dirichlet_group_init: return flag instead of abort when prime factor is too large

Author: fredrik-johansson

dirichlet.h

@@ -64,7 +64,7 @@ dirichlet_group_size(const dirichlet_group_t G)
 
 ulong dirichlet_group_num_primitive(const dirichlet_group_t G);
 
-void dirichlet_group_init(dirichlet_group_t G, ulong q);
+int dirichlet_group_init(dirichlet_group_t G, ulong q);
 void dirichlet_subgroup_init(dirichlet_group_t H, const dirichlet_group_t G, ulong h);
 void dirichlet_group_clear(dirichlet_group_t G);
 void dirichlet_group_dlog_precompute(dirichlet_group_t G, ulong num);

dirichlet/group_init.c

@@ -103,7 +103,7 @@ dirichlet_group_lift_generators(dirichlet_group_t G)
     }
 }
 
-void
+int
 dirichlet_group_init(dirichlet_group_t G, ulong q)
 {
     slong k;
@@ -123,6 +123,12 @@ dirichlet_group_init(dirichlet_group_t G, ulong q)
     n_factor_init(&fac);
     n_factor(&fac, q, 1);
 
+#if FLINT_BITS == 64
+    for (k = 0; k < fac.num; k++)
+        if (fac.p[k] > UWORD(1000000000000))
+            return 0;
+#endif
+
     G->num = fac.num + G->neven;
     G->P = flint_malloc(G->num * sizeof(dirichlet_prime_group_struct));
     G->generators = flint_malloc(G->num * sizeof(ulong));
@@ -145,6 +151,8 @@ dirichlet_group_init(dirichlet_group_t G, ulong q)
         dirichlet_prime_group_init(&G->P[k], p, e);
     }
     dirichlet_group_lift_generators(G);
+
+    return 1;
 }
 
 void

doc/source/dirichlet.rst

@@ -48,7 +48,7 @@ Multiplicative group modulo *q*
     An *dirichlet_group_t* is defined as an array of *dirichlet_group_struct*
     of length 1, permitting it to be passed by reference.
 
-.. function:: void dirichlet_group_init(dirichlet_group_t G, ulong q)
+.. function:: int dirichlet_group_init(dirichlet_group_t G, ulong q)
 
     Initializes *G* to the group of Dirichlet characters mod *q*.
 
@@ -69,8 +69,9 @@ Multiplicative group modulo *q*
     safely be called even with large *q*.
 
     For implementation reasons, the largest prime factor of *q* must not
-    exceed `10^{12}` (an abort will be raised). This restriction could
-    be removed in the future.
+    exceed `10^{12}`. This restriction could
+    be removed in the future. The function returns 1 on success and 0
+    if a factor is too large.
 
 .. function:: void dirichlet_subgroup_init(dirichlet_group_t H, const dirichlet_group_t G, ulong h)