+ return (PGEN_DONE);
+ }
+
+ /* --- Continue stepping if necessary --- */
+
+ while (rc == PGEN_FAIL || qrc == PGEN_FAIL) {
+ rc = pfilt_step(&c->p, 4);
+ qrc = pfilt_step(&c->q, 2);
+ }
+
+ ev->m = MP_COPY(c->p.m);
+ if (qrc == PGEN_TRY)
+ rc = PGEN_TRY;
+ return (rc);
+}
+
+/* --- @pgen_safejump@ --- *
+ *
+ * Jumps two numbers, %$q$% and %$p = 2q + 1$% such that neither has any
+ * small factors.
+ */
+
+int pgen_safejump(int rq, pgen_event *ev, void *p)
+{
+ pgen_safejumpctx *j = p;
+ int rc = PGEN_ABORT, qrc = 0;
+
+ switch (rq) {
+
+ /* --- Set up the jump contexts --- *
+ *
+ * The jump in @j.q@ is congruent to 2 (mod 4); see @strongprime_setup@.
+ * If @p@ is initially 1 (mod 4) then add @j.q@. Then double @j.q@ to
+ * ensure that the step is 0 (mod 4). Ensure that @jq@ and @q@ don't
+ * have any common factors.
+ */
+
+ case PGEN_BEGIN: {
+ mp *p = ev->m;
+ mp *q;
+ mp *g = MP_NEW;
+ if ((p->v[0] & 3) != 3)
+ p = mp_add(p, p, j->jq.m);
+ q = mp_lsr(MP_NEW, p, 1);
+ mp_gcd(&g, 0, 0, p, j->jq.m);
+ if (MP_CMP(g, >, MP_ONE)) {
+ ev->m = p;
+ mp_drop(q);
+ mp_drop(g);
+ return (PGEN_ABORT);
+ }
+ mp_drop(g);
+ rc = pfilt_create(&j->p, p);
+ pfilt_muladd(&j->jp, &j->jq, 2, 0);
+ qrc = pfilt_create(&j->q, q);
+ mp_drop(p);
+ mp_drop(q);
+ } break;
+
+ /* --- Step on one place --- */
+
+ case PGEN_TRY:
+ mp_drop(ev->m);
+ rc = pfilt_jump(&j->p, &j->jp);
+ qrc = pfilt_jump(&j->q, &j->jq);