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kernel: fix issues with assumptions in IS_ACYCLIC_DIGRAPH #901

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Merged
james-d-mitchell merged 2 commits into from
Feb 27, 2026
Merged

kernel: fix issues with assumptions in IS_ACYCLIC_DIGRAPH #901

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e084b83
kernel: fix issues with assumptions in IS_ACYCLIC_DIGRAPH
james-d-mitchell Feb 25, 2026
243a21d
Add failing example to tests
reiniscirpons Feb 27, 2026
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18 changes: 9 additions & 9 deletions src/digraphs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -405,14 +405,14 @@ static Obj FuncIS_ACYCLIC_DIGRAPH(Obj self, Obj adj) {
Obj nbs;
UInt *stack, *ptr;

nr = LEN_PLIST(adj);
nr = LEN_LIST(adj);

// init the buf
ptr = safe_calloc(nr + 1, sizeof(UInt));
stack = safe_malloc((2 * nr + 2) * sizeof(UInt));

for (i = 1; i <= nr; i++) {
nbs = ELM_PLIST(adj, i);
nbs = ELM_LIST(adj, i);
if (LEN_LIST(nbs) == 0) {
ptr[i] = 1;
} else if (ptr[i] == 0) {
Expand All @@ -431,7 +431,7 @@ static Obj FuncIS_ACYCLIC_DIGRAPH(Obj self, Obj adj) {
// Check whether:
// 1. We've previously finished with this vertex, OR
// 2. Whether we've now investigated all descendant branches
nbs = ELM_PLIST(adj, j);
nbs = ELM_LIST(adj, j);
if (ptr[j] == 1 || k > (UInt) LEN_LIST(nbs)) {
ptr[j] = 1;
level--;
Expand All @@ -445,9 +445,9 @@ static Obj FuncIS_ACYCLIC_DIGRAPH(Obj self, Obj adj) {
} else { // Otherwise move onto the next available branch
ptr[j] = 2;
level++;
nbs = ELM_PLIST(adj, j);
nbs = ELM_LIST(adj, j);
stack += 2;
stack[0] = INT_INTOBJ(CONST_ADDR_OBJ(nbs)[k]);
stack[0] = INT_INTOBJ(ELM_LIST(nbs, k));
stack[1] = 1;
}
}
Expand Down Expand Up @@ -1359,10 +1359,10 @@ static Obj FuncDIGRAPH_REFLEX_TRANS_CLOSURE(Obj self, Obj digraph) {
}

static Obj FuncRANDOM_DIGRAPH(Obj self, Obj nn, Obj pp) {
UInt n, i, j;
Double p, q;
Int len;
Obj adj, adji;
UInt n, i, j;
Double p, q;
Int len;
Obj adj, adji;

n = INT_INTOBJ(nn);
p = VAL_MACFLOAT(pp);
Expand Down
8 changes: 8 additions & 0 deletions tst/standard/prop.tst
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,14 @@ gap> HasIsAcyclicDigraph(gr);
false
gap> IsAcyclicDigraph(gr);
false
gap> IsAcyclicDigraph(Digraph([[2 .. 3], [], []]));
true
gap> IsAcyclicDigraph(Digraph([[2 .. 4], [], [], []]));
true
gap> IsAcyclicDigraph(Digraph([[1 .. 3], [1 .. 3], [1 .. 3]]));
false
gap> IsAcyclicDigraph(Digraph([[2 .. 4], [1 .. 4], [1 .. 4], [1 .. 2]]));
false

# IsFunctionalDigraph
gap> IsFunctionalDigraph(multiple);
Expand Down
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