
free(h.info)
h.key_values = new_key_values h.key_values = new_key_values
h.info = new_info h.info = new_info
} }
@ -138,7 +167,7 @@ fn (h mut Hashmap) rehash() {
pub fn (h mut Hashmap) delete(key string) { pub fn (h mut Hashmap) delete(key string) {
hash := wyhash.wyhash_c(key.str, u64(key.len), 0) hash := wyhash.wyhash_c(key.str, u64(key.len), 0)
mut index := hash & h.cap mut index := hash & h.cap
mut info := u16((hash >> 56) | probe_offset) mut info := u32(((hash >> h.shift) & hashbit_mask) | probe_offset)
for info < h.info[index] { for info < h.info[index] {
index = (index + 1) & h.cap index = (index + 1) & h.cap
info += probe_offset info += probe_offset
@ -149,7 +178,7 @@ pub fn (h mut Hashmap) delete(key string) {
mut old_index := index mut old_index := index
index = (index + 1) & h.cap index = (index + 1) & h.cap
mut current_info := h.info[index] mut current_info := h.info[index]
for (current_info >> 8) > 1 { for (current_info >> n_hashbits) > 1 {
h.info[old_index] = current_info - probe_offset h.info[old_index] = current_info - probe_offset
h.key_values[old_index] = h.key_values[index] h.key_values[old_index] = h.key_values[index]
old_index = index old_index = index
@ -168,7 +197,7 @@ pub fn (h mut Hashmap) delete(key string) {
pub fn (h Hashmap) get(key string) int { pub fn (h Hashmap) get(key string) int {
hash := wyhash.wyhash_c(key.str, u64(key.len), 0) hash := wyhash.wyhash_c(key.str, u64(key.len), 0)
mut index := hash & h.cap mut index := hash & h.cap
mut info := u16((hash >> 56) | probe_offset) mut info := u32(((hash >> h.shift) & hashbit_mask) | probe_offset)
for info < h.info[index] { for info < h.info[index] {
index = (index + 1) & h.cap index = (index + 1) & h.cap
info += probe_offset info += probe_offset
@ -186,7 +215,7 @@ pub fn (h Hashmap) get(key string) int {
pub fn (h Hashmap) exists(key string) bool { pub fn (h Hashmap) exists(key string) bool {
hash := wyhash.wyhash_c(key.str, u64(key.len), 0) hash := wyhash.wyhash_c(key.str, u64(key.len), 0)
mut index := hash & h.cap mut index := hash & h.cap
mut info := u16((hash >> 56) | probe_offset) mut info := u32(((hash >> h.shift) & hashbit_mask) | probe_offset)
for info < h.info[index] { for info < h.info[index] {
index = (index + 1) & h.cap index = (index + 1) & h.cap
info += probe_offset info += probe_offset