-/*----- Data structures ---------------------------------------------------*/
-
-typedef struct gcdctx {
- mp *q, *jq;
- pfilt p, jp;
- mp *r;
-} gcdctx;
-
-/*----- Custom stepper ----------------------------------------------------*/
-
-static int gcdstep(int rq, pgen_event *ev, void *p)
-{
- gcdctx *g = p;
- int rc = PGEN_ABORT;
- mp *z = MP_NEW;
-
- switch (rq) {
-
- /* --- Set everything up --- */
-
- case PGEN_BEGIN: {
- mp *p = ev->m;
- if ((p->v[0] & 3) != 3)
- p = mp_add(p, p, g->jp.m);
- rc = pfilt_create(&g->p, p);
- g->q = mp_lsr(MP_NEW, p, 1);
- g->jq = MP_COPY(g->jp.m);
- pfilt_muladd(&g->jp, &g->jp, 2, 0);
- g->jq = mp_lsr(MP_NEW, p, 1);
- mp_drop(p);
- } break;
-
- /* --- Grind through another iteration --- */
-
- case PGEN_TRY:
- mp_drop(ev->m);
- rc = pfilt_jump(&g->p, &g->jp);
- g->q = mp_add(g->q, g->q, g->jq);
- break;
-
- /* --- Finished --- */
-
- case PGEN_DONE:
- pfilt_destroy(&g->p);
- mp_drop(g->q);
- mp_drop(g->jq);
- return (PGEN_DONE);
- }
-
- /* --- Step on until everything is OK --- */
-
- for (;;) {
- if (rc != PGEN_FAIL) {
- mp_gcd(&z, 0, 0, g->r, g->q);
- if (MP_CMP(z, !=, MP_ONE))
- rc = PGEN_FAIL;
- }
- if (rc != PGEN_FAIL)
- break;
- rc = pfilt_jump(&g->p, &g->jp);
- g->q = mp_add(g->q, g->q, g->jq);
- }
-
- mp_drop(z);
- ev->m = MP_COPY(g->p.m);
- return (rc);
-}
-