--- /dev/null
+/* mpn_divrem_2 -- Divide natural numbers, producing both remainder and
+ quotient. The divisor is two limbs.
+
+ THIS FILE CONTAINS INTERNAL FUNCTIONS WITH MUTABLE INTERFACES. IT IS
+ ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS
+ ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP
+ RELEASE.
+
+
+Copyright (C) 1993, 1994, 1995, 1996, 1999, 2000 Free Software Foundation,
+Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library; see the file COPYING.LIB. If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+/* Divide num (NP/NSIZE) by den (DP/2) and write
+ the NSIZE-2 least significant quotient limbs at QP
+ and the 2 long remainder at NP. If QEXTRA_LIMBS is
+ non-zero, generate that many fraction bits and append them after the
+ other quotient limbs.
+ Return the most significant limb of the quotient, this is always 0 or 1.
+
+ Preconditions:
+ 0. NSIZE >= 2.
+ 1. The most significant bit of the divisor must be set.
+ 2. QP must either not overlap with the input operands at all, or
+ QP + 2 >= NP must hold true. (This means that it's
+ possible to put the quotient in the high part of NUM, right after the
+ remainder in NUM.
+ 3. NSIZE >= 2, even if QEXTRA_LIMBS is non-zero. */
+
+mp_limb_t
+#if __STDC__
+mpn_divrem_2 (mp_ptr qp, mp_size_t qxn,
+ mp_ptr np, mp_size_t nsize,
+ mp_srcptr dp)
+#else
+mpn_divrem_2 (qp, qxn, np, nsize, dp)
+ mp_ptr qp;
+ mp_size_t qxn;
+ mp_ptr np;
+ mp_size_t nsize;
+ mp_srcptr dp;
+#endif
+{
+ mp_limb_t most_significant_q_limb = 0;
+ mp_size_t i;
+ mp_limb_t n1, n0, n2;
+ mp_limb_t d1, d0;
+ mp_limb_t d1inv;
+ int have_preinv;
+
+ np += nsize - 2;
+ d1 = dp[1];
+ d0 = dp[0];
+ n1 = np[1];
+ n0 = np[0];
+
+ if (n1 >= d1 && (n1 > d1 || n0 >= d0))
+ {
+ sub_ddmmss (n1, n0, n1, n0, d1, d0);
+ most_significant_q_limb = 1;
+ }
+
+ /* If multiplication is much faster than division, preinvert the most
+ significant divisor limb before entering the loop. */
+ if (UDIV_TIME > 2 * UMUL_TIME + 6)
+ {
+ have_preinv = 0;
+ if ((UDIV_TIME - (2 * UMUL_TIME + 6)) * (nsize - 2) > UDIV_TIME)
+ {
+ invert_limb (d1inv, d1);
+ have_preinv = 1;
+ }
+ }
+
+ for (i = qxn + nsize - 2 - 1; i >= 0; i--)
+ {
+ mp_limb_t q;
+ mp_limb_t r;
+
+ if (i >= qxn)
+ np--;
+ else
+ np[0] = 0;
+
+ if (n1 == d1)
+ {
+ /* Q should be either 111..111 or 111..110. Need special treatment
+ of this rare case as normal division would give overflow. */
+ q = ~(mp_limb_t) 0;
+
+ r = n0 + d1;
+ if (r < d1) /* Carry in the addition? */
+ {
+ add_ssaaaa (n1, n0, r - d0, np[0], 0, d0);
+ qp[i] = q;
+ continue;
+ }
+ n1 = d0 - (d0 != 0);
+ n0 = -d0;
+ }
+ else
+ {
+ if (UDIV_TIME > 2 * UMUL_TIME + 6 && have_preinv)
+ udiv_qrnnd_preinv (q, r, n1, n0, d1, d1inv);
+ else
+ udiv_qrnnd (q, r, n1, n0, d1);
+ umul_ppmm (n1, n0, d0, q);
+ }
+
+ n2 = np[0];
+
+ q_test:
+ if (n1 > r || (n1 == r && n0 > n2))
+ {
+ /* The estimated Q was too large. */
+ q--;
+
+ sub_ddmmss (n1, n0, n1, n0, 0, d0);
+ r += d1;
+ if (r >= d1) /* If not carry, test Q again. */
+ goto q_test;
+ }
+
+ qp[i] = q;
+ sub_ddmmss (n1, n0, r, n2, n1, n0);
+ }
+ np[1] = n1;
+ np[0] = n0;
+
+ return most_significant_q_limb;
+}
projects / ghc-hetmet.git / blobdiff