static void
choose_prime(primedata *S, GEN pol, GEN dpol)
{
byteptr di = diffptr + 1;
long i, j, k, r, lcm, oldlcm, pp, N = degpol(pol), minp = N*N / 4;
GEN Z, p, ff, oldff, n, oldn;
pari_sp av;
if (DEBUGLEVEL) (void)timer2();
p = utoipos(2);
while (p[2] <= minp) NEXT_PRIME_VIADIFF(p[2], di);
oldlcm = 0;
oldff = oldn = NULL; pp = 0; /* gcc -Wall */
av = avma;
for(k = 1; k < 11 || !oldlcm; k++,avma = av)
{
do NEXT_PRIME_VIADIFF(p[2], di); while (!smodis(dpol, p[2]));
if (k > 5 * N) pari_err(talker,"sorry, too many block systems in nfsubfields");
ff = (GEN)FpX_factor(pol, p)[1];
r = lg(ff)-1;
if (r == N || r >= BIL) continue;
n = cgetg(r+1, t_VECSMALL); lcm = n[1] = degpol(ff[1]);
for (j=2; j<=r; j++) { n[j] = degpol(ff[j]); lcm = clcm(lcm, n[j]); }
if (lcm <= oldlcm) continue; /* false when oldlcm = 0 */
if (DEBUGLEVEL) fprintferr("p = %ld,\tlcm = %ld,\torbits: %Z\n",p[2],lcm,n);
pp = p[2];
oldn = n;
oldff = ff;
oldlcm = lcm; if (r == 1) break;
av = avma;
}
if (DEBUGLEVEL) fprintferr("Chosen prime: p = %ld\n", pp);
S->ff = oldff;
S->lcm= oldlcm;
S->p = utoipos(pp);
S->pol = FpX_red(pol, S->p); init_primedata(S);
n = oldn; r = lg(n); Z = cgetg(r,t_VEC);
for (k=0,i=1; i<r; i++)
{
GEN t = cgetg(n[i]+1, t_VECSMALL); gel(Z,i) = t;
for (j=1; j<=n[i]; j++) t[j] = ++k;
}
S->Z = Z;
}
// Digit reversal
GEN
rev(GEN n, long B)
{
pari_sp av = avma;
if (typ(n) != t_INT)
pari_err_TYPE("rev", n);
GEN m = modis(n, B);
n = divis(n, B);
pari_sp btop = avma, st_lim = stack_lim(btop, 1);
while (signe(n)) {
m = addis(mulis(m, B), smodis(n, B));
n = divis(n, B);
if (low_stack(st_lim, stack_lim(btop, 1)))
gerepileall(btop, 2, &m, &n);
}
m = gerepilecopy(av, m);
return m;
}
