281 lines
9.0 KiB
Zig
281 lines
9.0 KiB
Zig
const assert = @import("index.zig").assert;
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const math = @import("math.zig");
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const mem = @import("mem.zig");
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const Allocator = mem.Allocator;
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const want_modification_safety = !@compile_var("is_release");
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const debug_u32 = if (want_modification_safety) u32 else void;
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/*
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pub fn HashMap(K: type, V: type, hash: fn(key: K)->u32, eql: fn(a: K, b: K)->bool) {
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SmallHashMap(K, V, hash, eql, 8);
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}
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*/
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pub struct SmallHashMap(K: type, V: type, hash: fn(key: K)->u32, eql: fn(a: K, b: K)->bool, STATIC_SIZE: isize) {
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entries: []Entry,
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size: isize,
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max_distance_from_start_index: isize,
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allocator: &Allocator,
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// if the hash map is small enough, we use linear search through these
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// entries instead of allocating memory
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prealloc_entries: [STATIC_SIZE]Entry,
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// this is used to detect bugs where a hashtable is edited while an iterator is running.
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modification_count: debug_u32,
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const Self = SmallHashMap(K, V, hash, eql, STATIC_SIZE);
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pub struct Entry {
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used: bool,
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distance_from_start_index: isize,
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key: K,
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value: V,
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}
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pub struct Iterator {
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hm: &Self,
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// how many items have we returned
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count: isize,
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// iterator through the entry array
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index: isize,
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// used to detect concurrent modification
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initial_modification_count: debug_u32,
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pub fn next(it: &Iterator) -> ?&Entry {
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if (want_modification_safety) {
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assert(it.initial_modification_count == it.hm.modification_count); // concurrent modification
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}
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if (it.count >= it.hm.size) return null;
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while (it.index < it.hm.entries.len; it.index += 1) {
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const entry = &it.hm.entries[it.index];
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if (entry.used) {
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it.index += 1;
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it.count += 1;
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return entry;
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}
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}
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unreachable{} // no next item
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}
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}
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pub fn init(hm: &Self, allocator: &Allocator) {
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hm.entries = hm.prealloc_entries[0...];
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hm.allocator = allocator;
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hm.size = 0;
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hm.max_distance_from_start_index = 0;
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for (hm.entries) |*entry| {
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entry.used = false;
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}
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}
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pub fn deinit(hm: &Self) {
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if (hm.entries.ptr != &hm.prealloc_entries[0]) {
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hm.allocator.free(hm.allocator, ([]u8)(hm.entries));
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}
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}
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pub fn clear(hm: &Self) {
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for (hm.entries) |*entry| {
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entry.used = false;
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}
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hm.size = 0;
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hm.max_distance_from_start_index = 0;
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hm.increment_modification_count();
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}
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pub fn put(hm: &Self, key: K, value: V) -> %void {
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hm.increment_modification_count();
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const resize = if (hm.entries.ptr == &hm.prealloc_entries[0]) {
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// preallocated entries table is full
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hm.size == hm.entries.len
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} else {
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// if we get too full (60%), double the capacity
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hm.size * 5 >= hm.entries.len * 3
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};
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if (resize) {
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const old_entries = hm.entries;
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%return hm.init_capacity(hm.entries.len * 2);
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// dump all of the old elements into the new table
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for (old_entries) |*old_entry| {
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if (old_entry.used) {
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hm.internal_put(old_entry.key, old_entry.value);
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}
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}
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if (old_entries.ptr != &hm.prealloc_entries[0]) {
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hm.allocator.free(hm.allocator, ([]u8)(old_entries));
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}
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}
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hm.internal_put(key, value);
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}
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pub fn get(hm: &Self, key: K) -> ?&Entry {
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return hm.internal_get(key);
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}
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pub fn remove(hm: &Self, key: K) {
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hm.increment_modification_count();
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const start_index = hm.key_to_index(key);
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{var roll_over: isize = 0; while (roll_over <= hm.max_distance_from_start_index; roll_over += 1) {
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const index = (start_index + roll_over) % hm.entries.len;
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var entry = &hm.entries[index];
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assert(entry.used); // key not found
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if (!eql(entry.key, key)) continue;
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while (roll_over < hm.entries.len; roll_over += 1) {
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const next_index = (start_index + roll_over + 1) % hm.entries.len;
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const next_entry = &hm.entries[next_index];
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if (!next_entry.used || next_entry.distance_from_start_index == 0) {
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entry.used = false;
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hm.size -= 1;
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return;
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}
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*entry = *next_entry;
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entry.distance_from_start_index -= 1;
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entry = next_entry;
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}
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unreachable{} // shifting everything in the table
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}}
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unreachable{} // key not found
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}
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pub fn entry_iterator(hm: &Self) -> Iterator {
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return Iterator {
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.hm = hm,
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.count = 0,
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.index = 0,
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.initial_modification_count = hm.modification_count,
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};
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}
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fn init_capacity(hm: &Self, capacity: isize) -> %void {
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hm.entries = ([]Entry)(%return hm.allocator.alloc(hm.allocator, capacity * @sizeof(Entry)));
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hm.size = 0;
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hm.max_distance_from_start_index = 0;
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for (hm.entries) |*entry| {
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entry.used = false;
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}
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}
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fn increment_modification_count(hm: &Self) {
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if (want_modification_safety) {
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hm.modification_count += 1;
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}
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}
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fn internal_put(hm: &Self, orig_key: K, orig_value: V) {
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var key = orig_key;
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var value = orig_value;
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const start_index = hm.key_to_index(key);
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var roll_over: isize = 0;
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var distance_from_start_index: isize = 0;
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while (roll_over < hm.entries.len; {roll_over += 1; distance_from_start_index += 1}) {
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const index = (start_index + roll_over) % hm.entries.len;
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const entry = &hm.entries[index];
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if (entry.used && !eql(entry.key, key)) {
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if (entry.distance_from_start_index < distance_from_start_index) {
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// robin hood to the rescue
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const tmp = *entry;
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hm.max_distance_from_start_index = math.max(isize)(
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hm.max_distance_from_start_index, distance_from_start_index);
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*entry = Entry {
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.used = true,
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.distance_from_start_index = distance_from_start_index,
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.key = key,
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.value = value,
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};
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key = tmp.key;
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value = tmp.value;
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distance_from_start_index = tmp.distance_from_start_index;
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}
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continue;
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}
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if (!entry.used) {
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// adding an entry. otherwise overwriting old value with
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// same key
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hm.size += 1;
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}
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hm.max_distance_from_start_index = math.max(isize)(distance_from_start_index, hm.max_distance_from_start_index);
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*entry = Entry {
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.used = true,
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.distance_from_start_index = distance_from_start_index,
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.key = key,
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.value = value,
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};
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return;
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}
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unreachable{} // put into a full map
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}
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fn internal_get(hm: &Self, key: K) -> ?&Entry {
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const start_index = hm.key_to_index(key);
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{var roll_over: isize = 0; while (roll_over <= hm.max_distance_from_start_index; roll_over += 1) {
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const index = (start_index + roll_over) % hm.entries.len;
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const entry = &hm.entries[index];
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if (!entry.used) return null;
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if (eql(entry.key, key)) return entry;
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}}
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return null;
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}
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fn key_to_index(hm: &Self, key: K) -> isize {
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return isize(hash(key)) % hm.entries.len;
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}
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}
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var global_allocator = Allocator {
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.alloc = global_alloc,
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.realloc = global_realloc,
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.free = global_free,
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.context = null,
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};
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var some_mem: [200]u8 = undefined;
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var some_mem_index: isize = 0;
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fn global_alloc(self: &Allocator, n: isize) -> %[]u8 {
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const result = some_mem[some_mem_index ... some_mem_index + n];
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some_mem_index += n;
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return result;
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}
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fn global_realloc(self: &Allocator, old_mem: []u8, new_size: isize) -> %[]u8 {
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const result = %return global_alloc(self, new_size);
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@memcpy(result.ptr, old_mem.ptr, old_mem.len);
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return result;
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}
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fn global_free(self: &Allocator, old_mem: []u8) {
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}
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#attribute("test")
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fn basic_hash_map_test() {
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var map: SmallHashMap(i32, i32, hash_i32, eql_i32, 4) = undefined;
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map.init(&global_allocator);
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defer map.deinit();
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%%map.put(1, 11);
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%%map.put(2, 22);
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%%map.put(3, 33);
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%%map.put(4, 44);
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%%map.put(5, 55);
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assert((??map.get(2)).value == 22);
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map.remove(2);
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assert(if (const entry ?= map.get(2)) false else true);
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}
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fn hash_i32(x: i32) -> u32 {
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*(&u32)(&x)
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}
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fn eql_i32(a: i32, b: i32) -> bool {
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a == b
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}
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