1 /* mpn_divrem_2 -- Divide natural numbers, producing both remainder and
2 quotient. The divisor is two limbs.
4 THIS FILE CONTAINS INTERNAL FUNCTIONS WITH MUTABLE INTERFACES. IT IS
5 ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS
6 ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP
10 Copyright (C) 1993, 1994, 1995, 1996, 1999, 2000 Free Software Foundation,
13 This file is part of the GNU MP Library.
15 The GNU MP Library is free software; you can redistribute it and/or modify
16 it under the terms of the GNU Lesser General Public License as published by
17 the Free Software Foundation; either version 2.1 of the License, or (at your
18 option) any later version.
20 The GNU MP Library is distributed in the hope that it will be useful, but
21 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
22 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
23 License for more details.
25 You should have received a copy of the GNU Lesser General Public License
26 along with the GNU MP Library; see the file COPYING.LIB. If not, write to
27 the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 MA 02111-1307, USA. */
34 /* Divide num (NP/NSIZE) by den (DP/2) and write
35 the NSIZE-2 least significant quotient limbs at QP
36 and the 2 long remainder at NP. If QEXTRA_LIMBS is
37 non-zero, generate that many fraction bits and append them after the
39 Return the most significant limb of the quotient, this is always 0 or 1.
43 1. The most significant bit of the divisor must be set.
44 2. QP must either not overlap with the input operands at all, or
45 QP + 2 >= NP must hold true. (This means that it's
46 possible to put the quotient in the high part of NUM, right after the
48 3. NSIZE >= 2, even if QEXTRA_LIMBS is non-zero. */
52 mpn_divrem_2 (mp_ptr qp, mp_size_t qxn,
53 mp_ptr np, mp_size_t nsize,
56 mpn_divrem_2 (qp, qxn, np, nsize, dp)
64 mp_limb_t most_significant_q_limb = 0;
77 if (n1 >= d1 && (n1 > d1 || n0 >= d0))
79 sub_ddmmss (n1, n0, n1, n0, d1, d0);
80 most_significant_q_limb = 1;
83 /* If multiplication is much faster than division, preinvert the most
84 significant divisor limb before entering the loop. */
85 if (UDIV_TIME > 2 * UMUL_TIME + 6)
88 if ((UDIV_TIME - (2 * UMUL_TIME + 6)) * (nsize - 2) > UDIV_TIME)
90 invert_limb (d1inv, d1);
95 for (i = qxn + nsize - 2 - 1; i >= 0; i--)
107 /* Q should be either 111..111 or 111..110. Need special treatment
108 of this rare case as normal division would give overflow. */
112 if (r < d1) /* Carry in the addition? */
114 add_ssaaaa (n1, n0, r - d0, np[0], 0, d0);
123 if (UDIV_TIME > 2 * UMUL_TIME + 6 && have_preinv)
124 udiv_qrnnd_preinv (q, r, n1, n0, d1, d1inv);
126 udiv_qrnnd (q, r, n1, n0, d1);
127 umul_ppmm (n1, n0, d0, q);
133 if (n1 > r || (n1 == r && n0 > n2))
135 /* The estimated Q was too large. */
138 sub_ddmmss (n1, n0, n1, n0, 0, d0);
140 if (r >= d1) /* If not carry, test Q again. */
145 sub_ddmmss (n1, n0, r, n2, n1, n0);
150 return most_significant_q_limb;