avoid infinite loop in random_torsion_point

modcurve/torsion-subscheme.c

@@ -121,7 +121,7 @@ find_extension(GEN group, unsigned long l, unsigned long p,
 
 /* Naïve algorithm for finding a random  l-torsion point.  */
 static GEN
-random_torsion_point(GEN J, unsigned long l) {
+random_torsion_point(GEN J, unsigned long l, int *tries) {
   GEN n, m;
   long v;
   GEN P, Q;
@@ -132,7 +132,7 @@ random_torsion_point(GEN J, unsigned long l) {
   if(v == 0)
     pari_err(e_MISC, "no point of order %li", l);
   m = gdiv(n, powuu(l, v));
-  while(1) {
+  while((*tries)-- > 0) {
     err_printf("finding random point\n");
     P = jacobian_random_point(J);
     err_printf("multiplying by %Ps\n", m);
@@ -186,8 +186,8 @@ find_bases(GEN J, unsigned long l, GEN f, GEN proj, int tries,
   *matrices = cgetg(n + 1, t_VEC);
   for (i = 1; i <= n; i++)
     gel(*bases, i) = cgetg(1, t_VEC);
-  while (tries-- > 0 && found < 2*n) {
-    P = random_torsion_point(J, l);
+  while (tries > 0 && found < 2*n) {
+    P = random_torsion_point(J, l, &tries);
     for(i = 1; i <= n; i++) {
       j = lg(gel(*bases, i)) - 1;
       if (j == 2)