From 818dd21a4fb1a3f52297537569bfa94eaae18cfb Mon Sep 17 00:00:00 2001
From: Michael Eischer <9106997+MichaelEischer@users.noreply.github.com>
Date: Fri, 25 Sep 2026 22:05:12 +0200
Subject: [PATCH] index: hash blob IDs with maphash.Bytes (#22070)

Avoid constructing a maphash.Hash on every lookup and insert.
---
 internal/repository/index/indexmap.go | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/internal/repository/index/indexmap.go b/internal/repository/index/indexmap.go
index d38385aba..f3db6ff5f 100644
--- a/internal/repository/index/indexmap.go
+++ b/internal/repository/index/indexmap.go
@@ -31,7 +31,7 @@ type indexMap struct {
 	buckets    []uint
 	numentries uint
 
-	mh maphash.Hash
+	seed maphash.Seed
 
 	blockList hashedArrayTree
 }
@@ -176,15 +176,13 @@ func (m *indexMap) hash(id restic.ID) uint {
 	// While SHA-256 should be collision-resistant, for hash table indices
 	// we use only a few bits of it and finding collisions for those is
 	// much easier than breaking the whole algorithm.
-	mh := maphash.Hash{}
-	mh.SetSeed(m.mh.Seed())
-	_, _ = mh.Write(id[:])
-	h := uint(mh.Sum64())
+	h := uint(maphash.Bytes(m.seed, id[:]))
 	return h & uint(len(m.buckets)-1)
 }
 
 func (m *indexMap) init() {
 	const initialBuckets = 64
+	m.seed = maphash.MakeSeed()
 	m.buckets = make([]uint, initialBuckets)
 	// first entry in blockList serves as null byte
 	m.blockList = *newHAT()