332 lines
11 KiB
Zig
332 lines
11 KiB
Zig
const std = @import("index.zig");
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const debug = std.debug;
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const assert = debug.assert;
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const math = std.math;
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const mem = std.mem;
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const Allocator = mem.Allocator;
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const builtin = @import("builtin");
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const want_modification_safety = builtin.mode != builtin.Mode.ReleaseFast;
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const debug_u32 = if (want_modification_safety) u32 else void;
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pub fn HashMap(comptime K: type, comptime V: type, comptime hash: fn (key: K) u32, comptime eql: fn (a: K, b: K) bool) type {
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return struct {
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entries: []Entry,
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size: usize,
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max_distance_from_start_index: usize,
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allocator: *Allocator,
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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 = this;
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pub const Entry = struct {
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used: bool,
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distance_from_start_index: usize,
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key: K,
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value: V,
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};
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pub const Iterator = struct {
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hm: *const Self,
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// how many items have we returned
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count: usize,
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// iterator through the entry array
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index: usize,
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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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// Reset the iterator to the initial index
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pub fn reset(it: *Iterator) void {
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it.count = 0;
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it.index = 0;
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// Resetting the modification count too
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it.initial_modification_count = it.hm.modification_count;
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}
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};
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pub fn init(allocator: *Allocator) Self {
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return Self{
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.entries = []Entry{},
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.allocator = allocator,
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.size = 0,
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.max_distance_from_start_index = 0,
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.modification_count = if (want_modification_safety) 0 else {},
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};
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}
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pub fn deinit(hm: *const Self) void {
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hm.allocator.free(hm.entries);
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}
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pub fn clear(hm: *Self) void {
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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.incrementModificationCount();
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}
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pub fn count(hm: *const Self) usize {
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return hm.size;
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}
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/// Returns the value that was already there.
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pub fn put(hm: *Self, key: K, value: *const V) !?V {
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if (hm.entries.len == 0) {
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try hm.initCapacity(16);
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}
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hm.incrementModificationCount();
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// if we get too full (60%), double the capacity
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if (hm.size * 5 >= hm.entries.len * 3) {
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const old_entries = hm.entries;
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try hm.initCapacity(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.internalPut(old_entry.key, old_entry.value);
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}
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}
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hm.allocator.free(old_entries);
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}
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return hm.internalPut(key, value);
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}
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pub fn get(hm: *const Self, key: K) ?*Entry {
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if (hm.entries.len == 0) {
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return null;
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}
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return hm.internalGet(key);
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}
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pub fn contains(hm: *const Self, key: K) bool {
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return hm.get(key) != null;
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}
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pub fn remove(hm: *Self, key: K) ?*Entry {
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if (hm.entries.len == 0) return null;
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hm.incrementModificationCount();
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const start_index = hm.keyToIndex(key);
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{
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var roll_over: usize = 0;
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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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if (!entry.used) return null;
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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 or 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 entry;
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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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}
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return null;
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}
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pub fn iterator(hm: *const 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 initCapacity(hm: *Self, capacity: usize) !void {
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hm.entries = try hm.allocator.alloc(Entry, capacity);
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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 incrementModificationCount(hm: *Self) void {
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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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/// Returns the value that was already there.
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fn internalPut(hm: *Self, orig_key: K, orig_value: *const V) ?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.keyToIndex(key);
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var roll_over: usize = 0;
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var distance_from_start_index: usize = 0;
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while (roll_over < hm.entries.len) : ({
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roll_over += 1;
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distance_from_start_index += 1;
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}) {
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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 and !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(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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var result: ?V = null;
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if (entry.used) {
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result = entry.value;
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} else {
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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(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 result;
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}
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unreachable; // put into a full map
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}
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fn internalGet(hm: *const Self, key: K) ?*Entry {
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const start_index = hm.keyToIndex(key);
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{
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var roll_over: usize = 0;
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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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}
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return null;
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}
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fn keyToIndex(hm: *const Self, key: K) usize {
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return usize(hash(key)) % hm.entries.len;
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}
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};
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}
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test "basic hash map usage" {
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var direct_allocator = std.heap.DirectAllocator.init();
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defer direct_allocator.deinit();
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var map = HashMap(i32, i32, hash_i32, eql_i32).init(&direct_allocator.allocator);
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defer map.deinit();
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assert((try map.put(1, 11)) == null);
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assert((try map.put(2, 22)) == null);
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assert((try map.put(3, 33)) == null);
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assert((try map.put(4, 44)) == null);
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assert((try map.put(5, 55)) == null);
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assert((try map.put(5, 66)).? == 55);
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assert((try map.put(5, 55)).? == 66);
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assert(map.contains(2));
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assert(map.get(2).?.value == 22);
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_ = map.remove(2);
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assert(map.remove(2) == null);
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assert(map.get(2) == null);
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}
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test "iterator hash map" {
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var direct_allocator = std.heap.DirectAllocator.init();
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defer direct_allocator.deinit();
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var reset_map = HashMap(i32, i32, hash_i32, eql_i32).init(&direct_allocator.allocator);
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defer reset_map.deinit();
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assert((try reset_map.put(1, 11)) == null);
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assert((try reset_map.put(2, 22)) == null);
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assert((try reset_map.put(3, 33)) == null);
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var keys = []i32{
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1,
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2,
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3,
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};
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var values = []i32{
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11,
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22,
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33,
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};
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var it = reset_map.iterator();
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var count: usize = 0;
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while (it.next()) |next| {
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assert(next.key == keys[count]);
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assert(next.value == values[count]);
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count += 1;
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}
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assert(count == 3);
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assert(it.next() == null);
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it.reset();
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count = 0;
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while (it.next()) |next| {
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assert(next.key == keys[count]);
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assert(next.value == values[count]);
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count += 1;
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if (count == 2) break;
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}
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it.reset();
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var entry = it.next().?;
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assert(entry.key == keys[0]);
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assert(entry.value == values[0]);
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}
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fn hash_i32(x: i32) u32 {
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return @bitCast(u32, x);
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}
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fn eql_i32(a: i32, b: i32) bool {
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return a == b;
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}
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