From: Michael Pratt <mpratt@google.com>
Date: Mon, 12 Aug 2024 20:38:58 +0000 (-0400)
Subject: internal/runtime/maps: speed up modulo
X-Git-Tag: go1.24rc1~567
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=bb46b754bebb0e820d74fd9eb02635afbdf5a3bd;p=gostls13.git

internal/runtime/maps: speed up modulo

For #54766.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest-swissmap
Change-Id: Ic47721e101f6fee650e6825a5a241fcd12fa0009
Reviewed-on: https://go-review.googlesource.com/c/go/+/611185
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
---

diff --git a/src/internal/runtime/maps/table.go b/src/internal/runtime/maps/table.go
index 60f4263100..232c077db3 100644
--- a/src/internal/runtime/maps/table.go
+++ b/src/internal/runtime/maps/table.go
@@ -571,7 +571,7 @@ func (it *Iter) Next() {
 		//
 		// We could avoid most of these lookups if we left a flag
 		// behind on the old table to denote that it is stale.
-		dirIdx := int((uint64(it.dirIdx) + it.dirOffset) % uint64(len(it.m.directory)))
+		dirIdx := int((uint64(it.dirIdx) + it.dirOffset) & uint64(len(it.m.directory)-1))
 		newTab := it.m.directory[dirIdx]
 		if it.tab == nil {
 			if newTab.index != dirIdx {