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make use of hasUniqueRepresentation to speed up hashing facilities, fastpath in getAutoHashFn is particularly important for hashmap performance

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gives a 1.18x speedup on gotta-go-fast hashmap bench
This commit is contained in:
Sahnvour 2020-07-26 22:08:48 +02:00
parent 345cb3200c
commit f67ce1e35f
2 changed files with 14 additions and 9 deletions
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12
lib/std/hash/auto_hash.zig
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@ -56,9 +56,6 @@ pub fn hashPointer(hasher: anytype, key: anytype, comptime strat: HashStrategy)
pub fn hashArray(hasher: anytype, key: anytype, comptime strat: HashStrategy) void { pub fn hashArray(hasher: anytype, key: anytype, comptime strat: HashStrategy) void {
switch (strat) { switch (strat) {
.Shallow => { .Shallow => {
// TODO detect via a trait when Key has no padding bits to
// hash it as an array of bytes.
// Otherwise, hash every element.
for (key) |element| { for (key) |element| {
hash(hasher, element, .Shallow); hash(hasher, element, .Shallow);
} }
@ -75,6 +72,12 @@ pub fn hashArray(hasher: anytype, key: anytype, comptime strat: HashStrategy) vo
/// Strategy is provided to determine if pointers should be followed or not. /// Strategy is provided to determine if pointers should be followed or not.
pub fn hash(hasher: anytype, key: anytype, comptime strat: HashStrategy) void { pub fn hash(hasher: anytype, key: anytype, comptime strat: HashStrategy) void {
const Key = @TypeOf(key); const Key = @TypeOf(key);
if (strat == .Shallow and comptime meta.trait.hasUniqueRepresentation(Key)) {
@call(.{ .modifier = .always_inline }, hasher.update, .{mem.asBytes(&key)});
return;
}
switch (@typeInfo(Key)) { switch (@typeInfo(Key)) {
.NoReturn, .NoReturn,
.Opaque, .Opaque,
@ -119,9 +122,6 @@ pub fn hash(hasher: anytype, key: anytype, comptime strat: HashStrategy) void {
}, },
.Struct => |info| { .Struct => |info| {
// TODO detect via a trait when Key has no padding bits to
// hash it as an array of bytes.
// Otherwise, hash every field.
inline for (info.fields) |field| { inline for (info.fields) |field| {
// We reuse the hash of the previous field as the seed for the // We reuse the hash of the previous field as the seed for the
// next one so that they're dependant. // next one so that they're dependant.

11
lib/std/hash_map.zig
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@ -5,6 +5,7 @@ const testing = std.testing;
const math = std.math; const math = std.math;
const mem = std.mem; const mem = std.mem;
const meta = std.meta; const meta = std.meta;
const trait = meta.trait;
const autoHash = std.hash.autoHash; const autoHash = std.hash.autoHash;
const Wyhash = std.hash.Wyhash; const Wyhash = std.hash.Wyhash;
const Allocator = mem.Allocator; const Allocator = mem.Allocator;
@ -1023,9 +1024,13 @@ pub fn getTrivialEqlFn(comptime K: type) (fn (K, K) bool) {
pub fn getAutoHashFn(comptime K: type) (fn (K) u32) { pub fn getAutoHashFn(comptime K: type) (fn (K) u32) {
return struct { return struct {
fn hash(key: K) u32 { fn hash(key: K) u32 {
var hasher = Wyhash.init(0); if (comptime trait.hasUniqueRepresentation(K)) {
autoHash(&hasher, key); return @truncate(u32, Wyhash.hash(0, std.mem.asBytes(&key)));
return @truncate(u32, hasher.final()); } else {
var hasher = Wyhash.init(0);
autoHash(&hasher, key);
return @truncate(u32, hasher.final());
}
} }
}.hash; }.hash;
} }