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std hash map: do the pow2 improvement again

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it's a noticeable speedup
This commit is contained in:
Andrew Kelley 2020-07-04 02:07:27 +00:00
parent 632acffcbd
commit 3c8b13d998
1 changed files with 25 additions and 21 deletions
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46
lib/std/hash_map.zig
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@ -382,22 +382,24 @@ pub fn HashMapUnmanaged(
try self.entries.ensureCapacity(allocator, new_capacity);
if (new_capacity <= linear_scan_max) return;
// Resize if indexes would be more than 60% full.
// Ensure that the indexes will be at most 60% full if
// `new_capacity` items are put into it.
const needed_len = new_capacity * 5 / 3;
if (self.index_header) |header| {
if (needed_len > header.indexes_len) {
var new_indexes_len = header.indexes_len;
while (true) {
new_indexes_len *= new_indexes_len / 2 + 8;
if (new_indexes_len >= needed_len) break;
}
// An overflow here would mean the amount of memory required would not
// be representable in the address space.
const new_indexes_len = math.ceilPowerOfTwo(usize, needed_len) catch unreachable;
const new_header = try IndexHeader.alloc(allocator, new_indexes_len);
self.insertAllEntriesIntoNewHeader(new_header);
header.free(allocator);
self.index_header = new_header;
}
} else {
const header = try IndexHeader.alloc(allocator, needed_len);
// An overflow here would mean the amount of memory required would not
// be representable in the address space.
const new_indexes_len = math.ceilPowerOfTwo(usize, needed_len) catch unreachable;
const header = try IndexHeader.alloc(allocator, new_indexes_len);
self.insertAllEntriesIntoNewHeader(header);
self.index_header = header;
}
@ -540,10 +542,10 @@ pub fn HashMapUnmanaged(
fn removeInternal(self: *Self, key: K, header: *IndexHeader, comptime I: type) ?Entry {
const indexes = header.indexes(I);
const h = hash(key);
const start_index = header.hashToIndex(h);
const start_index = header.constrainIndex(h);
var roll_over: usize = 0;
while (roll_over <= header.max_distance_from_start_index) : (roll_over += 1) {
const index_index = (start_index + roll_over) % header.indexes_len;
const index_index = header.constrainIndex(start_index + roll_over);
var index = &indexes[index_index];
if (index.isEmpty())
return null;
@ -564,7 +566,7 @@ pub fn HashMapUnmanaged(
// Now we have to shift over the following indexes.
roll_over += 1;
while (roll_over < header.indexes_len) : (roll_over += 1) {
const next_index_index = (start_index + roll_over) % header.indexes_len;
const next_index_index = header.constrainIndex(start_index + roll_over);
const next_index = &indexes[next_index_index];
if (next_index.isEmpty() or next_index.distance_from_start_index == 0) {
index.setEmpty();
@ -588,10 +590,10 @@ pub fn HashMapUnmanaged(
indexes: []Index(I),
) void {
const h = if (store_hash) self.entries.items[new_entry_index].hash else hash(self.entries.items[new_entry_index].key);
const start_index = header.hashToIndex(h);
const start_index = header.constrainIndex(h);
var roll_over: usize = 0;
while (roll_over <= header.max_distance_from_start_index) : (roll_over += 1) {
const index_index = (start_index + roll_over) % header.indexes_len;
const index_index = header.constrainIndex(start_index + roll_over);
const index = &indexes[index_index];
if (index.entry_index == old_entry_index) {
index.entry_index = @intCast(I, new_entry_index);
@ -605,14 +607,14 @@ pub fn HashMapUnmanaged(
fn getOrPutInternal(self: *Self, key: K, header: *IndexHeader, comptime I: type) GetOrPutResult {
const indexes = header.indexes(I);
const h = hash(key);
const start_index = header.hashToIndex(h);
const start_index = header.constrainIndex(h);
var roll_over: usize = 0;
var distance_from_start_index: usize = 0;
while (roll_over <= header.indexes_len) : ({
roll_over += 1;
distance_from_start_index += 1;
}) {
const index_index = (start_index + roll_over) % header.indexes_len;
const index_index = header.constrainIndex(start_index + roll_over);
const index = indexes[index_index];
if (index.isEmpty()) {
indexes[index_index] = .{
@ -670,7 +672,7 @@ pub fn HashMapUnmanaged(
roll_over += 1;
distance_from_start_index += 1;
}) {
const next_index_index = (start_index + roll_over) % header.indexes_len;
const next_index_index = header.constrainIndex(start_index + roll_over);
const next_index = indexes[next_index_index];
if (next_index.isEmpty()) {
header.maybeBumpMax(distance_from_start_index);
@ -702,10 +704,10 @@ pub fn HashMapUnmanaged(
fn getInternal(self: Self, key: K, header: *IndexHeader, comptime I: type) ?*Entry {
const indexes = header.indexes(I);
const h = hash(key);
const start_index = header.hashToIndex(h);
const start_index = header.constrainIndex(h);
var roll_over: usize = 0;
while (roll_over <= header.max_distance_from_start_index) : (roll_over += 1) {
const index_index = (start_index + roll_over) % header.indexes_len;
const index_index = header.constrainIndex(start_index + roll_over);
const index = indexes[index_index];
if (index.isEmpty())
return null;
@ -731,7 +733,7 @@ pub fn HashMapUnmanaged(
const indexes = header.indexes(I);
entry_loop: for (self.entries.items) |entry, i| {
const h = if (store_hash) entry.hash else hash(entry.key);
const start_index = header.hashToIndex(h);
const start_index = header.constrainIndex(h);
var entry_index = i;
var roll_over: usize = 0;
var distance_from_start_index: usize = 0;
@ -739,7 +741,7 @@ pub fn HashMapUnmanaged(
roll_over += 1;
distance_from_start_index += 1;
}) {
const index_index = (start_index + roll_over) % header.indexes_len;
const index_index = header.constrainIndex(start_index + roll_over);
const next_index = indexes[index_index];
if (next_index.isEmpty()) {
header.maybeBumpMax(distance_from_start_index);
@ -814,8 +816,10 @@ const IndexHeader = struct {
max_distance_from_start_index: usize,
indexes_len: usize,
fn hashToIndex(header: IndexHeader, h: u32) usize {
return @as(usize, h) % header.indexes_len;
fn constrainIndex(header: IndexHeader, i: usize) usize {
// This is an optimization for modulo of power of two integers;
// it requires `indexes_len` to always be a power of two.
return i & (header.indexes_len - 1);
}
fn indexes(header: *IndexHeader, comptime I: type) []Index(I) {