int main()
{
DUPFF f, g, cf, cg, h;
f = DUPFFnew(1); f->coeffs[1] = 1; f->deg = 1;
g = DUPFFnew(2); g->coeffs[2] = 1; g->deg = 2;
h = DUPFFexgcd(&cf, &cg, f, g);
h = h;
return 0;
}
DUPFF DUPFFexgcd(DUPFF *fcofac, DUPFF *gcofac, const DUPFF f, const DUPFF g)
{
DUPFF u, v, uf, ug, vf, vg;
FFelem q, lcu, lcvrecip, p;
int df, dg, du, dv;
if (DUPFFdeg(f) < DUPFFdeg(g)) return DUPFFexgcd(gcofac, fcofac, g, f);
if (DUPFFdeg(f) != 2 || DUPFFdeg(g) != 1) abort();
if (f->coeffs[0] == 0) return f;
p = 2;
df = DUPFFdeg(f); if (df < 0) df = 0; /* both inputs are zero */
dg = DUPFFdeg(g); if (dg < 0) dg = 0; /* one input is zero */
u = DUPFFcopy(f);
v = DUPFFcopy(g);
uf = DUPFFnew(dg); uf->coeffs[0] = 1; uf->deg = 0;
ug = DUPFFnew(df);
vf = DUPFFnew(dg);
vg = DUPFFnew(df); vg->coeffs[0] = 1; vg->deg = 0;
while (DUPFFdeg(v) > 0)
{
dv = DUPFFdeg(v);
lcvrecip = FFmul(1, v->coeffs[dv]);
while (DUPFFdeg(u) >= dv)
{
du = DUPFFdeg(u);
lcu = u->coeffs[du];
q = FFmul(lcu, lcvrecip);
DUPFFshift_add(u, v, du-dv, p-q);
DUPFFshift_add(uf, vf, du-dv, p-q);
DUPFFshift_add(ug, vg, du-dv, p-q);
}
DUPFFswap(u, v);
DUPFFswap(uf, vf);
DUPFFswap(ug, vg);
}
if (DUPFFdeg(v) == 0)
{
DUPFFswap(u, v);
DUPFFswap(uf, vf);
DUPFFswap(ug, vg);
}
DUPFFfree(vf);
DUPFFfree(vg);
DUPFFfree(v);
*fcofac = uf;
*gcofac = ug;
return u;
}
DUPFF DMPZ_to_DUPFF(DMPZ f, int var, int *substitution)
{
FFelem p = CurrentFF.prime;
int df, d, c, i;
DUPFF ans;
DMPZ iter;
df = DMPZdeg(f, var);
ans = DUPFFnew(df);
for(i=0; i<=df;i++) ans->coeffs[i] = 0;
for(iter=f;iter;iter = iter->next)
{
d = iter->exps[var];
c = mpz_fdiv_ui(iter->coeff, p);
for(i=0; c!=0 && i<NVARS;i++)
if (i != var)
c = FFmul(c, FFpow(substitution[i], iter->exps[i]));
ans->coeffs[d] += c;
if (ans->coeffs[d] >= p) ans->coeffs[d] -= p;
}
for(i=df;i>=0;i--) if (ans->coeffs[i] != 0) break;
ans->deg = i;
return ans;
}