443 lines
12 KiB
V
443 lines
12 KiB
V
// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
|
|
// Use of this source code is governed by an MIT license
|
|
// that can be found in the LICENSE file.
|
|
module builtin
|
|
|
|
import strings
|
|
import hash.wyhash
|
|
|
|
fn C.memcmp(byteptr, byteptr, int) int
|
|
|
|
/*
|
|
This is a highly optimized hashmap implementation. It has several traits that
|
|
in combination makes it very fast and memory efficient. Here is a short expl-
|
|
anation of each trait. After reading this you should have a basic understand-
|
|
ing of how it functions:
|
|
|
|
1. Hash-function: Wyhash. Wyhash is the fastest hash-function for short keys
|
|
passing SMHasher, so it was an obvious choice.
|
|
|
|
2. Open addressing: Robin Hood Hashing. With this method, a hash-collision is
|
|
resolved by probing. As opposed to linear probing, Robin Hood hashing has a
|
|
simple but clever twist: As new keys are inserted, old keys are shifted arou-
|
|
nd in a way such that all keys stay reasonably close to the slot they origin-
|
|
ally hash to. A new key may displace a key already inserted if its probe cou-
|
|
nt is larger than that of the key at the current position.
|
|
|
|
3. Memory layout: key-value pairs are stored in a `DenseArray`. This is a dy-
|
|
namic array with a very low volume of unused memory, at the cost of more rea-
|
|
llocations when inserting elements. It also preserves the order of the key-v-
|
|
alues. This array is named `key_values`. Instead of probing a new key-value,
|
|
this map probes two 32-bit numbers collectively. The first number has its 8
|
|
most significant bits reserved for the probe-count and the remaining 24 bits
|
|
are cached bits from the hash which are utilized for faster re-hashing. This
|
|
number is often referred to as `meta`. The other 32-bit number is the index
|
|
at which the key-value was pushed to in `key_values`. Both of these numbers
|
|
are stored in a sparse array `metas`. The `meta`s and `kv_index`s are stored
|
|
at even and odd indices, respectively:
|
|
|
|
metas = [meta, kv_index, 0, 0, meta, kv_index, 0, 0, meta, kv_index, ...]
|
|
key_values = [kv, kv, kv, ...]
|
|
|
|
4. The size of metas is a power of two. This enables the use of bitwise AND
|
|
to convert the 64-bit hash to a bucket/index that doesn't overflow metas. If
|
|
the size is power of two you can use "hash & (SIZE - 1)" instead of "hash %
|
|
SIZE". Modulo is extremely expensive so using '&' is a big performance impro-
|
|
vement. The general concern with this approach is that you only make use of
|
|
the lower bits of the hash which can cause more collisions. This is solved by
|
|
using a well-dispersed hash-function.
|
|
|
|
5. The hashmap keeps track of the highest probe_count. The trick is to alloc-
|
|
ate `extra_metas` > max(probe_count), so you never have to do any bounds-che-
|
|
cking since the extra meta memory ensures that a meta will never go beyond
|
|
the last index.
|
|
|
|
6. Cached rehashing. When the `load_factor` of the map exceeds the `max_load_
|
|
factor` the size of metas is doubled and all the key-values are "rehashed" to
|
|
find the index for their meta's in the new array. Instead of rehashing compl-
|
|
etely, it simply uses the cached-hashbits stored in the meta, resulting in
|
|
much faster rehashing.
|
|
*/
|
|
|
|
const (
|
|
// Number of bits from the hash stored for each entry
|
|
hashbits = 24
|
|
// Number of bits from the hash stored for rehashing
|
|
max_cached_hashbits = 16
|
|
// Initial log-number of buckets in the hashtable
|
|
init_log_capicity = 5
|
|
// Initial number of buckets in the hashtable
|
|
init_capicity = 1<<init_log_capicity
|
|
// Maximum load-factor (size / capacity)
|
|
max_load_factor = 0.8
|
|
// Initial highest even index in metas
|
|
init_cap = init_capicity - 2
|
|
// Used for incrementing `extra_metas` when max
|
|
// probe count is too high, to avoid overflow
|
|
extra_metas_inc = 4
|
|
// Bitmask to select all the hashbits
|
|
hash_mask = u32(0x00FFFFFF)
|
|
// Used for incrementing the probe-count
|
|
probe_inc = u32(0x01000000)
|
|
)
|
|
|
|
// This function is intended to be fast when
|
|
// the strings are very likely to be equal
|
|
// TODO: add branch prediction hints
|
|
[inline]
|
|
fn fast_string_eq(a, b string) bool {
|
|
if a.len != b.len {
|
|
return false
|
|
}
|
|
return C.memcmp(a.str, b.str, b.len) == 0
|
|
}
|
|
|
|
struct KeyValue {
|
|
key string
|
|
mut:
|
|
value voidptr
|
|
}
|
|
|
|
// Dynamic array with very low growth factor
|
|
struct DenseArray {
|
|
mut:
|
|
cap u32
|
|
size u32
|
|
deletes u32
|
|
data &KeyValue
|
|
}
|
|
|
|
[inline]
|
|
fn new_dense_array() DenseArray {
|
|
unsafe{
|
|
return DenseArray{
|
|
cap: 8
|
|
size: 0
|
|
deletes: 0
|
|
data: &KeyValue(malloc(8 * sizeof(KeyValue)))
|
|
}
|
|
}
|
|
}
|
|
|
|
// Push element to array and return index
|
|
// The growth-factor is roughly 1.125 `(x + (x >> 3))`
|
|
[inline]
|
|
fn (d mut DenseArray) push(kv KeyValue) u32 {
|
|
if d.cap == d.size {
|
|
d.cap += d.cap>>3
|
|
d.data = &KeyValue(C.realloc(d.data, sizeof(KeyValue) * d.cap))
|
|
}
|
|
push_index := d.size
|
|
d.data[push_index] = kv
|
|
d.size++
|
|
return push_index
|
|
}
|
|
|
|
// Private function. Used to implement array[] operator
|
|
fn (d DenseArray) get(i int) voidptr {
|
|
$if !no_bounds_checking? {
|
|
if i < 0 || i >= d.size {
|
|
panic('DenseArray.get: index out of range (i == $i, d.len == $d.size)')
|
|
}
|
|
}
|
|
return byteptr(d.data) + i * sizeof(KeyValue)
|
|
}
|
|
|
|
// Move all zeros to the end of the array
|
|
// and resize array
|
|
fn (d mut DenseArray) zeros_to_end() {
|
|
mut count := u32(0)
|
|
for i in 0 .. d.size {
|
|
if d.data[i].key.str != 0 {
|
|
tmp := d.data[count]
|
|
d.data[count] = d.data[i]
|
|
d.data[i] = tmp
|
|
count++
|
|
}
|
|
}
|
|
d.deletes = 0
|
|
d.size = count
|
|
d.cap = if count < 8 { u32(8) } else { count }
|
|
d.data = &KeyValue(C.realloc(d.data, sizeof(KeyValue) * d.cap))
|
|
}
|
|
|
|
pub struct map {
|
|
// Byte size of value
|
|
value_bytes int
|
|
mut:
|
|
// highest even index in the hashtable
|
|
cap u32
|
|
// Number of cached hashbits left for rehasing
|
|
cached_hashbits byte
|
|
// Used for right-shifting out used hashbits
|
|
shift byte
|
|
// Array storing key-values (ordered)
|
|
key_values DenseArray
|
|
// Pointer to meta-data:
|
|
// Odd indices store kv_index.
|
|
// Even indices store probe_count and hashbits.
|
|
metas &u32
|
|
// Extra metas that allows for no ranging when incrementing
|
|
// index in the hashmap
|
|
extra_metas u32
|
|
pub mut:
|
|
// Number of key-values currently in the hashmap
|
|
size int
|
|
}
|
|
|
|
// TODO: remove this after vc is regenerated.
|
|
fn new_map(n, value_bytes int) map {
|
|
return new_map_1(value_bytes)
|
|
}
|
|
fn new_map_1(value_bytes int) map {
|
|
return map{
|
|
value_bytes: value_bytes
|
|
cap: init_cap
|
|
cached_hashbits: max_cached_hashbits
|
|
shift: init_log_capicity
|
|
key_values: new_dense_array()
|
|
metas: &u32(vcalloc(sizeof(u32) * (init_capicity + extra_metas_inc)))
|
|
extra_metas: extra_metas_inc
|
|
size: 0
|
|
}
|
|
}
|
|
|
|
fn new_map_init(n, value_bytes int, keys &string, values voidptr) map {
|
|
mut out := new_map_1(value_bytes)
|
|
for i in 0 .. n {
|
|
out.set(keys[i], byteptr(values) + i * value_bytes)
|
|
}
|
|
return out
|
|
}
|
|
|
|
[inline]
|
|
fn (m &map) key_to_index(key string) (u32,u32) {
|
|
hash := wyhash.wyhash_c(key.str, u64(key.len), 0)
|
|
index := hash & m.cap
|
|
meta := ((hash>>m.shift) & hash_mask) | probe_inc
|
|
return u32(index),u32(meta)
|
|
}
|
|
|
|
[inline]
|
|
fn (m &map) meta_less(_index u32, _metas u32) (u32,u32) {
|
|
mut index := _index
|
|
mut meta := _metas
|
|
for meta < m.metas[index] {
|
|
index += 2
|
|
meta += probe_inc
|
|
}
|
|
return index,meta
|
|
}
|
|
|
|
[inline]
|
|
fn (m mut map) meta_greater(_index u32, _metas u32, kvi u32) {
|
|
mut meta := _metas
|
|
mut index := _index
|
|
mut kv_index := kvi
|
|
for m.metas[index] != 0 {
|
|
if meta > m.metas[index] {
|
|
tmp_meta := m.metas[index]
|
|
m.metas[index] = meta
|
|
meta = tmp_meta
|
|
tmp_index := m.metas[index + 1]
|
|
m.metas[index + 1] = kv_index
|
|
kv_index = tmp_index
|
|
}
|
|
index += 2
|
|
meta += probe_inc
|
|
}
|
|
m.metas[index] = meta
|
|
m.metas[index + 1] = kv_index
|
|
probe_count := (meta>>hashbits) - 1
|
|
if (probe_count<<1) == m.extra_metas {
|
|
m.extra_metas += extra_metas_inc
|
|
mem_size := (m.cap + 2 + m.extra_metas)
|
|
m.metas = &u32(C.realloc(m.metas, sizeof(u32) * mem_size))
|
|
C.memset(m.metas + mem_size - extra_metas_inc, 0, sizeof(u32) * extra_metas_inc)
|
|
// Should almost never happen
|
|
if probe_count == 252 {
|
|
panic('Probe overflow')
|
|
}
|
|
}
|
|
}
|
|
|
|
fn (m mut map) set(key string, value voidptr) {
|
|
load_factor := f32(m.size<<1) / f32(m.cap)
|
|
if load_factor > max_load_factor {
|
|
m.expand()
|
|
}
|
|
mut index,mut meta := m.key_to_index(key)
|
|
index,meta = m.meta_less(index, meta)
|
|
// While we might have a match
|
|
for meta == m.metas[index] {
|
|
kv_index := m.metas[index + 1]
|
|
if fast_string_eq(key, m.key_values.data[kv_index].key) {
|
|
C.memcpy(m.key_values.data[kv_index].value, value, m.value_bytes)
|
|
return
|
|
}
|
|
index += 2
|
|
meta += probe_inc
|
|
}
|
|
// Match not possible anymore
|
|
kv := KeyValue{
|
|
key: key
|
|
value: malloc(m.value_bytes)
|
|
}
|
|
C.memcpy(kv.value, value, m.value_bytes)
|
|
kv_index := m.key_values.push(kv)
|
|
m.meta_greater(index, meta, kv_index)
|
|
m.size++
|
|
}
|
|
|
|
// Doubles the size of the hashmap
|
|
fn (m mut map) expand() {
|
|
old_cap := m.cap
|
|
m.cap = ((m.cap + 2)<<1) - 2
|
|
// Check if any hashbits are left
|
|
if m.cached_hashbits == 0 {
|
|
m.shift += max_cached_hashbits
|
|
m.cached_hashbits = max_cached_hashbits
|
|
m.rehash()
|
|
}
|
|
else {
|
|
m.cached_rehash(old_cap)
|
|
}
|
|
m.cached_hashbits--
|
|
}
|
|
|
|
fn (m mut map) rehash() {
|
|
meta_bytes := sizeof(u32) * (m.cap + 2 + m.extra_metas)
|
|
m.metas = &u32(C.realloc(m.metas, meta_bytes))
|
|
C.memset(m.metas, 0, meta_bytes)
|
|
for i := u32(0); i < m.key_values.size; i++ {
|
|
if m.key_values.data[i].key.str == 0 {
|
|
continue
|
|
}
|
|
kv := m.key_values.data[i]
|
|
mut index,mut meta := m.key_to_index(kv.key)
|
|
index,meta = m.meta_less(index, meta)
|
|
m.meta_greater(index, meta, i)
|
|
}
|
|
}
|
|
|
|
fn (m mut map) cached_rehash(old_cap u32) {
|
|
old_metas := m.metas
|
|
m.metas = &u32(vcalloc(sizeof(u32) * (m.cap + 2 + m.extra_metas)))
|
|
old_extra_metas := m.extra_metas
|
|
for i := u32(0); i <= old_cap + old_extra_metas; i += 2 {
|
|
if old_metas[i] == 0 {
|
|
continue
|
|
}
|
|
old_meta := old_metas[i]
|
|
old_probe_count := ((old_meta>>hashbits) - 1)<<1
|
|
old_index := (i - old_probe_count) & (m.cap>>1)
|
|
mut index := (old_index | (old_meta<<m.shift)) & m.cap
|
|
mut meta := (old_meta & hash_mask) | probe_inc
|
|
index,meta = m.meta_less(index, meta)
|
|
kv_index := old_metas[i + 1]
|
|
m.meta_greater(index, meta, kv_index)
|
|
}
|
|
unsafe{
|
|
free(old_metas)
|
|
}
|
|
}
|
|
|
|
fn (m map) get3(key string, zero voidptr) voidptr {
|
|
mut index,mut meta := m.key_to_index(key)
|
|
index,meta = m.meta_less(index, meta)
|
|
for meta == m.metas[index] {
|
|
kv_index := m.metas[index + 1]
|
|
if fast_string_eq(key, m.key_values.data[kv_index].key) {
|
|
return m.key_values.data[kv_index].value
|
|
}
|
|
index += 2
|
|
meta += probe_inc
|
|
}
|
|
return zero
|
|
}
|
|
|
|
fn (m map) exists(key string) bool {
|
|
mut index,mut meta := m.key_to_index(key)
|
|
index,meta = m.meta_less(index, meta)
|
|
for meta == m.metas[index] {
|
|
kv_index := m.metas[index + 1]
|
|
if fast_string_eq(key, m.key_values.data[kv_index].key) {
|
|
return true
|
|
}
|
|
index += 2
|
|
meta += probe_inc
|
|
}
|
|
return false
|
|
}
|
|
|
|
pub fn (m mut map) delete(key string) {
|
|
mut index,mut meta := m.key_to_index(key)
|
|
index,meta = m.meta_less(index, meta)
|
|
// Perform backwards shifting
|
|
for meta == m.metas[index] {
|
|
kv_index := m.metas[index + 1]
|
|
if fast_string_eq(key, m.key_values.data[kv_index].key) {
|
|
for (m.metas[index + 2]>>hashbits) > 1 {
|
|
m.metas[index] = m.metas[index + 2] - probe_inc
|
|
m.metas[index + 1] = m.metas[index + 3]
|
|
index += 2
|
|
}
|
|
m.size--
|
|
m.metas[index] = 0
|
|
m.key_values.deletes++
|
|
C.memset(&m.key_values.data[kv_index], 0, sizeof(KeyValue))
|
|
if m.key_values.size <= 32 {
|
|
return
|
|
}
|
|
// Clean up key_values if too many have been deleted
|
|
if m.key_values.deletes >= (m.key_values.size >> 1) {
|
|
m.key_values.zeros_to_end()
|
|
m.rehash()
|
|
m.key_values.deletes = 0
|
|
}
|
|
return
|
|
}
|
|
index += 2
|
|
meta += probe_inc
|
|
}
|
|
}
|
|
|
|
// TODO: add optimization in case of no deletes
|
|
pub fn (m &map) keys() []string {
|
|
mut keys := [''].repeat(m.size)
|
|
mut j := 0
|
|
for i := u32(0); i < m.key_values.size; i++ {
|
|
if m.key_values.data[i].key.str == 0 {
|
|
continue
|
|
}
|
|
keys[j] = m.key_values.data[i].key
|
|
j++
|
|
}
|
|
return keys
|
|
}
|
|
|
|
[unsafe_fn]
|
|
pub fn (m map) free() {
|
|
free(m.metas)
|
|
for i := u32(0); i < m.key_values.size; i++ {
|
|
if m.key_values.data[i].key.str == 0 {
|
|
continue
|
|
}
|
|
m.key_values.data[i].key.free()
|
|
}
|
|
free(m.key_values.data)
|
|
}
|
|
|
|
pub fn (m map_string) str() string {
|
|
if m.size == 0 {
|
|
return '{}'
|
|
}
|
|
mut sb := strings.new_builder(50)
|
|
sb.writeln('{')
|
|
for key, val in m {
|
|
sb.writeln(' "$key" => "$val"')
|
|
}
|
|
sb.writeln('}')
|
|
return sb.str()
|
|
}
|