void
mpz_divexact (mpz_ptr quot, mpz_srcptr num, mpz_srcptr den)
{
mp_ptr qp;
mp_size_t qn;
mp_srcptr np, dp;
mp_size_t nn, dn;
TMP_DECL;
#if WANT_ASSERT
{
mpz_t rem;
mpz_init (rem);
mpz_tdiv_r (rem, num, den);
ASSERT (SIZ(rem) == 0);
mpz_clear (rem);
}
#endif
nn = ABSIZ (num);
dn = ABSIZ (den);
if (nn < dn)
{
/* This special case avoids segfaults below when the function is
incorrectly called with |N| < |D|, N != 0. It also handles the
well-defined case N = 0. */
SIZ(quot) = 0;
return;
}
qn = nn - dn + 1;
TMP_MARK;
if (quot == num || quot == den)
qp = TMP_ALLOC_LIMBS (qn);
else
qp = MPZ_REALLOC (quot, qn);
np = PTR(num);
dp = PTR(den);
mpn_divexact (qp, np, nn, dp, dn);
MPN_NORMALIZE (qp, qn);
if (qp != PTR(quot))
MPN_COPY (MPZ_REALLOC (quot, qn), qp, qn);
SIZ(quot) = (SIZ(num) ^ SIZ(den)) >= 0 ? qn : -qn;
TMP_FREE;
}
/* Computes |v| = |(g - u a)| / b, where u may be positive or
negative, and v is of the opposite sign. a, b are of size n, u and
v at most size n, and v must have space for n+1 limbs. */
static mp_size_t
compute_v (mp_ptr vp,
mp_srcptr ap, mp_srcptr bp, mp_size_t n,
mp_srcptr gp, mp_size_t gn,
mp_srcptr up, mp_size_t usize,
mp_ptr tp)
{
mp_size_t size;
mp_size_t an;
mp_size_t bn;
mp_size_t vn;
ASSERT (n > 0);
ASSERT (gn > 0);
ASSERT (usize != 0);
size = ABS (usize);
ASSERT (size <= n);
an = n;
MPN_NORMALIZE (ap, an);
if (an >= size)
mpn_mul (tp, ap, an, up, size);
else
mpn_mul (tp, up, size, ap, an);
size += an;
size -= tp[size - 1] == 0;
ASSERT (gn <= size);
if (usize > 0)
{
/* |v| = -v = (u a - g) / b */
ASSERT_NOCARRY (mpn_sub (tp, tp, size, gp, gn));
MPN_NORMALIZE (tp, size);
if (size == 0)
return 0;
}
else
{ /* usize < 0 */
/* |v| = v = (c - u a) / b = (c + |u| a) / b */
mp_limb_t cy = mpn_add (tp, tp, size, gp, gn);
if (cy)
tp[size++] = cy;
}
/* Now divide t / b. There must be no remainder */
bn = n;
MPN_NORMALIZE (bp, bn);
ASSERT (size >= bn);
vn = size + 1 - bn;
ASSERT (vn <= n + 1);
mpn_divexact (vp, tp, size, bp, bn);
vn -= (vp[vn-1] == 0);
return vn;
}