/* pol^2 mod (x^2+x+1, N) */
static GEN
sqrmod3(GEN pol, Red *R)
{
GEN a,b,bma,A,B;
long lv = lg(pol);
if (lv==2) return pol;
if (lv==3) return sqrconst(pol, R);
a = gel(pol,3);
b = gel(pol,2); bma = subii(b,a);
A = centermodii(mulii(a,addii(b,bma)), R->N, R->N2);
B = centermodii(mulii(bma,addii(a,b)), R->N, R->N2);
return makepoldeg1(A,B);
}
/* S1 * u - P1 * round(P^-1 S u). K non-zero coords in u given by ind */
static GEN
get_trace(GEN ind, trace_data *T)
{
long i, j, l, K = lg(ind)-1;
GEN z, s, v;
s = gel(T->S1, ind[1]);
if (K == 1) return s;
/* compute s = S1 u */
for (j=2; j<=K; j++) s = gadd(s, gel(T->S1, ind[j]));
/* compute v := - round(P^1 S u) */
l = lg(s);
v = cgetg(l, t_VECSMALL);
for (i=1; i<l; i++)
{
double r, t = 0.;
/* quick approximate computation */
for (j=1; j<=K; j++) t += T->PinvSdbl[ ind[j] ][i];
r = floor(t + 0.5);
if (fabs(t + 0.5 - r) < 0.0001)
{ /* dubious, compute exactly */
z = gen_0;
for (j=1; j<=K; j++) z = addii(z, ((GEN**)T->dPinvS)[ ind[j] ][i]);
v[i] = - itos( diviiround(z, T->d) );
}
else
v[i] = - (long)r;
}
return gadd(s, ZM_zc_mul(T->P1, v));
}
GEN
F2xq_ellcard(GEN a, GEN a6, GEN T)
{
pari_sp av = avma;
long n = F2x_degree(T);
GEN q = int2u(n), c;
if (typ(a)==t_VECSMALL)
{
GEN t = F2xq_elltrace_Harley(a6, T);
c = addii(q, F2xq_trace(a,T) ? addui(1,t): subui(1,t));
} else if (n==1)
{
long a4i = lgpol(gel(a,2)), a6i = lgpol(a6);
return utoi(a4i? (a6i? 1: 5): 3);
}
else if (n==2)
{
GEN a3 = gel(a,1), a4 = gel(a,2), x = polx_F2x(T[1]), x1 = pol1_F2x(T[1]);
GEN a613 = F2xq_mul(F2x_add(x1, a6),a3,T), a43= F2xq_mul(a4,a3,T);
long f0= F2xq_trace(F2xq_mul(a6,a3,T),T);
long f1= F2xq_trace(F2x_add(a43,a613),T);
long f2= F2xq_trace(F2x_add(F2xq_mul(a43,x,T),a613),T);
long f3= F2xq_trace(F2x_add(F2xq_mul(a43,F2x_add(x,x1),T),a613),T);
c = utoi(9-2*(f0+f1+f2+f3));
}
else
{
struct _F2xqE e;
long m = (n+1)>>1;
GEN q1 = addis(q, 1);
GEN v = n==4 ? mkvec4s(13,17,21,25)
: odd(n) ? mkvec3(subii(q1,int2u(m)),q1,addii(q1,int2u(m))):
mkvec5(subii(q1,int2u(m+1)),subii(q1,int2u(m)),q1,
addii(q1,int2u(m)),addii(q1,int2u(m+1)));
e.a2=a; e.a6=a6; e.T=T;
c = gen_select_order(v,(void*)&e, &F2xqE_group);
if (n==4 && equaliu(c, 21)) /* Ambiguous case */
{
GEN d = F2xq_powu(polx_F2x(T[1]),3,T), a3 = gel(a,1);
e.a6 = F2x_add(a6,F2xq_mul(d,F2xq_sqr(a3,T),T)); /* twist */
c = subui(34, gen_select_order(mkvec2s(13,25),(void*)&e, &F2xqE_group));
}
}
return gerepileuptoint(av, c);
}
/* Return a subfield, gen_0 [ change p ] or NULL [ not a subfield ] */
static GEN
subfield(GEN A, blockdata *B)
{
long N, i, j, d, lf, m = lg(A)-1;
GEN M, pe, pol, fhk, g, e, d_1_term, delta, listdelta, whichdelta;
GEN T = B->S->T, p = B->S->p, firstroot = B->S->firstroot;
pol= (GEN)B->DATA[1]; N = degpol(pol); d = N/m; /* m | N */
pe = (GEN)B->DATA[2];
fhk= (GEN)B->DATA[3];
M = (GEN)B->DATA[8];
delta = cgetg(m+1,t_VEC);
whichdelta = cgetg(N+1, t_VECSMALL);
d_1_term = gen_0;
for (i=1; i<=m; i++)
{
GEN Ai = gel(A,i), p1 = (GEN)fhk[Ai[1]];
for (j=2; j<=d; j++)
p1 = Fq_mul(p1, (GEN)fhk[Ai[j]], T, pe);
gel(delta,i) = p1;
if (DEBUGLEVEL>2) fprintferr("delta[%ld] = %Z\n",i,p1);
/* g = prod (X - delta[i])
* if g o h = 0 (pol), we'll have h(Ai[j]) = delta[i] for all j */
/* fk[k] belongs to block number whichdelta[k] */
for (j=1; j<=d; j++) whichdelta[Ai[j]] = i;
if (typ(p1) == t_POL) p1 = constant_term(p1);
d_1_term = addii(d_1_term, p1);
}
d_1_term = centermod(d_1_term, pe); /* Tr(g) */
if (absi_cmp(d_1_term, gel(M,3)) > 0) {
if (DEBUGLEVEL>1) fprintferr("d-1 test failed\n");
return NULL;
}
g = FqV_roots_to_pol(delta, T, pe, 0);
g = centermod(polsimplify(g), pe); /* assume g in Z[X] */
if (DEBUGLEVEL>2) fprintferr("pol. found = %Z\n",g);
if (!ok_coeffs(g,M)) {
if (DEBUGLEVEL>1) fprintferr("coeff too big for pol g(x)\n");
return NULL;
}
if (!FpX_is_squarefree(g, p)) {
if (DEBUGLEVEL>1) fprintferr("changing f(x): p divides disc(g)\n");
compute_data(B);
return subfield(A, B);
}
lf = lg(firstroot); listdelta = cgetg(lf, t_VEC);
for (i=1; i<lf; i++) listdelta[i] = delta[whichdelta[firstroot[i]]];
if (DEBUGLEVEL) fprintferr("candidate = %Z\n", g);
e = embedding(g, B->DATA, B->S, B->PD->den, listdelta);
if (!e) return NULL;
if (DEBUGLEVEL) fprintferr("embedding = %Z\n", e);
return _subfield(g, e);
}
/* assume x in Fq, return Tr_{Fq/Fp}(x) as a t_INT */
static GEN
trace(GEN x, GEN Trq, GEN p)
{
long i, l;
GEN s;
if (typ(x) == t_INT) return modii(mulii(x, gel(Trq,1)), p);
l = lg(x)-1; if (l == 1) return gen_0;
x++; s = mulii(gel(x,1), gel(Trq,1));
for (i=2; i<l; i++)
s = addii(s, mulii(gel(x,i), gel(Trq,i)));
return modii(s, p);
}
/* pol^2 mod (polcyclo(5),N) */
static GEN
sqrmod5(GEN pol, Red *R)
{
GEN c2,b,c,d,A,B,C,D;
long lv = lg(pol);
if (lv==2) return pol;
if (lv==3) return sqrconst(pol, R);
c = gel(pol,3); c2 = shifti(c,1);
d = gel(pol,2);
if (lv==4)
{
A = sqri(d);
B = mulii(c2, d);
C = sqri(c);
A = centermodii(A, R->N, R->N2);
B = centermodii(B, R->N, R->N2);
C = centermodii(C, R->N, R->N2); return mkpoln(3,A,B,C);
}
b = gel(pol,4);
if (lv==5)
{
A = mulii(b, subii(c2,b));
B = addii(sqri(c), mulii(b, subii(shifti(d,1),b)));
C = subii(mulii(c2,d), sqri(b));
D = mulii(subii(d,b), addii(d,b));
}
else
{ /* lv == 6 */
GEN a = gel(pol,5), a2 = shifti(a,1);
/* 2a(d - c) + b(2c - b) */
A = addii(mulii(a2, subii(d,c)), mulii(b, subii(c2,b)));
/* c(c - 2a) + b(2d - b) */
B = addii(mulii(c, subii(c,a2)), mulii(b, subii(shifti(d,1),b)));
/* (a-b)(a+b) + 2c(d - a) */
C = addii(mulii(subii(a,b),addii(a,b)), mulii(c2,subii(d,a)));
/* 2a(b - c) + (d-b)(d+b) */
D = addii(mulii(a2, subii(b,c)), mulii(subii(d,b), addii(d,b)));
}
A = centermodii(A, R->N, R->N2);
B = centermodii(B, R->N, R->N2);
C = centermodii(C, R->N, R->N2);
D = centermodii(D, R->N, R->N2); return mkpoln(4,A,B,C,D);
}
}
// Return value: Did the user break out of the loop?
// Not stack clean.
int palhelper(long digits, GEN a, GEN b, GEN code)
{
GEN p10 = powuu(10, (digits+1)>>1);
GEN aLeft = divii(a, p10);
GEN bLeft = divii(b, p10);
GEN cur;
// TODO: Handle case of digits odd (middle digit)
pari_sp btop = avma, lim = stack_lim(btop,1);
cur = addii(mulii(aLeft, p10), rev(aLeft, 10));
if (cmpii(cur, a) < 0) {
aLeft = addis(aLeft, 1);
cur = addii(mulii(aLeft, p10), rev(aLeft, 10));
}
push_lex(cur, code);
while (cmpii(aLeft, bLeft) < 0)
{
closure_evalvoid(code);
if (loop_break()) {
pop_lex(1);
return(1);
}
//cur = get_lex(-1); // Allow the user to modify the variable
aLeft = addis(aLeft, 1);
int
ratlift(GEN x, GEN m, GEN *a, GEN *b, GEN amax, GEN bmax)
{
GEN d,d1,v,v1,q,r;
pari_sp av = avma, av1, lim;
long lb,lr,lbb,lbr,s,s0;
ulong vmax;
ulong xu,xu1,xv,xv1; /* Lehmer stage recurrence matrix */
int lhmres; /* Lehmer stage return value */
if ((typ(x) | typ(m) | typ(amax) | typ(bmax)) != t_INT) pari_err(arither1);
if (signe(bmax) <= 0)
pari_err(talker, "ratlift: bmax must be > 0, found\n\tbmax=%Z\n", bmax);
if (signe(amax) < 0)
pari_err(talker, "ratilft: amax must be >= 0, found\n\tamax=%Z\n", amax);
/* check 2*amax*bmax < m */
if (cmpii(shifti(mulii(amax, bmax), 1), m) >= 0)
pari_err(talker, "ratlift: must have 2*amax*bmax < m, found\n\tamax=%Z\n\tbmax=%Z\n\tm=%Z\n", amax,bmax,m);
/* we _could_ silently replace x with modii(x,m) instead of the following,
* but let's leave this up to the caller
*/
avma = av; s = signe(x);
if (s < 0 || cmpii(x,m) >= 0)
pari_err(talker, "ratlift: must have 0 <= x < m, found\n\tx=%Z\n\tm=%Z\n", x,m);
/* special cases x=0 and/or amax=0 */
if (s == 0)
{
if (a != NULL) *a = gen_0;
if (b != NULL) *b = gen_1;
return 1;
}
else if (signe(amax)==0)
return 0;
/* assert: m > x > 0, amax > 0 */
/* check here whether a=x, b=1 is a solution */
if (cmpii(x,amax) <= 0)
{
if (a != NULL) *a = icopy(x);
if (b != NULL) *b = gen_1;
return 1;
}
/* There is no special case for single-word numbers since this is
* mainly meant to be used with large moduli.
*/
(void)new_chunk(lgefint(bmax) + lgefint(amax)); /* room for a,b */
d = m; d1 = x;
v = gen_0; v1 = gen_1;
/* assert d1 > amax, v1 <= bmax here */
lb = lgefint(bmax);
lbb = bfffo(*int_MSW(bmax));
s = 1;
av1 = avma; lim = stack_lim(av, 1);
/* general case: Euclidean division chain starting with m div x, and
* with bounds on the sequence of convergents' denoms v_j.
* Just to be different from what invmod and bezout are doing, we work
* here with the all-nonnegative matrices [u,u1;v,v1]=prod_j([0,1;1,q_j]).
* Loop invariants:
* (a) (sign)*[-v,v1]*x = [d,d1] (mod m) (componentwise)
* (sign initially +1, changes with each Euclidean step)
* so [a,b] will be obtained in the form [-+d,v] or [+-d1,v1];
* this congruence is a consequence of
* (b) [x,m]~ = [u,u1;v,v1]*[d1,d]~,
* where u,u1 is the usual numerator sequence starting with 1,0
* instead of 0,1 (just multiply the eqn on the left by the inverse
* matrix, which is det*[v1,-u1;-v,u], where "det" is the same as the
* "(sign)" in (a)). From m = v*d1 + v1*d and
* (c) d > d1 >= 0, 0 <= v < v1,
* we have d >= m/(2*v1), so while v1 remains smaller than m/(2*amax),
* the pair [-(sign)*d,v] satisfies (1) but violates (2) (d > amax).
* Conversely, v1 > bmax indicates that no further solutions will be
* forthcoming; [-(sign)*d,v] will be the last, and first, candidate.
* Thus there's at most one point in the chain division where a solution
* can live: v < bmax, v1 >= m/(2*amax) > bmax, and this is acceptable
* iff in fact d <= amax (e.g. m=221, x=34 or 35, amax=bmax=10 fail on
* this count while x=32,33,36,37 succeed). However, a division may leave
* a zero residue before we ever reach this point (consider m=210, x=35,
* amax=bmax=10), and our caller may find that gcd(d,v) > 1 (numerous
* examples -- keep m=210 and consider any of x=29,31,32,33,34,36,37,38,
* 39,40,41).
* Furthermore, at the start of the loop body we have in fact
* (c') 0 <= v < v1 <= bmax, d > d1 > amax >= 0,
* (and are never done already).
*
* Main loop is similar to those of invmod() and bezout(), except for
* having to determine appropriate vmax bounds, and checking termination
* conditions. The signe(d1) condition is only for paranoia
*/
while (lgefint(d) > 3 && signe(d1))
{
/* determine vmax for lgcdii so as to ensure v won't overshoot.
* If v+v1 > bmax, the next step would take v1 beyond the limit, so
* since [+-d1,v1] is not a solution, we give up. Otherwise if v+v1
* is way shorter than bmax, use vmax=MAXULUNG. Otherwise, set vmax
* to a crude lower approximation of bmax/(v+v1), or to 1, which will
* allow the inner loop to do one step
*/
r = addii(v,v1);
lr = lb - lgefint(r);
lbr = bfffo(*int_MSW(r));
if (cmpii(r,bmax) > 0) /* done, not found */
{
avma = av;
return 0;
}
else if (lr > 1) /* still more than a word's worth to go */
{
vmax = MAXULONG;
}
else /* take difference of bit lengths */
{
lr = (lr << TWOPOTBITS_IN_LONG) - lbb + lbr;
if ((ulong)lr > BITS_IN_LONG)
vmax = MAXULONG;
else if (lr == 0)
vmax = 1UL;
else
vmax = 1UL << (lr-1);
/* the latter is pessimistic but faster than a division */
}
/* do a Lehmer-Jebelean round */
lhmres = lgcdii((ulong *)d, (ulong *)d1, &xu, &xu1, &xv, &xv1, vmax);
if (lhmres != 0) /* check progress */
{ /* apply matrix */
if ((lhmres == 1) || (lhmres == -1))
{
s = -s;
if (xv1 == 1)
{
/* re-use v+v1 computed above */
v=v1; v1=r;
r = subii(d,d1); d=d1; d1=r;
}
else
{
r = subii(d, mului(xv1,d1)); d=d1; d1=r;
r = addii(v, mului(xv1,v1)); v=v1; v1=r;
}
}
else
{
r = subii(muliu(d,xu), muliu(d1,xv));
d1 = subii(muliu(d,xu1), muliu(d1,xv1)); d = r;
r = addii(muliu(v,xu), muliu(v1,xv));
v1 = addii(muliu(v,xu1), muliu(v1,xv1)); v = r;
if (lhmres&1)
{
setsigne(d,-signe(d));
s = -s;
}
else if (signe(d1))
{
setsigne(d1,-signe(d1));
}
}
/* check whether we're done. Assert v <= bmax here. Examine v1:
* if v1 > bmax, check d and return 0 or 1 depending on the outcome;
* if v1 <= bmax, check d1 and return 1 if d1 <= amax, otherwise
* proceed.
*/
if (cmpii(v1,bmax) > 0) /* certainly done */
{
avma = av;
if (cmpii(d,amax) <= 0) /* done, found */
{
if (a != NULL)
{
*a = icopy(d);
setsigne(*a,-s); /* sign opposite to s */
}
if (b != NULL) *b = icopy(v);
return 1;
}
else /* done, not found */
return 0;
}
else if (cmpii(d1,amax) <= 0) /* also done, found */
{
avma = av;
if (a != NULL)
{
if (signe(d1))
{
*a = icopy(d1);
setsigne(*a,s); /* same sign as s */
}
else
*a = gen_0;
}
if (b != NULL) *b = icopy(v1);
return 1;
}
} /* lhmres != 0 */
if (lhmres <= 0 && signe(d1))
{
q = dvmdii(d,d1,&r);
#ifdef DEBUG_LEHMER
fprintferr("Full division:\n");
printf(" q = "); output(q); sleep (1);
#endif
d=d1; d1=r;
r = addii(v,mulii(q,v1));
v=v1; v1=r;
s = -s;
/* check whether we are done now. Since we weren't before the div, it
* suffices to examine v1 and d1 -- the new d (former d1) cannot cut it
*/
if (cmpii(v1,bmax) > 0) /* done, not found */
{
avma = av;
return 0;
}
else if (cmpii(d1,amax) <= 0) /* done, found */
{
avma = av;
if (a != NULL)
{
if (signe(d1))
{
*a = icopy(d1);
setsigne(*a,s); /* same sign as s */
}
else
*a = gen_0;
}
if (b != NULL) *b = icopy(v1);
return 1;
}
}
if (low_stack(lim, stack_lim(av,1)))
{
GEN *gptr[4]; gptr[0]=&d; gptr[1]=&d1; gptr[2]=&v; gptr[3]=&v1;
if(DEBUGMEM>1) pari_warn(warnmem,"ratlift");
gerepilemany(av1,gptr,4);
}
} /* end while */
/* Postprocessing - final sprint. Since we usually underestimate vmax,
* this function needs a loop here instead of a simple conditional.
* Note we can only get here when amax fits into one word (which will
* typically not be the case!). The condition is bogus -- d1 is never
* zero at the start of the loop. There will be at most a few iterations,
* so we don't bother collecting garbage
*/
while (signe(d1))
{
/* Assertions: lgefint(d)==lgefint(d1)==3.
* Moreover, we aren't done already, or we would have returned by now.
* Recompute vmax...
*/
#ifdef DEBUG_RATLIFT
fprintferr("rl-fs: d,d1=%Z,%Z\n", d, d1);
fprintferr("rl-fs: v,v1=%Z,%Z\n", v, v1);
#endif
r = addii(v,v1);
lr = lb - lgefint(r);
lbr = bfffo(*int_MSW(r));
if (cmpii(r,bmax) > 0) /* done, not found */
{
avma = av;
return 0;
}
else if (lr > 1) /* still more than a word's worth to go */
{
vmax = MAXULONG; /* (cannot in fact happen) */
}
else /* take difference of bit lengths */
{
lr = (lr << TWOPOTBITS_IN_LONG) - lbb + lbr;
if ((ulong)lr > BITS_IN_LONG)
vmax = MAXULONG;
else if (lr == 0)
vmax = 1UL;
else
vmax = 1UL << (lr-1); /* as above */
}
#ifdef DEBUG_RATLIFT
fprintferr("rl-fs: vmax=%lu\n", vmax);
#endif
/* single-word "Lehmer", discarding the gcd or whatever it returns */
(void)rgcduu((ulong)*int_MSW(d), (ulong)*int_MSW(d1), vmax, &xu, &xu1, &xv, &xv1, &s0);
#ifdef DEBUG_RATLIFT
fprintferr("rl-fs: [%lu,%lu; %lu,%lu] %s\n",
xu, xu1, xv, xv1,
s0 < 0 ? "-" : "+");
#endif
if (xv1 == 1) /* avoid multiplications */
{
/* re-use v+v1 computed above */
v=v1; v1=r;
r = subii(d,d1); d=d1; d1=r;
s = -s;
}
else if (xu == 0) /* and xv==1, xu1==1, xv1 > 1 */
{
r = subii(d, mului(xv1,d1)); d=d1; d1=r;
r = addii(v, mului(xv1,v1)); v=v1; v1=r;
s = -s;
}
else
{
r = subii(muliu(d,xu), muliu(d1,xv));
d1 = subii(muliu(d,xu1), muliu(d1,xv1)); d = r;
r = addii(muliu(v,xu), muliu(v1,xv));
v1 = addii(muliu(v,xu1), muliu(v1,xv1)); v = r;
if (s0 < 0)
{
setsigne(d,-signe(d));
s = -s;
}
else if (signe(d1)) /* sic: might vanish now */
{
setsigne(d1,-signe(d1));
}
}
/* check whether we're done, as above. Assert v <= bmax. Examine v1:
* if v1 > bmax, check d and return 0 or 1 depending on the outcome;
* if v1 <= bmax, check d1 and return 1 if d1 <= amax, otherwise proceed.
*/
if (cmpii(v1,bmax) > 0) /* certainly done */
{
avma = av;
if (cmpii(d,amax) <= 0) /* done, found */
{
if (a != NULL)
{
*a = icopy(d);
setsigne(*a,-s); /* sign opposite to s */
}
if (b != NULL) *b = icopy(v);
return 1;
}
else /* done, not found */
return 0;
}
else if (cmpii(d1,amax) <= 0) /* also done, found */
{
avma = av;
if (a != NULL)
{
if (signe(d1))
{
*a = icopy(d1);
setsigne(*a,s); /* same sign as s */
}
else
*a = gen_0;
}
if (b != NULL) *b = icopy(v1);
return 1;
}
} /* while */
/* get here when we have run into d1 == 0 before returning... in fact,
* this cannot happen.
*/
pari_err(talker, "ratlift failed to catch d1 == 0\n");
/* NOTREACHED */
return 0;
}
