Fix SCRSift handling of large base points

gap-system · May 30, 2016 · ac5c474 · ac5c474
1 parent b9cd393
commit ac5c474
Show file tree

Hide file tree

Showing 2 changed files with 17 additions and 4 deletions.
diff --git a/src/permutat.c b/src/permutat.c
@@ -4823,10 +4823,18 @@ Obj FuncSCR_SIFT_HELPER(Obj self, Obj S, Obj g, Obj n)
     Obj orb = ElmPRec(stb,RN_orbit);
     Int bpt = INT_INTOBJ(ELM_LIST(orb,1))-1;
     Int im;
-    if (useP2)
-      im = (Int)ADDR_PERM2(result)[bpt];
-    else
-      im = (Int)ADDR_PERM4(result)[bpt];
+
+    if (useP2) {
+        UInt2* ptrResult = ADDR_PERM2(result);
+        UInt degResult = DEG_PERM2(result);
+        im = (Int)(IMAGE(bpt, ptrResult, degResult));
+    }
+    else {
+        UInt4* ptrResult = ADDR_PERM4(result);
+        UInt degResult = DEG_PERM2(result);
+        im = (Int)(IMAGE(bpt, ptrResult, degResult));
+    }
+
     if (!(t = ELM0_LIST(trans,im+1)))
       break;
     else {

diff --git a/tst/teststandard/bugfix.tst b/tst/teststandard/bugfix.tst
@@ -3101,6 +3101,11 @@ gap> Remove(l);
 gap> [l, Length(l)];
 [ [ 1, 2,, [  ] ], 4 ]
 
+#2016/05/30 (CJ, bug reported github #798)
+gap> sc := StabChainOp(Group((1,2)), rec(base := [3,2], reduced := false));;
+gap> SCRSift(sc, (1,2));
+()
+
 #############################################################################
 gap> STOP_TEST( "bugfix.tst", 831990000);