From 19484a75098d43e75e3facfdd05dccefc358e43f Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Fri, 11 Oct 2024 14:54:29 +0200
Subject: [PATCH] Fix hashing for integer plists (#5807)

---
 lib/dicthf.gi                            |  2 +-
 tst/testbugfix/2024-10-11-orbit-hash.tst | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 tst/testbugfix/2024-10-11-orbit-hash.tst

diff --git a/lib/dicthf.gi b/lib/dicthf.gi
index e4349ac940..119d5329f6 100644
--- a/lib/dicthf.gi
+++ b/lib/dicthf.gi
@@ -164,7 +164,7 @@ function(m, v)
     if not IsPlistRep(x) then
       x := AsPlist(x);
     fi;
-    return HashKeyWholeBag(x, 1);
+    return HashKeyBag(x, 1, 0, Length(x) * GAPInfo.BytesPerVariable);
   end;
 
   # alternative code w/o HashKeyBag
diff --git a/tst/testbugfix/2024-10-11-orbit-hash.tst b/tst/testbugfix/2024-10-11-orbit-hash.tst
new file mode 100644
index 0000000000..3735537e6f
--- /dev/null
+++ b/tst/testbugfix/2024-10-11-orbit-hash.tst
@@ -0,0 +1,20 @@
+# Fix a bug reported by Leonard Soicher caused by a bug in
+# the hash function for lists of small positive integers.
+gap> n:=280;;
+gap> G:=OnePrimitiveGroup(NrMovedPoints,n,Size,604800*2);
+J_2.2
+gap> blocks := [ [ 1, 2, 3, 28, 108, 119, 155, 198, 216, 226 ],
+>  [ 1, 2, 3, 118, 119, 140, 193, 213, 218, 226 ] ];;
+gap> Append(blocks[2],[1..1000]); for i in [1..1000] do Remove(blocks[2]); od;
+gap> Append(blocks[2],[1..1000]); for i in [1..1000] do Remove(blocks[2]); od;
+gap> ForAll(blocks,IsSet);
+true
+gap> orb1:=Orbit(G,blocks[1],OnSets);;
+gap> Length(orb1);
+12096
+gap> orb2:=Orbit(G,blocks[2],OnSets);;
+gap> Length(orb2);
+1008
+gap> orbs:=Orbits(G,blocks,OnSets);;
+gap> List(orbs,Length); # this code gave wrong results
+[ 12096, 1008 ]