authorgravatar for sentientwaffle@gmail.comdjg <sentientwaffle@gmail.com> 2022-01-10 20:54:45-08:00
committergravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2022-01-12 11:58:24-07:00
log9b97edb01223d83095df35d5651572d796baae39
treeca8d1d664623a4185f88947d1fde9ab988fe67f0
parent1c6103825543bbbc37cdc60d9d9609c5625454f3

std: hash_map: optimize isFree/isTombstone (#10562)

- Add an `Metadata.isFree` helper method. - Implement `Metadata.isTombstone` and `Metadata.isFree` with `@bitCast` then comparing to a constant. I assume `@bitCast`-then-compare is faster than the old method because it only involves one comparison, and doesn't require bitmasking. - Summary of benchmarked changes (`gotta-go-fast`, run locally, compared to master): - 3/4 of the hash map benchmarks used ~10% fewer cycles - The last one (project Euler) shows 4% fewer cycles.

1 files changed, 10 insertions(+), 3 deletions(-)

lib/std/hash_map.zig+10-3
......@@ -750,12 +750,19 @@ pub fn HashMapUnmanaged(
750750 fingerprint: FingerPrint = free,
751751 used: u1 = 0,
752752
753 const slot_free = @bitCast(u8, Metadata{ .fingerprint = free });
754 const slot_tombstone = @bitCast(u8, Metadata{ .fingerprint = tombstone });
755
753756 pub fn isUsed(self: Metadata) bool {
754757 return self.used == 1;
755758 }
756759
757760 pub fn isTombstone(self: Metadata) bool {
758 return !self.isUsed() and self.fingerprint == tombstone;
761 return @bitCast(u8, self) == slot_tombstone;
762 }
763
764 pub fn isFree(self: Metadata) bool {
765 return @bitCast(u8, self) == slot_free;
759766 }
760767
761768 pub fn takeFingerprint(hash: Hash) FingerPrint {
......@@ -1115,7 +1122,7 @@ pub fn HashMapUnmanaged(
11151122 var idx = @truncate(usize, hash & mask);
11161123
11171124 var metadata = self.metadata.? + idx;
1118 while ((metadata[0].isUsed() or metadata[0].isTombstone()) and limit != 0) {
1125 while (!metadata[0].isFree() and limit != 0) {
11191126 if (metadata[0].isUsed() and metadata[0].fingerprint == fingerprint) {
11201127 const test_key = &self.keys()[idx];
11211128 // If you get a compile error on this line, it means that your generic eql
......@@ -1294,7 +1301,7 @@ pub fn HashMapUnmanaged(
12941301
12951302 var first_tombstone_idx: usize = self.capacity(); // invalid index
12961303 var metadata = self.metadata.? + idx;
1297 while ((metadata[0].isUsed() or metadata[0].isTombstone()) and limit != 0) {
1304 while (!metadata[0].isFree() and limit != 0) {
12981305 if (metadata[0].isUsed() and metadata[0].fingerprint == fingerprint) {
12991306 const test_key = &self.keys()[idx];
13001307 // If you get a compile error on this line, it means that your generic eql