1 /* mpn_divrem_2 -- Divide natural numbers, producing both remainder and
2 quotient. The divisor is two limbs.
3
4 THIS FILE CONTAINS INTERNAL FUNCTIONS WITH MUTABLE INTERFACES. IT IS ONLY
5 SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
6 GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
7
8
9 Copyright 1993-1996, 1999-2002 Free Software Foundation, Inc.
10
11 This file is part of the GNU MP Library.
12
13 The GNU MP Library is free software; you can redistribute it and/or modify
14 it under the terms of either:
15
16 * the GNU Lesser General Public License as published by the Free
17 Software Foundation; either version 3 of the License, or (at your
18 option) any later version.
19
20 or
21
22 * the GNU General Public License as published by the Free Software
23 Foundation; either version 2 of the License, or (at your option) any
24 later version.
25
26 or both in parallel, as here.
27
28 The GNU MP Library is distributed in the hope that it will be useful, but
29 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
30 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
31 for more details.
32
33 You should have received copies of the GNU General Public License and the
34 GNU Lesser General Public License along with the GNU MP Library. If not,
35 see https://www.gnu.org/licenses/. */
36
37 #include "gmp-impl.h"
38 #include "longlong.h"
39
40
41 /* Divide num {np,nn} by den {dp,2} and write the nn-2 least significant
42 quotient limbs at qp and the 2 long remainder at np. If qxn is non-zero,
43 generate that many fraction bits and append them after the other quotient
44 limbs. Return the most significant limb of the quotient, this is always 0
45 or 1.
46
47 Preconditions:
48 1. The most significant bit of the divisor must be set.
49 2. qp must either not overlap with the input operands at all, or
50 qp >= np + 2 must hold true. (This means that it's possible to put
51 the quotient in the high part of {np,nn}, right above the remainder.
52 3. nn >= 2, even if qxn is non-zero. */
53
54 mp_limb_t
mpn_divrem_2(mp_ptr qp,mp_size_t qxn,mp_ptr np,mp_size_t nn,mp_srcptr dp)55 mpn_divrem_2 (mp_ptr qp, mp_size_t qxn,
56 mp_ptr np, mp_size_t nn,
57 mp_srcptr dp)
58 {
59 mp_limb_t most_significant_q_limb;
60 mp_size_t i;
61 mp_limb_t r1, r0, d1, d0;
62 gmp_pi1_t di;
63
64 ASSERT (nn >= 2);
65 ASSERT (qxn >= 0);
66 ASSERT (dp[1] & GMP_NUMB_HIGHBIT);
67 ASSERT (! MPN_OVERLAP_P (qp, nn-2+qxn, np, nn) || qp >= np+2);
68 ASSERT_MPN (np, nn);
69 ASSERT_MPN (dp, 2);
70
71 np += nn - 2;
72 d1 = dp[1];
73 d0 = dp[0];
74 r1 = np[1];
75 r0 = np[0];
76
77 most_significant_q_limb = 0;
78 if (r1 >= d1 && (r1 > d1 || r0 >= d0))
79 {
80 #if GMP_NAIL_BITS == 0
81 sub_ddmmss (r1, r0, r1, r0, d1, d0);
82 #else
83 r0 = r0 - d0;
84 r1 = r1 - d1 - (r0 >> GMP_LIMB_BITS - 1);
85 r0 &= GMP_NUMB_MASK;
86 #endif
87 most_significant_q_limb = 1;
88 }
89
90 invert_pi1 (di, d1, d0);
91
92 qp += qxn;
93
94 for (i = nn - 2 - 1; i >= 0; i--)
95 {
96 mp_limb_t n0, q;
97 n0 = np[-1];
98 udiv_qr_3by2 (q, r1, r0, r1, r0, n0, d1, d0, di.inv32);
99 np--;
100 qp[i] = q;
101 }
102
103 if (UNLIKELY (qxn != 0))
104 {
105 qp -= qxn;
106 for (i = qxn - 1; i >= 0; i--)
107 {
108 mp_limb_t q;
109 udiv_qr_3by2 (q, r1, r0, r1, r0, CNST_LIMB(0), d1, d0, di.inv32);
110 qp[i] = q;
111 }
112 }
113
114 np[1] = r1;
115 np[0] = r0;
116
117 return most_significant_q_limb;
118 }
119