hashmap: new and fast hashmap with dynamic size
ka-weihe
Alexander Medvednikov
parent
219239eadc
commit
6fd175d9be
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@ -2,113 +2,31 @@
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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module hashmap
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/*
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This is work in progress.
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A very early test version of the Hashmap with a fixed size.
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Only works with string keys and int values for now.
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I added this to improve performance of the V compiler,
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which uses lots of O(log n) map get's. Turned out with N < 10 000
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the performance gains are basically non-existent.
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*/
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struct Hashmap {
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cap int
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keys []string
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table []Hashmapentry
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elm_size int
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pub mut:
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nr_collisions int
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}
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struct Hashmapentry {
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mut:
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key string
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val int
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next &Hashmapentry // linked list for collisions
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}
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const (
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min_cap = 2<<10
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max_cap = 2<<20
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)
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const (
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initial_size = 2<<4
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initial_cap = initial_size - 1
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load_factor = 0.5
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probe_offset = u16(256)
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fnv64_prime = 1099511628211
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fnv64_offset_basis = 14695981039346656037
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)
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const(
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fnv32_offset_basis = u32(2166136261)
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fnv32_prime = u32(16777619)
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)
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pub fn new_hashmap(planned_nr_items int) Hashmap {
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mut cap := planned_nr_items * 5
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if cap < min_cap {
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cap = min_cap
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}
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if cap > max_cap {
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cap = max_cap
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}
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return Hashmap{
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cap: cap
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elm_size: 4
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table: make(cap, cap, sizeof(Hashmapentry))
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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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key_values &KeyValue
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cap int
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pub mut:
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size int
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}
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pub fn (m mut Hashmap) set(key string, val int) {
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// mut hash := int(b_fabs(key.hash()))
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// idx := hash % m.cap
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idx := int(fnv1a32(key) % m.cap)
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if m.table[idx].key.len != 0 {
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// println('\nset() idx=$idx key="$key" hash="$hash" val=$val')
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m.nr_collisions++
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// println('collision:' + m.table[idx].key)
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mut e := &m.table[idx]
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for e.next != 0 {
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e = e.next
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}
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e.next = &Hashmapentry{
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key,val,0}
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}
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else {
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m.table[idx] = Hashmapentry{
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key,val,0}
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}
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}
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pub fn (m &Hashmap) get(key string) int {
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// mut hash := int(b_fabs(key.hash()))
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// idx := hash % m.cap
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idx := int(fnv1a32(key) % m.cap)
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mut e := &m.table[idx]
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for e.next != 0 {
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// todo unsafe {
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if e.key == key {
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return e.val
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}
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e = e.next
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}
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return e.val
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}
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[inline]
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fn b_fabs(v int) f64 {
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return if v < 0 { -v } else { v }
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}
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// inline functions here for speed
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// rather than full impl in vlib
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[inline]
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fn fnv1a32(data string) u32 {
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mut hash := fnv32_offset_basis
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for i := 0; i < data.len; i++ {
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hash = (hash ^ u32(data[i])) * fnv32_prime
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}
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return hash
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struct KeyValue {
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key string
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mut:
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value int
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}
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[inline]
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@ -119,3 +37,207 @@ fn fnv1a64(data string) u64 {
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}
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return hash
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}
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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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size: 0
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}
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}
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pub fn (h mut Hashmap) set(key string, value int) {
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// The load factor is 0.5.
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// It will be adjustable in the future and with
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// a higher default settings to lower memory usage.
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if (h.size<<1) == (h.cap - 1) {
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h.rehash()
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}
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// Hash-function will be swapped for wyhash
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hash := fnv1a64(key)
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mut info := u16((hash>>56) | 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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index = (index + 1) & h.cap
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info += probe_offset
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}
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// While we might have a match
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for info == h.info[index] {
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if key == h.key_values[index].key {
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h.key_values[index].value = value
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return
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}
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index = (index + 1) & h.cap
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info += probe_offset
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}
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// Match is not possible anymore.
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// Probe until an empty index is found.
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// Swap when probe count is higher/richer (Robin Hood).
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mut current_key := key
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mut current_value := value
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for h.info[index] != 0 {
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if info > h.info[index] {
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tmp_kv := h.key_values[index]
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tmp_info := h.info[index]
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h.key_values[index] = KeyValue{
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current_key,current_value}
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h.info[index] = info
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current_key = tmp_kv.key
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current_value = tmp_kv.value
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info = tmp_info
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}
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index = (index + 1) & h.cap
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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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h.rehash()
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h.set(current_key, current_value)
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return
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}
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h.info[index] = info
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h.key_values[index] = KeyValue{
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current_key,current_value}
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h.size++
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}
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fn (h mut Hashmap) rehash() {
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old_cap := h.cap
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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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for i in 0 .. (old_cap + 1) {
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if h.info[i] != 0 {
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key := h.key_values[i].key
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value := h.key_values[i].value
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hash := fnv1a64(key)
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mut info := u16((hash>>56) | 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 < new_info[index] {
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index = (index + 1) & h.cap
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info += probe_offset
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}
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// While we might have a match
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for info == new_info[index] {
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if key == new_key_values[index].key {
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new_key_values[index].value = value
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return
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}
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index = (index + 1) & h.cap
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info += probe_offset
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}
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// Match is not possible anymore.
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// Probe until an empty index is found.
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// Swap when probe count is higher/richer (Robin Hood).
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mut current_key := key
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mut current_value := value
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for new_info[index] != 0 {
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if info > new_info[index] {
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tmp_kv := new_key_values[index]
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tmp_info := new_info[index]
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new_key_values[index] = KeyValue{
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current_key,current_value}
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new_info[index] = info
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current_key = tmp_kv.key
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current_value = tmp_kv.value
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info = tmp_info
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}
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index = (index + 1) & h.cap
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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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h.rehash()
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h.set(current_key, current_value)
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return
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}
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new_info[index] = info
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new_key_values[index] = KeyValue{
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current_key,current_value}
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}
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}
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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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pub fn (h mut Hashmap) delete(key string) {
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hash := fnv1a64(key)
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mut index := hash & h.cap
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mut info := u16((hash>>56) | 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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}
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// Perform backwards shifting
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for info == h.info[index] {
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if key == h.key_values[index].key {
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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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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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index = (index + 1) & h.cap
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current_info = h.info[index]
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}
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h.info[old_index] = 0
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h.size--
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return
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}
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index = (index + 1) & h.cap
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info += probe_offset
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}
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}
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pub fn (h Hashmap) get(key string) int {
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hash := fnv1a64(key)
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mut index := hash & h.cap
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mut info := u16((hash>>56) | 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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}
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for info == h.info[index] {
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if key == h.key_values[index].key {
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return h.key_values[index].value
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}
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index = (index + 1) & h.cap
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info += probe_offset
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}
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return 0
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}
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pub fn (h Hashmap) exists(key string) bool {
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hash := fnv1a64(key)
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mut index := hash & h.cap
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mut info := u16((hash>>56) | 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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}
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for info == h.info[index] {
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if key == h.key_values[index].key {
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return true
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}
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index = (index + 1) & h.cap
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info += probe_offset
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}
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return false
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}
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pub fn (h Hashmap) keys() []string {
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size := h.size
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mut keys := [''].repeat(size)
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mut j := 0
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for i in 0 .. (h.cap + 1) {
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if h.info[i] != 0 {
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keys[j] = h.key_values[i].key
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j++
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}
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}
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return keys
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}
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@ -3,7 +3,7 @@ module hashmap
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import rand
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fn test_random_strings() {
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mut m := new_hashmap(1000)
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mut m := new_hashmap()
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for i in 0..1000 {
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mut buf := []byte
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for j in 0..10 {
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@ -21,12 +21,11 @@ fn test_random_strings() {
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fn test_large_hashmap() {
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N := 300 * 1000
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mut nums := new_hashmap(N)
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mut nums := new_hashmap()
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for i := 0; i < N; i++ {
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key := i.str()
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nums.set(key, i)
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}
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println('nr collisions: $nums.nr_collisions')
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for i := 0; i < N; i++ {
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key := i.str()
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assert nums.get(key) == i
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