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